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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Routines having to do with the 'struct sk_buff' memory handlers.
  *
  *  Authors:    Alan Cox <alan@lxorguk.ukuu.org.uk>
  *          Florian La Roche <rzsfl@rz.uni-sb.de>
  *
  *  Fixes:
  *      Alan Cox    :   Fixed the worst of the load
  *                  balancer bugs.
  *      Dave Platt  :   Interrupt stacking fix.
  *  Richard Kooijman    :   Timestamp fixes.
  *      Alan Cox    :   Changed buffer format.
  *      Alan Cox    :   destructor hook for AF_UNIX etc.
  *      Linus Torvalds  :   Better skb_clone.
  *      Alan Cox    :   Added skb_copy.
  *      Alan Cox    :   Added all the changed routines Linus
  *                  only put in the headers
  *      Ray VanTassle   :   Fixed --skb->lock in free
  *      Alan Cox    :   skb_copy copy arp field
  *      Andi Kleen  :   slabified it.
  *      Robert Olsson   :   Removed skb_head_pool
  *
  *  NOTE:
  *      The __skb_ routines should be called with interrupts
  *  disabled, or you better be *real* sure that the operation is atomic
  *  with respect to whatever list is being frobbed (e.g. via lock_sock()
  *  or via disabling bottom half handlers, etc).
  */
 
 /*
  *  The functions in this file will not compile correctly with gcc 2.4.x
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/interrupt.h>
 #include <linux/in.h>
 #include <linux/inet.h>
 #include <linux/slab.h>
 #include <linux/tcp.h>
 #include <linux/udp.h>
 #include <linux/sctp.h>
 #include <linux/netdevice.h>
 #ifdef CONFIG_NET_CLS_ACT
 #include <net/pkt_sched.h>
 #endif
 #include <linux/string.h>
 #include <linux/skbuff.h>
 #include <linux/splice.h>
 #include <linux/cache.h>
 #include <linux/rtnetlink.h>
 #include <linux/init.h>
 #include <linux/scatterlist.h>
 #include <linux/errqueue.h>
 #include <linux/prefetch.h>
 #include <linux/if_vlan.h>
 #include <linux/mpls.h>
 #include <linux/kcov.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
 #include <net/sock.h>
 #include <net/checksum.h>
 #include <net/ip6_checksum.h>
 #include <net/xfrm.h>
 #include <net/mpls.h>
 #include <net/mptcp.h>
 #include <net/mctp.h>
 #include <net/page_pool.h>
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
 #include <linux/highmem.h>
 #include <linux/capability.h>
 #include <linux/user_namespace.h>
 #include <linux/indirect_call_wrapper.h>
 
 #include "dev.h"
 #include "sock_destructor.h"
 
 struct kmem_cache *skbuff_head_cache __ro_after_init;
 static struct kmem_cache *skbuff_fclone_cache __ro_after_init;
 #ifdef CONFIG_SKB_EXTENSIONS
 static struct kmem_cache *skbuff_ext_cache __ro_after_init;
 #endif
 int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
 EXPORT_SYMBOL(sysctl_max_skb_frags);
 
 #undef FN
 #define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
 const char * const drop_reasons[] = {
     DEFINE_DROP_REASON(FN, FN)
 };
 EXPORT_SYMBOL(drop_reasons);
 
 /**
  *  skb_panic - private function for out-of-line support
  *  @skb:   buffer
  *  @sz:    size
  *  @addr:  address
  *  @msg:   skb_over_panic or skb_under_panic
  *
  *  Out-of-line support for skb_put() and skb_push().
  *  Called via the wrapper skb_over_panic() or skb_under_panic().
  *  Keep out of line to prevent kernel bloat.
  *  __builtin_return_address is not used because it is not always reliable.
  */
 static void skb_panic(struct sk_buff *skb, unsigned int sz, void *addr,
               const char msg[])
 {
     pr_emerg("%s: text:%px len:%d put:%d head:%px data:%px tail:%#lx end:%#lx dev:%s\n",
          msg, addr, skb->len, sz, skb->head, skb->data,
          (unsigned long)skb->tail, (unsigned long)skb->end,
          skb->dev ? skb->dev->name : "<NULL>");
     BUG();
 }
 
 static void skb_over_panic(struct sk_buff *skb, unsigned int sz, void *addr)
 {
     skb_panic(skb, sz, addr, __func__);
 }
 
 static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
 {
     skb_panic(skb, sz, addr, __func__);
 }
 
 #define NAPI_SKB_CACHE_SIZE 64
 #define NAPI_SKB_CACHE_BULK 16
 #define NAPI_SKB_CACHE_HALF (NAPI_SKB_CACHE_SIZE / 2)
 
 struct napi_alloc_cache {
     struct page_frag_cache page;
     unsigned int skb_count;
     void *skb_cache[NAPI_SKB_CACHE_SIZE];
 };
 
 static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
 static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache);
 
 void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
 {
     struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
 
     fragsz = SKB_DATA_ALIGN(fragsz);
 
     return page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC, align_mask);
 }
 EXPORT_SYMBOL(__napi_alloc_frag_align);
 
 void *__netdev_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
 {
     void *data;
 
     fragsz = SKB_DATA_ALIGN(fragsz);
     if (in_hardirq() || irqs_disabled()) {
         struct page_frag_cache *nc = this_cpu_ptr(&netdev_alloc_cache);
 
         data = page_frag_alloc_align(nc, fragsz, GFP_ATOMIC, align_mask);
     } else {
         struct napi_alloc_cache *nc;
 
         local_bh_disable();
         nc = this_cpu_ptr(&napi_alloc_cache);
         data = page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC, align_mask);
         local_bh_enable();
     }
     return data;
 }
 EXPORT_SYMBOL(__netdev_alloc_frag_align);
 
 static struct sk_buff *napi_skb_cache_get(void)
 {
     struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
     struct sk_buff *skb;
 
     if (unlikely(!nc->skb_count)) {
         nc->skb_count = kmem_cache_alloc_bulk(skbuff_head_cache,
                               GFP_ATOMIC,
                               NAPI_SKB_CACHE_BULK,
                               nc->skb_cache);
         if (unlikely(!nc->skb_count))
             return NULL;
     }
 
     skb = nc->skb_cache[--nc->skb_count];
     kasan_unpoison_object_data(skbuff_head_cache, skb);
 
     return skb;
 }
 
 /* Caller must provide SKB that is memset cleared */
 static void __build_skb_around(struct sk_buff *skb, void *data,
                    unsigned int frag_size)
 {
     struct skb_shared_info *shinfo;
     unsigned int size = frag_size ? : ksize(data);
 
     size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
     /* Assumes caller memset cleared SKB */
     skb->truesize = SKB_TRUESIZE(size);
     refcount_set(&skb->users, 1);
     skb->head = data;
     skb->data = data;
     skb_reset_tail_pointer(skb);
     skb_set_end_offset(skb, size);
     skb->mac_header = (typeof(skb->mac_header))~0U;
     skb->transport_header = (typeof(skb->transport_header))~0U;
     skb->alloc_cpu = raw_smp_processor_id();
     /* make sure we initialize shinfo sequentially */
     shinfo = skb_shinfo(skb);
     memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
     atomic_set(&shinfo->dataref, 1);
 
     skb_set_kcov_handle(skb, kcov_common_handle());
 }
 
 /**
  * __build_skb - build a network buffer
  * @data: data buffer provided by caller
  * @frag_size: size of data, or 0 if head was kmalloced
  *
  * Allocate a new &sk_buff. Caller provides space holding head and
  * skb_shared_info. @data must have been allocated by kmalloc() only if
  * @frag_size is 0, otherwise data should come from the page allocator
  *  or vmalloc()
  * The return is the new skb buffer.
  * On a failure the return is %NULL, and @data is not freed.
  * Notes :
  *  Before IO, driver allocates only data buffer where NIC put incoming frame
  *  Driver should add room at head (NET_SKB_PAD) and
  *  MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info))
  *  After IO, driver calls build_skb(), to allocate sk_buff and populate it
  *  before giving packet to stack.
  *  RX rings only contains data buffers, not full skbs.
  */
 struct sk_buff *__build_skb(void *data, unsigned int frag_size)
 {
     struct sk_buff *skb;
 
     skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
     if (unlikely(!skb))
         return NULL;
 
     memset(skb, 0, offsetof(struct sk_buff, tail));
     __build_skb_around(skb, data, frag_size);
 
     return skb;
 }
 
 /* build_skb() is wrapper over __build_skb(), that specifically
  * takes care of skb->head and skb->pfmemalloc
  * This means that if @frag_size is not zero, then @data must be backed
  * by a page fragment, not kmalloc() or vmalloc()
  */
 struct sk_buff *build_skb(void *data, unsigned int frag_size)
 {
     struct sk_buff *skb = __build_skb(data, frag_size);
 
     if (skb && frag_size) {
         skb->head_frag = 1;
         if (page_is_pfmemalloc(virt_to_head_page(data)))
             skb->pfmemalloc = 1;
     }
     return skb;
 }
 EXPORT_SYMBOL(build_skb);
 
 /**
  * build_skb_around - build a network buffer around provided skb
  * @skb: sk_buff provide by caller, must be memset cleared
  * @data: data buffer provided by caller
  * @frag_size: size of data, or 0 if head was kmalloced
  */
 struct sk_buff *build_skb_around(struct sk_buff *skb,
                  void *data, unsigned int frag_size)
 {
     if (unlikely(!skb))
         return NULL;
 
     __build_skb_around(skb, data, frag_size);
 
     if (frag_size) {
         skb->head_frag = 1;
         if (page_is_pfmemalloc(virt_to_head_page(data)))
             skb->pfmemalloc = 1;
     }
     return skb;
 }
 EXPORT_SYMBOL(build_skb_around);
 
 /**
  * __napi_build_skb - build a network buffer
  * @data: data buffer provided by caller
  * @frag_size: size of data, or 0 if head was kmalloced
  *
  * Version of __build_skb() that uses NAPI percpu caches to obtain
  * skbuff_head instead of inplace allocation.
  *
  * Returns a new &sk_buff on success, %NULL on allocation failure.
  */
 static struct sk_buff *__napi_build_skb(void *data, unsigned int frag_size)
 {
     struct sk_buff *skb;
 
     skb = napi_skb_cache_get();
     if (unlikely(!skb))
         return NULL;
 
     memset(skb, 0, offsetof(struct sk_buff, tail));
     __build_skb_around(skb, data, frag_size);
 
     return skb;
 }
 
 /**
  * napi_build_skb - build a network buffer
  * @data: data buffer provided by caller
  * @frag_size: size of data, or 0 if head was kmalloced
  *
  * Version of __napi_build_skb() that takes care of skb->head_frag
  * and skb->pfmemalloc when the data is a page or page fragment.
  *
  * Returns a new &sk_buff on success, %NULL on allocation failure.
  */
 struct sk_buff *napi_build_skb(void *data, unsigned int frag_size)
 {
     struct sk_buff *skb = __napi_build_skb(data, frag_size);
 
     if (likely(skb) && frag_size) {
         skb->head_frag = 1;
         skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
     }
 
     return skb;
 }
 EXPORT_SYMBOL(napi_build_skb);
 
 /*
  * kmalloc_reserve is a wrapper around kmalloc_node_track_caller that tells
  * the caller if emergency pfmemalloc reserves are being used. If it is and
  * the socket is later found to be SOCK_MEMALLOC then PFMEMALLOC reserves
  * may be used. Otherwise, the packet data may be discarded until enough
  * memory is free
  */
 static void *kmalloc_reserve(size_t size, gfp_t flags, int node,
                  bool *pfmemalloc)
 {
     void *obj;
     bool ret_pfmemalloc = false;
 
     /*
      * Try a regular allocation, when that fails and we're not entitled
      * to the reserves, fail.
      */
     obj = kmalloc_node_track_caller(size,
                     flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
                     node);
     if (obj || !(gfp_pfmemalloc_allowed(flags)))
         goto out;
 
     /* Try again but now we are using pfmemalloc reserves */
     ret_pfmemalloc = true;
     obj = kmalloc_node_track_caller(size, flags, node);
 
 out:
     if (pfmemalloc)
         *pfmemalloc = ret_pfmemalloc;
 
     return obj;
 }
 
 /*  Allocate a new skbuff. We do this ourselves so we can fill in a few
  *  'private' fields and also do memory statistics to find all the
  *  [BEEP] leaks.
  *
  */
 
 /**
  *  __alloc_skb -   allocate a network buffer
  *  @size: size to allocate
  *  @gfp_mask: allocation mask
  *  @flags: If SKB_ALLOC_FCLONE is set, allocate from fclone cache
  *      instead of head cache and allocate a cloned (child) skb.
  *      If SKB_ALLOC_RX is set, __GFP_MEMALLOC will be used for
  *      allocations in case the data is required for writeback
  *  @node: numa node to allocate memory on
  *
  *  Allocate a new &sk_buff. The returned buffer has no headroom and a
  *  tail room of at least size bytes. The object has a reference count
  *  of one. The return is the buffer. On a failure the return is %NULL.
  *
  *  Buffers may only be allocated from interrupts using a @gfp_mask of
  *  %GFP_ATOMIC.
  */
 struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
                 int flags, int node)
 {
     struct kmem_cache *cache;
     struct sk_buff *skb;
     unsigned int osize;
     bool pfmemalloc;
     u8 *data;
 
     cache = (flags & SKB_ALLOC_FCLONE)
         ? skbuff_fclone_cache : skbuff_head_cache;
 
     if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
         gfp_mask |= __GFP_MEMALLOC;
 
     /* Get the HEAD */
     if ((flags & (SKB_ALLOC_FCLONE | SKB_ALLOC_NAPI)) == SKB_ALLOC_NAPI &&
         likely(node == NUMA_NO_NODE || node == numa_mem_id()))
         skb = napi_skb_cache_get();
     else
         skb = kmem_cache_alloc_node(cache, gfp_mask & ~GFP_DMA, node);
     if (unlikely(!skb))
         return NULL;
     prefetchw(skb);
 
     /* We do our best to align skb_shared_info on a separate cache
      * line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
      * aligned memory blocks, unless SLUB/SLAB debug is enabled.
      * Both skb->head and skb_shared_info are cache line aligned.
      */
     size = SKB_DATA_ALIGN(size);
     size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
     data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
     if (unlikely(!data))
         goto nodata;
     /* kmalloc(size) might give us more room than requested.
      * Put skb_shared_info exactly at the end of allocated zone,
      * to allow max possible filling before reallocation.
      */
     osize = ksize(data);
     size = SKB_WITH_OVERHEAD(osize);
     prefetchw(data + size);
 
     /*
      * Only clear those fields we need to clear, not those that we will
      * actually initialise below. Hence, don't put any more fields after
      * the tail pointer in struct sk_buff!
      */
     memset(skb, 0, offsetof(struct sk_buff, tail));
     __build_skb_around(skb, data, osize);
     skb->pfmemalloc = pfmemalloc;
 
     if (flags & SKB_ALLOC_FCLONE) {
         struct sk_buff_fclones *fclones;
 
         fclones = container_of(skb, struct sk_buff_fclones, skb1);
 
         skb->fclone = SKB_FCLONE_ORIG;
         refcount_set(&fclones->fclone_ref, 1);
     }
 
     return skb;
 
 nodata:
     kmem_cache_free(cache, skb);
     return NULL;
 }
 EXPORT_SYMBOL(__alloc_skb);
 
 /**
  *  __netdev_alloc_skb - allocate an skbuff for rx on a specific device
  *  @dev: network device to receive on
  *  @len: length to allocate
  *  @gfp_mask: get_free_pages mask, passed to alloc_skb
  *
  *  Allocate a new &sk_buff and assign it a usage count of one. The
  *  buffer has NET_SKB_PAD headroom built in. Users should allocate
  *  the headroom they think they need without accounting for the
  *  built in space. The built in space is used for optimisations.
  *
  *  %NULL is returned if there is no free memory.
  */
 struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
                    gfp_t gfp_mask)
 {
     struct page_frag_cache *nc;
     struct sk_buff *skb;
     bool pfmemalloc;
     void *data;
 
     len += NET_SKB_PAD;
 
     /* If requested length is either too small or too big,
      * we use kmalloc() for skb->head allocation.
      */
     if (len <= SKB_WITH_OVERHEAD(1024) ||
         len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
         (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
         skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
         if (!skb)
             goto skb_fail;
         goto skb_success;
     }
 
     len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
     len = SKB_DATA_ALIGN(len);
 
     if (sk_memalloc_socks())
         gfp_mask |= __GFP_MEMALLOC;
 
     if (in_hardirq() || irqs_disabled()) {
         nc = this_cpu_ptr(&netdev_alloc_cache);
         data = page_frag_alloc(nc, len, gfp_mask);
         pfmemalloc = nc->pfmemalloc;
     } else {
         local_bh_disable();
         nc = this_cpu_ptr(&napi_alloc_cache.page);
         data = page_frag_alloc(nc, len, gfp_mask);
         pfmemalloc = nc->pfmemalloc;
         local_bh_enable();
     }
 
     if (unlikely(!data))
         return NULL;
 
     skb = __build_skb(data, len);
     if (unlikely(!skb)) {
         skb_free_frag(data);
         return NULL;
     }
 
     if (pfmemalloc)
         skb->pfmemalloc = 1;
     skb->head_frag = 1;
 
 skb_success:
     skb_reserve(skb, NET_SKB_PAD);
     skb->dev = dev;
 
 skb_fail:
     return skb;
 }
 EXPORT_SYMBOL(__netdev_alloc_skb);
 
 /**
  *  __napi_alloc_skb - allocate skbuff for rx in a specific NAPI instance
  *  @napi: napi instance this buffer was allocated for
  *  @len: length to allocate
  *  @gfp_mask: get_free_pages mask, passed to alloc_skb and alloc_pages
  *
  *  Allocate a new sk_buff for use in NAPI receive.  This buffer will
  *  attempt to allocate the head from a special reserved region used
  *  only for NAPI Rx allocation.  By doing this we can save several
  *  CPU cycles by avoiding having to disable and re-enable IRQs.
  *
  *  %NULL is returned if there is no free memory.
  */
 struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
                  gfp_t gfp_mask)
 {
     struct napi_alloc_cache *nc;
     struct sk_buff *skb;
     void *data;
 
     DEBUG_NET_WARN_ON_ONCE(!in_softirq());
     len += NET_SKB_PAD + NET_IP_ALIGN;
 
     /* If requested length is either too small or too big,
      * we use kmalloc() for skb->head allocation.
      */
     if (len <= SKB_WITH_OVERHEAD(1024) ||
         len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
         (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
         skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX | SKB_ALLOC_NAPI,
                   NUMA_NO_NODE);
         if (!skb)
             goto skb_fail;
         goto skb_success;
     }
 
     nc = this_cpu_ptr(&napi_alloc_cache);
     len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
     len = SKB_DATA_ALIGN(len);
 
     if (sk_memalloc_socks())
         gfp_mask |= __GFP_MEMALLOC;
 
     data = page_frag_alloc(&nc->page, len, gfp_mask);
     if (unlikely(!data))
         return NULL;
 
     skb = __napi_build_skb(data, len);
     if (unlikely(!skb)) {
         skb_free_frag(data);
         return NULL;
     }
 
     if (nc->page.pfmemalloc)
         skb->pfmemalloc = 1;
     skb->head_frag = 1;
 
 skb_success:
     skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
     skb->dev = napi->dev;
 
 skb_fail:
     return skb;
 }
 EXPORT_SYMBOL(__napi_alloc_skb);
 
 void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
              int size, unsigned int truesize)
 {
     skb_fill_page_desc(skb, i, page, off, size);
     skb->len += size;
     skb->data_len += size;
     skb->truesize += truesize;
 }
 EXPORT_SYMBOL(skb_add_rx_frag);
 
 void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
               unsigned int truesize)
 {
     skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
     skb_frag_size_add(frag, size);
     skb->len += size;
     skb->data_len += size;
     skb->truesize += truesize;
 }
 EXPORT_SYMBOL(skb_coalesce_rx_frag);
 
 static void skb_drop_list(struct sk_buff **listp)
 {
     kfree_skb_list(*listp);
     *listp = NULL;
 }
 
 static inline void skb_drop_fraglist(struct sk_buff *skb)
 {
     skb_drop_list(&skb_shinfo(skb)->frag_list);
 }
 
 static void skb_clone_fraglist(struct sk_buff *skb)
 {
     struct sk_buff *list;
 
     skb_walk_frags(skb, list)
         skb_get(list);
 }
 
 static void skb_free_head(struct sk_buff *skb)
 {
     unsigned char *head = skb->head;
 
     if (skb->head_frag) {
         if (skb_pp_recycle(skb, head))
             return;
         skb_free_frag(head);
     } else {
         kfree(head);
     }
 }
 
 static void skb_release_data(struct sk_buff *skb)
 {
     struct skb_shared_info *shinfo = skb_shinfo(skb);
     int i;
 
     if (skb->cloned &&
         atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
                   &shinfo->dataref))
         goto exit;
 
     if (skb_zcopy(skb)) {
         bool skip_unref = shinfo->flags & SKBFL_MANAGED_FRAG_REFS;
 
         skb_zcopy_clear(skb, true);
         if (skip_unref)
             goto free_head;
     }
 
     for (i = 0; i < shinfo->nr_frags; i++)
         __skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
 
 free_head:
     if (shinfo->frag_list)
         kfree_skb_list(shinfo->frag_list);
 
     skb_free_head(skb);
 exit:
     /* When we clone an SKB we copy the reycling bit. The pp_recycle
      * bit is only set on the head though, so in order to avoid races
      * while trying to recycle fragments on __skb_frag_unref() we need
      * to make one SKB responsible for triggering the recycle path.
      * So disable the recycling bit if an SKB is cloned and we have
      * additional references to the fragmented part of the SKB.
      * Eventually the last SKB will have the recycling bit set and it's
      * dataref set to 0, which will trigger the recycling
      */
     skb->pp_recycle = 0;
 }
 
 /*
  *  Free an skbuff by memory without cleaning the state.
  */
 static void kfree_skbmem(struct sk_buff *skb)
 {
     struct sk_buff_fclones *fclones;
 
     switch (skb->fclone) {
     case SKB_FCLONE_UNAVAILABLE:
         kmem_cache_free(skbuff_head_cache, skb);
         return;
 
     case SKB_FCLONE_ORIG:
         fclones = container_of(skb, struct sk_buff_fclones, skb1);
 
         /* We usually free the clone (TX completion) before original skb
          * This test would have no chance to be true for the clone,
          * while here, branch prediction will be good.
          */
         if (refcount_read(&fclones->fclone_ref) == 1)
             goto fastpath;
         break;
 
     default: /* SKB_FCLONE_CLONE */
         fclones = container_of(skb, struct sk_buff_fclones, skb2);
         break;
     }
     if (!refcount_dec_and_test(&fclones->fclone_ref))
         return;
 fastpath:
     kmem_cache_free(skbuff_fclone_cache, fclones);
 }
 
 void skb_release_head_state(struct sk_buff *skb)
 {
     skb_dst_drop(skb);
     if (skb->destructor) {
         DEBUG_NET_WARN_ON_ONCE(in_hardirq());
         skb->destructor(skb);
     }
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
     nf_conntrack_put(skb_nfct(skb));
 #endif
     skb_ext_put(skb);
 }
 
 /* Free everything but the sk_buff shell. */
 static void skb_release_all(struct sk_buff *skb)
 {
     skb_release_head_state(skb);
     if (likely(skb->head))
         skb_release_data(skb);
 }
 
 /**
  *  __kfree_skb - private function
  *  @skb: buffer
  *
  *  Free an sk_buff. Release anything attached to the buffer.
  *  Clean the state. This is an internal helper function. Users should
  *  always call kfree_skb
  */
 
 void __kfree_skb(struct sk_buff *skb)
 {
     skb_release_all(skb);
     kfree_skbmem(skb);
 }
 EXPORT_SYMBOL(__kfree_skb);
 
 /**
  *  kfree_skb_reason - free an sk_buff with special reason
  *  @skb: buffer to free
  *  @reason: reason why this skb is dropped
  *
  *  Drop a reference to the buffer and free it if the usage count has
  *  hit zero. Meanwhile, pass the drop reason to 'kfree_skb'
  *  tracepoint.
  */
 void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 {
     if (!skb_unref(skb))
         return;
 
     DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
 
     trace_kfree_skb(skb, __builtin_return_address(0), reason);
     __kfree_skb(skb);
 }
 EXPORT_SYMBOL(kfree_skb_reason);
 
 void kfree_skb_list_reason(struct sk_buff *segs,
                enum skb_drop_reason reason)
 {
     while (segs) {
         struct sk_buff *next = segs->next;
 
         kfree_skb_reason(segs, reason);
         segs = next;
     }
 }
 EXPORT_SYMBOL(kfree_skb_list_reason);
 
 /* Dump skb information and contents.
  *
  * Must only be called from net_ratelimit()-ed paths.
  *
  * Dumps whole packets if full_pkt, only headers otherwise.
  */
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt)
 {
     struct skb_shared_info *sh = skb_shinfo(skb);
     struct net_device *dev = skb->dev;
     struct sock *sk = skb->sk;
     struct sk_buff *list_skb;
     bool has_mac, has_trans;
     int headroom, tailroom;
     int i, len, seg_len;
 
     if (full_pkt)
         len = skb->len;
     else
         len = min_t(int, skb->len, MAX_HEADER + 128);
 
     headroom = skb_headroom(skb);
     tailroom = skb_tailroom(skb);
 
     has_mac = skb_mac_header_was_set(skb);
     has_trans = skb_transport_header_was_set(skb);
 
     printk("%sskb len=%u headroom=%u headlen=%u tailroom=%u\n"
            "mac=(%d,%d) net=(%d,%d) trans=%d\n"
            "shinfo(txflags=%u nr_frags=%u gso(size=%hu type=%u segs=%hu))\n"
            "csum(0x%x ip_summed=%u complete_sw=%u valid=%u level=%u)\n"
            "hash(0x%x sw=%u l4=%u) proto=0x%04x pkttype=%u iif=%d\n",
            level, skb->len, headroom, skb_headlen(skb), tailroom,
            has_mac ? skb->mac_header : -1,
            has_mac ? skb_mac_header_len(skb) : -1,
            skb->network_header,
            has_trans ? skb_network_header_len(skb) : -1,
            has_trans ? skb->transport_header : -1,
            sh->tx_flags, sh->nr_frags,
            sh->gso_size, sh->gso_type, sh->gso_segs,
            skb->csum, skb->ip_summed, skb->csum_complete_sw,
            skb->csum_valid, skb->csum_level,
            skb->hash, skb->sw_hash, skb->l4_hash,
            ntohs(skb->protocol), skb->pkt_type, skb->skb_iif);
 
     if (dev)
         printk("%sdev name=%s feat=%pNF\n",
                level, dev->name, &dev->features);
     if (sk)
         printk("%ssk family=%hu type=%u proto=%u\n",
                level, sk->sk_family, sk->sk_type, sk->sk_protocol);
 
     if (full_pkt && headroom)
         print_hex_dump(level, "skb headroom: ", DUMP_PREFIX_OFFSET,
                    16, 1, skb->head, headroom, false);
 
     seg_len = min_t(int, skb_headlen(skb), len);
     if (seg_len)
         print_hex_dump(level, "skb linear:   ", DUMP_PREFIX_OFFSET,
                    16, 1, skb->data, seg_len, false);
     len -= seg_len;
 
     if (full_pkt && tailroom)
         print_hex_dump(level, "skb tailroom: ", DUMP_PREFIX_OFFSET,
                    16, 1, skb_tail_pointer(skb), tailroom, false);
 
     for (i = 0; len && i < skb_shinfo(skb)->nr_frags; i++) {
         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
         u32 p_off, p_len, copied;
         struct page *p;
         u8 *vaddr;
 
         skb_frag_foreach_page(frag, skb_frag_off(frag),
                       skb_frag_size(frag), p, p_off, p_len,
                       copied) {
             seg_len = min_t(int, p_len, len);
             vaddr = kmap_atomic(p);
             print_hex_dump(level, "skb frag:     ",
                        DUMP_PREFIX_OFFSET,
                        16, 1, vaddr + p_off, seg_len, false);
             kunmap_atomic(vaddr);
             len -= seg_len;
             if (!len)
                 break;
         }
     }
 
     if (full_pkt && skb_has_frag_list(skb)) {
         printk("skb fraglist:\n");
         skb_walk_frags(skb, list_skb)
             skb_dump(level, list_skb, true);
     }
 }
 EXPORT_SYMBOL(skb_dump);
 
 /**
  *  skb_tx_error - report an sk_buff xmit error
  *  @skb: buffer that triggered an error
  *
  *  Report xmit error if a device callback is tracking this skb.
  *  skb must be freed afterwards.
  */
 void skb_tx_error(struct sk_buff *skb)
 {
     if (skb) {
         skb_zcopy_downgrade_managed(skb);
         skb_zcopy_clear(skb, true);
     }
 }
 EXPORT_SYMBOL(skb_tx_error);
 
 #ifdef CONFIG_TRACEPOINTS
 /**
  *  consume_skb - free an skbuff
  *  @skb: buffer to free
  *
  *  Drop a ref to the buffer and free it if the usage count has hit zero
  *  Functions identically to kfree_skb, but kfree_skb assumes that the frame
  *  is being dropped after a failure and notes that
  */
 void consume_skb(struct sk_buff *skb)
 {
     if (!skb_unref(skb))
         return;
 
     trace_consume_skb(skb);
     __kfree_skb(skb);
 }
 EXPORT_SYMBOL(consume_skb);
 #endif
 
 /**
  *  __consume_stateless_skb - free an skbuff, assuming it is stateless
  *  @skb: buffer to free
  *
  *  Alike consume_skb(), but this variant assumes that this is the last
  *  skb reference and all the head states have been already dropped
  */
 void __consume_stateless_skb(struct sk_buff *skb)
 {
     trace_consume_skb(skb);
     skb_release_data(skb);
     kfree_skbmem(skb);
 }
 
 static void napi_skb_cache_put(struct sk_buff *skb)
 {
     struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
     u32 i;
 
     kasan_poison_object_data(skbuff_head_cache, skb);
     nc->skb_cache[nc->skb_count++] = skb;
 
     if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
         for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
             kasan_unpoison_object_data(skbuff_head_cache,
                            nc->skb_cache[i]);
 
         kmem_cache_free_bulk(skbuff_head_cache, NAPI_SKB_CACHE_HALF,
                      nc->skb_cache + NAPI_SKB_CACHE_HALF);
         nc->skb_count = NAPI_SKB_CACHE_HALF;
     }
 }
 
 void __kfree_skb_defer(struct sk_buff *skb)
 {
     skb_release_all(skb);
     napi_skb_cache_put(skb);
 }
 
 void napi_skb_free_stolen_head(struct sk_buff *skb)
 {
     if (unlikely(skb->slow_gro)) {
         nf_reset_ct(skb);
         skb_dst_drop(skb);
         skb_ext_put(skb);
         skb_orphan(skb);
         skb->slow_gro = 0;
     }
     napi_skb_cache_put(skb);
 }
 
 void napi_consume_skb(struct sk_buff *skb, int budget)
 {
     /* Zero budget indicate non-NAPI context called us, like netpoll */
     if (unlikely(!budget)) {
         dev_consume_skb_any(skb);
         return;
     }
 
     DEBUG_NET_WARN_ON_ONCE(!in_softirq());
 
     if (!skb_unref(skb))
         return;
 
     /* if reaching here SKB is ready to free */
     trace_consume_skb(skb);
 
     /* if SKB is a clone, don't handle this case */
     if (skb->fclone != SKB_FCLONE_UNAVAILABLE) {
         __kfree_skb(skb);
         return;
     }
 
     skb_release_all(skb);
     napi_skb_cache_put(skb);
 }
 EXPORT_SYMBOL(napi_consume_skb);
 
 /* Make sure a field is contained by headers group */
 #define CHECK_SKB_FIELD(field) \
     BUILD_BUG_ON(offsetof(struct sk_buff, field) !=     \
              offsetof(struct sk_buff, headers.field));  \
 
 static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 {
     new->tstamp     = old->tstamp;
     /* We do not copy old->sk */
     new->dev        = old->dev;
     memcpy(new->cb, old->cb, sizeof(old->cb));
     skb_dst_copy(new, old);
     __skb_ext_copy(new, old);
     __nf_copy(new, old, false);
 
     /* Note : this field could be in the headers group.
      * It is not yet because we do not want to have a 16 bit hole
      */
     new->queue_mapping = old->queue_mapping;
 
     memcpy(&new->headers, &old->headers, sizeof(new->headers));
     CHECK_SKB_FIELD(protocol);
     CHECK_SKB_FIELD(csum);
     CHECK_SKB_FIELD(hash);
     CHECK_SKB_FIELD(priority);
     CHECK_SKB_FIELD(skb_iif);
     CHECK_SKB_FIELD(vlan_proto);
     CHECK_SKB_FIELD(vlan_tci);
     CHECK_SKB_FIELD(transport_header);
     CHECK_SKB_FIELD(network_header);
     CHECK_SKB_FIELD(mac_header);
     CHECK_SKB_FIELD(inner_protocol);
     CHECK_SKB_FIELD(inner_transport_header);
     CHECK_SKB_FIELD(inner_network_header);
     CHECK_SKB_FIELD(inner_mac_header);
     CHECK_SKB_FIELD(mark);
 #ifdef CONFIG_NETWORK_SECMARK
     CHECK_SKB_FIELD(secmark);
 #endif
 #ifdef CONFIG_NET_RX_BUSY_POLL
     CHECK_SKB_FIELD(napi_id);
 #endif
     CHECK_SKB_FIELD(alloc_cpu);
 #ifdef CONFIG_XPS
     CHECK_SKB_FIELD(sender_cpu);
 #endif
 #ifdef CONFIG_NET_SCHED
     CHECK_SKB_FIELD(tc_index);
 #endif
 
 }
 
 /*
  * You should not add any new code to this function.  Add it to
  * __copy_skb_header above instead.
  */
 static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 {
 #define C(x) n->x = skb->x
 
     n->next = n->prev = NULL;
     n->sk = NULL;
     __copy_skb_header(n, skb);
 
     C(len);
     C(data_len);
     C(mac_len);
     n->hdr_len = skb->nohdr ? skb_headroom(skb) : skb->hdr_len;
     n->cloned = 1;
     n->nohdr = 0;
     n->peeked = 0;
     C(pfmemalloc);
     C(pp_recycle);
     n->destructor = NULL;
     C(tail);
     C(end);
     C(head);
     C(head_frag);
     C(data);
     C(truesize);
     refcount_set(&n->users, 1);
 
     atomic_inc(&(skb_shinfo(skb)->dataref));
     skb->cloned = 1;
 
     return n;
 #undef C
 }
 
 /**
  * alloc_skb_for_msg() - allocate sk_buff to wrap frag list forming a msg
  * @first: first sk_buff of the msg
  */
 struct sk_buff *alloc_skb_for_msg(struct sk_buff *first)
 {
     struct sk_buff *n;
 
     n = alloc_skb(0, GFP_ATOMIC);
     if (!n)
         return NULL;
 
     n->len = first->len;
     n->data_len = first->len;
     n->truesize = first->truesize;
 
     skb_shinfo(n)->frag_list = first;
 
     __copy_skb_header(n, first);
     n->destructor = NULL;
 
     return n;
 }
 EXPORT_SYMBOL_GPL(alloc_skb_for_msg);
 
 /**
  *  skb_morph   -   morph one skb into another
  *  @dst: the skb to receive the contents
  *  @src: the skb to supply the contents
  *
  *  This is identical to skb_clone except that the target skb is
  *  supplied by the user.
  *
  *  The target skb is returned upon exit.
  */
 struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
 {
     skb_release_all(dst);
     return __skb_clone(dst, src);
 }
 EXPORT_SYMBOL_GPL(skb_morph);
 
 int mm_account_pinned_pages(struct mmpin *mmp, size_t size)
 {
     unsigned long max_pg, num_pg, new_pg, old_pg;
     struct user_struct *user;
 
     if (capable(CAP_IPC_LOCK) || !size)
         return 0;
 
     num_pg = (size >> PAGE_SHIFT) + 2;  /* worst case */
     max_pg = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
     user = mmp->user ? : current_user();
 
     do {
         old_pg = atomic_long_read(&user->locked_vm);
         new_pg = old_pg + num_pg;
         if (new_pg > max_pg)
             return -ENOBUFS;
     } while (atomic_long_cmpxchg(&user->locked_vm, old_pg, new_pg) !=
          old_pg);
 
     if (!mmp->user) {
         mmp->user = get_uid(user);
         mmp->num_pg = num_pg;
     } else {
         mmp->num_pg += num_pg;
     }
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(mm_account_pinned_pages);
 
 void mm_unaccount_pinned_pages(struct mmpin *mmp)
 {
     if (mmp->user) {
         atomic_long_sub(mmp->num_pg, &mmp->user->locked_vm);
         free_uid(mmp->user);
     }
 }
 EXPORT_SYMBOL_GPL(mm_unaccount_pinned_pages);
 
 static struct ubuf_info *msg_zerocopy_alloc(struct sock *sk, size_t size)
 {
     struct ubuf_info *uarg;
     struct sk_buff *skb;
 
     WARN_ON_ONCE(!in_task());
 
     skb = sock_omalloc(sk, 0, GFP_KERNEL);
     if (!skb)
         return NULL;
 
     BUILD_BUG_ON(sizeof(*uarg) > sizeof(skb->cb));
     uarg = (void *)skb->cb;
     uarg->mmp.user = NULL;
 
     if (mm_account_pinned_pages(&uarg->mmp, size)) {
         kfree_skb(skb);
         return NULL;
     }
 
     uarg->callback = msg_zerocopy_callback;
     uarg->id = ((u32)atomic_inc_return(&sk->sk_zckey)) - 1;
     uarg->len = 1;
     uarg->bytelen = size;
     uarg->zerocopy = 1;
     uarg->flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
     refcount_set(&uarg->refcnt, 1);
     sock_hold(sk);
 
     return uarg;
 }
 
 static inline struct sk_buff *skb_from_uarg(struct ubuf_info *uarg)
 {
     return container_of((void *)uarg, struct sk_buff, cb);
 }
 
 struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
                        struct ubuf_info *uarg)
 {
     if (uarg) {
         const u32 byte_limit = 1 << 19;     /* limit to a few TSO */
         u32 bytelen, next;
 
         /* there might be non MSG_ZEROCOPY users */
         if (uarg->callback != msg_zerocopy_callback)
             return NULL;
 
         /* realloc only when socket is locked (TCP, UDP cork),
          * so uarg->len and sk_zckey access is serialized
          */
         if (!sock_owned_by_user(sk)) {
             WARN_ON_ONCE(1);
             return NULL;
         }
 
         bytelen = uarg->bytelen + size;
         if (uarg->len == USHRT_MAX - 1 || bytelen > byte_limit) {
             /* TCP can create new skb to attach new uarg */
             if (sk->sk_type == SOCK_STREAM)
                 goto new_alloc;
             return NULL;
         }
 
         next = (u32)atomic_read(&sk->sk_zckey);
         if ((u32)(uarg->id + uarg->len) == next) {
             if (mm_account_pinned_pages(&uarg->mmp, size))
                 return NULL;
             uarg->len++;
             uarg->bytelen = bytelen;
             atomic_set(&sk->sk_zckey, ++next);
 
             /* no extra ref when appending to datagram (MSG_MORE) */
             if (sk->sk_type == SOCK_STREAM)
                 net_zcopy_get(uarg);
 
             return uarg;
         }
     }
 
 new_alloc:
     return msg_zerocopy_alloc(sk, size);
 }
 EXPORT_SYMBOL_GPL(msg_zerocopy_realloc);
 
 static bool skb_zerocopy_notify_extend(struct sk_buff *skb, u32 lo, u16 len)
 {
     struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
     u32 old_lo, old_hi;
     u64 sum_len;
 
     old_lo = serr->ee.ee_info;
     old_hi = serr->ee.ee_data;
     sum_len = old_hi - old_lo + 1ULL + len;
 
     if (sum_len >= (1ULL << 32))
         return false;
 
     if (lo != old_hi + 1)
         return false;
 
     serr->ee.ee_data += len;
     return true;
 }
 
 static void __msg_zerocopy_callback(struct ubuf_info *uarg)
 {
     struct sk_buff *tail, *skb = skb_from_uarg(uarg);
     struct sock_exterr_skb *serr;
     struct sock *sk = skb->sk;
     struct sk_buff_head *q;
     unsigned long flags;
     bool is_zerocopy;
     u32 lo, hi;
     u16 len;
 
     mm_unaccount_pinned_pages(&uarg->mmp);
 
     /* if !len, there was only 1 call, and it was aborted
      * so do not queue a completion notification
      */
     if (!uarg->len || sock_flag(sk, SOCK_DEAD))
         goto release;
 
     len = uarg->len;
     lo = uarg->id;
     hi = uarg->id + len - 1;
     is_zerocopy = uarg->zerocopy;
 
     serr = SKB_EXT_ERR(skb);
     memset(serr, 0, sizeof(*serr));
     serr->ee.ee_errno = 0;
     serr->ee.ee_origin = SO_EE_ORIGIN_ZEROCOPY;
     serr->ee.ee_data = hi;
     serr->ee.ee_info = lo;
     if (!is_zerocopy)
         serr->ee.ee_code |= SO_EE_CODE_ZEROCOPY_COPIED;
 
     q = &sk->sk_error_queue;
     spin_lock_irqsave(&q->lock, flags);
     tail = skb_peek_tail(q);
     if (!tail || SKB_EXT_ERR(tail)->ee.ee_origin != SO_EE_ORIGIN_ZEROCOPY ||
         !skb_zerocopy_notify_extend(tail, lo, len)) {
         __skb_queue_tail(q, skb);
         skb = NULL;
     }
     spin_unlock_irqrestore(&q->lock, flags);
 
     sk_error_report(sk);
 
 release:
     consume_skb(skb);
     sock_put(sk);
 }
 
 void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
                bool success)
 {
     uarg->zerocopy = uarg->zerocopy & success;
 
     if (refcount_dec_and_test(&uarg->refcnt))
         __msg_zerocopy_callback(uarg);
 }
 EXPORT_SYMBOL_GPL(msg_zerocopy_callback);
 
 void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 {
     struct sock *sk = skb_from_uarg(uarg)->sk;
 
     atomic_dec(&sk->sk_zckey);
     uarg->len--;
 
     if (have_uref)
         msg_zerocopy_callback(NULL, uarg, true);
 }
 EXPORT_SYMBOL_GPL(msg_zerocopy_put_abort);
 
 int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
                  struct msghdr *msg, int len,
                  struct ubuf_info *uarg)
 {
     struct ubuf_info *orig_uarg = skb_zcopy(skb);
     int err, orig_len = skb->len;
 
     /* An skb can only point to one uarg. This edge case happens when
      * TCP appends to an skb, but zerocopy_realloc triggered a new alloc.
      */
     if (orig_uarg && uarg != orig_uarg)
         return -EEXIST;
 
     err = __zerocopy_sg_from_iter(msg, sk, skb, &msg->msg_iter, len);
     if (err == -EFAULT || (err == -EMSGSIZE && skb->len == orig_len)) {
         struct sock *save_sk = skb->sk;
 
         /* Streams do not free skb on error. Reset to prev state. */
         iov_iter_revert(&msg->msg_iter, skb->len - orig_len);
         skb->sk = sk;
         ___pskb_trim(skb, orig_len);
         skb->sk = save_sk;
         return err;
     }
 
     skb_zcopy_set(skb, uarg, NULL);
     return skb->len - orig_len;
 }
 EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);
 
 void __skb_zcopy_downgrade_managed(struct sk_buff *skb)
 {
     int i;
 
     skb_shinfo(skb)->flags &= ~SKBFL_MANAGED_FRAG_REFS;
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
         skb_frag_ref(skb, i);
 }
 EXPORT_SYMBOL_GPL(__skb_zcopy_downgrade_managed);
 
 static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
                   gfp_t gfp_mask)
 {
     if (skb_zcopy(orig)) {
         if (skb_zcopy(nskb)) {
             /* !gfp_mask callers are verified to !skb_zcopy(nskb) */
             if (!gfp_mask) {
                 WARN_ON_ONCE(1);
                 return -ENOMEM;
             }
             if (skb_uarg(nskb) == skb_uarg(orig))
                 return 0;
             if (skb_copy_ubufs(nskb, GFP_ATOMIC))
                 return -EIO;
         }
         skb_zcopy_set(nskb, skb_uarg(orig), NULL);
     }
     return 0;
 }
 
 /**
  *  skb_copy_ubufs  -   copy userspace skb frags buffers to kernel
  *  @skb: the skb to modify
  *  @gfp_mask: allocation priority
  *
  *  This must be called on skb with SKBFL_ZEROCOPY_ENABLE.
  *  It will copy all frags into kernel and drop the reference
  *  to userspace pages.
  *
  *  If this function is called from an interrupt gfp_mask() must be
  *  %GFP_ATOMIC.
  *
  *  Returns 0 on success or a negative error code on failure
  *  to allocate kernel memory to copy to.
  */
 int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
 {
     int num_frags = skb_shinfo(skb)->nr_frags;
     struct page *page, *head = NULL;
     int i, new_frags;
     u32 d_off;
 
     if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
         return -EINVAL;
 
     if (!num_frags)
         goto release;
 
     new_frags = (__skb_pagelen(skb) + PAGE_SIZE - 1) >> PAGE_SHIFT;
     for (i = 0; i < new_frags; i++) {
         page = alloc_page(gfp_mask);
         if (!page) {
             while (head) {
                 struct page *next = (struct page *)page_private(head);
                 put_page(head);
                 head = next;
             }
             return -ENOMEM;
         }
         set_page_private(page, (unsigned long)head);
         head = page;
     }
 
     page = head;
     d_off = 0;
     for (i = 0; i < num_frags; i++) {
         skb_frag_t *f = &skb_shinfo(skb)->frags[i];
         u32 p_off, p_len, copied;
         struct page *p;
         u8 *vaddr;
 
         skb_frag_foreach_page(f, skb_frag_off(f), skb_frag_size(f),
                       p, p_off, p_len, copied) {
             u32 copy, done = 0;
             vaddr = kmap_atomic(p);
 
             while (done < p_len) {
                 if (d_off == PAGE_SIZE) {
                     d_off = 0;
                     page = (struct page *)page_private(page);
                 }
                 copy = min_t(u32, PAGE_SIZE - d_off, p_len - done);
                 memcpy(page_address(page) + d_off,
                        vaddr + p_off + done, copy);
                 done += copy;
                 d_off += copy;
             }
             kunmap_atomic(vaddr);
         }
     }
 
     /* skb frags release userspace buffers */
     for (i = 0; i < num_frags; i++)
         skb_frag_unref(skb, i);
 
     /* skb frags point to kernel buffers */
     for (i = 0; i < new_frags - 1; i++) {
         __skb_fill_page_desc(skb, i, head, 0, PAGE_SIZE);
         head = (struct page *)page_private(head);
     }
     __skb_fill_page_desc(skb, new_frags - 1, head, 0, d_off);
     skb_shinfo(skb)->nr_frags = new_frags;
 
 release:
     skb_zcopy_clear(skb, false);
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_copy_ubufs);
 
 /**
  *  skb_clone   -   duplicate an sk_buff
  *  @skb: buffer to clone
  *  @gfp_mask: allocation priority
  *
  *  Duplicate an &sk_buff. The new one is not owned by a socket. Both
  *  copies share the same packet data but not structure. The new
  *  buffer has a reference count of 1. If the allocation fails the
  *  function returns %NULL otherwise the new buffer is returned.
  *
  *  If this function is called from an interrupt gfp_mask() must be
  *  %GFP_ATOMIC.
  */
 
 struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
 {
     struct sk_buff_fclones *fclones = container_of(skb,
                                struct sk_buff_fclones,
                                skb1);
     struct sk_buff *n;
 
     if (skb_orphan_frags(skb, gfp_mask))
         return NULL;
 
     if (skb->fclone == SKB_FCLONE_ORIG &&
         refcount_read(&fclones->fclone_ref) == 1) {
         n = &fclones->skb2;
         refcount_set(&fclones->fclone_ref, 2);
         n->fclone = SKB_FCLONE_CLONE;
     } else {
         if (skb_pfmemalloc(skb))
             gfp_mask |= __GFP_MEMALLOC;
 
         n = kmem_cache_alloc(skbuff_head_cache, gfp_mask);
         if (!n)
             return NULL;
 
         n->fclone = SKB_FCLONE_UNAVAILABLE;
     }
 
     return __skb_clone(n, skb);
 }
 EXPORT_SYMBOL(skb_clone);
 
 void skb_headers_offset_update(struct sk_buff *skb, int off)
 {
     /* Only adjust this if it actually is csum_start rather than csum */
     if (skb->ip_summed == CHECKSUM_PARTIAL)
         skb->csum_start += off;
     /* {transport,network,mac}_header and tail are relative to skb->head */
     skb->transport_header += off;
     skb->network_header   += off;
     if (skb_mac_header_was_set(skb))
         skb->mac_header += off;
     skb->inner_transport_header += off;
     skb->inner_network_header += off;
     skb->inner_mac_header += off;
 }
 EXPORT_SYMBOL(skb_headers_offset_update);
 
 void skb_copy_header(struct sk_buff *new, const struct sk_buff *old)
 {
     __copy_skb_header(new, old);
 
     skb_shinfo(new)->gso_size = skb_shinfo(old)->gso_size;
     skb_shinfo(new)->gso_segs = skb_shinfo(old)->gso_segs;
     skb_shinfo(new)->gso_type = skb_shinfo(old)->gso_type;
 }
 EXPORT_SYMBOL(skb_copy_header);
 
 static inline int skb_alloc_rx_flag(const struct sk_buff *skb)
 {
     if (skb_pfmemalloc(skb))
         return SKB_ALLOC_RX;
     return 0;
 }
 
 /**
  *  skb_copy    -   create private copy of an sk_buff
  *  @skb: buffer to copy
  *  @gfp_mask: allocation priority
  *
  *  Make a copy of both an &sk_buff and its data. This is used when the
  *  caller wishes to modify the data and needs a private copy of the
  *  data to alter. Returns %NULL on failure or the pointer to the buffer
  *  on success. The returned buffer has a reference count of 1.
  *
  *  As by-product this function converts non-linear &sk_buff to linear
  *  one, so that &sk_buff becomes completely private and caller is allowed
  *  to modify all the data of returned buffer. This means that this
  *  function is not recommended for use in circumstances when only
  *  header is going to be modified. Use pskb_copy() instead.
  */
 
 struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
 {
     int headerlen = skb_headroom(skb);
     unsigned int size = skb_end_offset(skb) + skb->data_len;
     struct sk_buff *n = __alloc_skb(size, gfp_mask,
                     skb_alloc_rx_flag(skb), NUMA_NO_NODE);
 
     if (!n)
         return NULL;
 
     /* Set the data pointer */
     skb_reserve(n, headerlen);
     /* Set the tail pointer and length */
     skb_put(n, skb->len);
 
     BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));
 
     skb_copy_header(n, skb);
     return n;
 }
 EXPORT_SYMBOL(skb_copy);
 
 /**
  *  __pskb_copy_fclone  -  create copy of an sk_buff with private head.
  *  @skb: buffer to copy
  *  @headroom: headroom of new skb
  *  @gfp_mask: allocation priority
  *  @fclone: if true allocate the copy of the skb from the fclone
  *  cache instead of the head cache; it is recommended to set this
  *  to true for the cases where the copy will likely be cloned
  *
  *  Make a copy of both an &sk_buff and part of its data, located
  *  in header. Fragmented data remain shared. This is used when
  *  the caller wishes to modify only header of &sk_buff and needs
  *  private copy of the header to alter. Returns %NULL on failure
  *  or the pointer to the buffer on success.
  *  The returned buffer has a reference count of 1.
  */
 
 struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
                    gfp_t gfp_mask, bool fclone)
 {
     unsigned int size = skb_headlen(skb) + headroom;
     int flags = skb_alloc_rx_flag(skb) | (fclone ? SKB_ALLOC_FCLONE : 0);
     struct sk_buff *n = __alloc_skb(size, gfp_mask, flags, NUMA_NO_NODE);
 
     if (!n)
         goto out;
 
     /* Set the data pointer */
     skb_reserve(n, headroom);
     /* Set the tail pointer and length */
     skb_put(n, skb_headlen(skb));
     /* Copy the bytes */
     skb_copy_from_linear_data(skb, n->data, n->len);
 
     n->truesize += skb->data_len;
     n->data_len  = skb->data_len;
     n->len       = skb->len;
 
     if (skb_shinfo(skb)->nr_frags) {
         int i;
 
         if (skb_orphan_frags(skb, gfp_mask) ||
             skb_zerocopy_clone(n, skb, gfp_mask)) {
             kfree_skb(n);
             n = NULL;
             goto out;
         }
         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
             skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
             skb_frag_ref(skb, i);
         }
         skb_shinfo(n)->nr_frags = i;
     }
 
     if (skb_has_frag_list(skb)) {
         skb_shinfo(n)->frag_list = skb_shinfo(skb)->frag_list;
         skb_clone_fraglist(n);
     }
 
     skb_copy_header(n, skb);
 out:
     return n;
 }
 EXPORT_SYMBOL(__pskb_copy_fclone);
 
 /**
  *  pskb_expand_head - reallocate header of &sk_buff
  *  @skb: buffer to reallocate
  *  @nhead: room to add at head
  *  @ntail: room to add at tail
  *  @gfp_mask: allocation priority
  *
  *  Expands (or creates identical copy, if @nhead and @ntail are zero)
  *  header of @skb. &sk_buff itself is not changed. &sk_buff MUST have
  *  reference count of 1. Returns zero in the case of success or error,
  *  if expansion failed. In the last case, &sk_buff is not changed.
  *
  *  All the pointers pointing into skb header may change and must be
  *  reloaded after call to this function.
  */
 
 int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
              gfp_t gfp_mask)
 {
     int i, osize = skb_end_offset(skb);
     int size = osize + nhead + ntail;
     long off;
     u8 *data;
 
     BUG_ON(nhead < 0);
 
     BUG_ON(skb_shared(skb));
 
     skb_zcopy_downgrade_managed(skb);
 
     size = SKB_DATA_ALIGN(size);
 
     if (skb_pfmemalloc(skb))
         gfp_mask |= __GFP_MEMALLOC;
     data = kmalloc_reserve(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                    gfp_mask, NUMA_NO_NODE, NULL);
     if (!data)
         goto nodata;
     size = SKB_WITH_OVERHEAD(ksize(data));
 
     /* Copy only real data... and, alas, header. This should be
      * optimized for the cases when header is void.
      */
     memcpy(data + nhead, skb->head, skb_tail_pointer(skb) - skb->head);
 
     memcpy((struct skb_shared_info *)(data + size),
            skb_shinfo(skb),
            offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
 
     /*
      * if shinfo is shared we must drop the old head gracefully, but if it
      * is not we can just drop the old head and let the existing refcount
      * be since all we did is relocate the values
      */
     if (skb_cloned(skb)) {
         if (skb_orphan_frags(skb, gfp_mask))
             goto nofrags;
         if (skb_zcopy(skb))
             refcount_inc(&skb_uarg(skb)->refcnt);
         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
             skb_frag_ref(skb, i);
 
         if (skb_has_frag_list(skb))
             skb_clone_fraglist(skb);
 
         skb_release_data(skb);
     } else {
         skb_free_head(skb);
     }
     off = (data + nhead) - skb->head;
 
     skb->head     = data;
     skb->head_frag = 0;
     skb->data    += off;
 
     skb_set_end_offset(skb, size);
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
     off           = nhead;
 #endif
     skb->tail         += off;
     skb_headers_offset_update(skb, nhead);
     skb->cloned   = 0;
     skb->hdr_len  = 0;
     skb->nohdr    = 0;
     atomic_set(&skb_shinfo(skb)->dataref, 1);
 
     skb_metadata_clear(skb);
 
     /* It is not generally safe to change skb->truesize.
      * For the moment, we really care of rx path, or
      * when skb is orphaned (not attached to a socket).
      */
     if (!skb->sk || skb->destructor == sock_edemux)
         skb->truesize += size - osize;
 
     return 0;
 
 nofrags:
     kfree(data);
 nodata:
     return -ENOMEM;
 }
 EXPORT_SYMBOL(pskb_expand_head);
 
 /* Make private copy of skb with writable head and some headroom */
 
 struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)
 {
     struct sk_buff *skb2;
     int delta = headroom - skb_headroom(skb);
 
     if (delta <= 0)
         skb2 = pskb_copy(skb, GFP_ATOMIC);
     else {
         skb2 = skb_clone(skb, GFP_ATOMIC);
         if (skb2 && pskb_expand_head(skb2, SKB_DATA_ALIGN(delta), 0,
                          GFP_ATOMIC)) {
             kfree_skb(skb2);
             skb2 = NULL;
         }
     }
     return skb2;
 }
 EXPORT_SYMBOL(skb_realloc_headroom);
 
 int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
 {
     unsigned int saved_end_offset, saved_truesize;
     struct skb_shared_info *shinfo;
     int res;
 
     saved_end_offset = skb_end_offset(skb);
     saved_truesize = skb->truesize;
 
     res = pskb_expand_head(skb, 0, 0, pri);
     if (res)
         return res;
 
     skb->truesize = saved_truesize;
 
     if (likely(skb_end_offset(skb) == saved_end_offset))
         return 0;
 
     shinfo = skb_shinfo(skb);
 
     /* We are about to change back skb->end,
      * we need to move skb_shinfo() to its new location.
      */
     memmove(skb->head + saved_end_offset,
         shinfo,
         offsetof(struct skb_shared_info, frags[shinfo->nr_frags]));
 
     skb_set_end_offset(skb, saved_end_offset);
 
     return 0;
 }
 
 /**
  *  skb_expand_head - reallocate header of &sk_buff
  *  @skb: buffer to reallocate
  *  @headroom: needed headroom
  *
  *  Unlike skb_realloc_headroom, this one does not allocate a new skb
  *  if possible; copies skb->sk to new skb as needed
  *  and frees original skb in case of failures.
  *
  *  It expect increased headroom and generates warning otherwise.
  */
 
 struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
 {
     int delta = headroom - skb_headroom(skb);
     int osize = skb_end_offset(skb);
     struct sock *sk = skb->sk;
 
     if (WARN_ONCE(delta <= 0,
               "%s is expecting an increase in the headroom", __func__))
         return skb;
 
     delta = SKB_DATA_ALIGN(delta);
     /* pskb_expand_head() might crash, if skb is shared. */
     if (skb_shared(skb) || !is_skb_wmem(skb)) {
         struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
 
         if (unlikely(!nskb))
             goto fail;
 
         if (sk)
             skb_set_owner_w(nskb, sk);
         consume_skb(skb);
         skb = nskb;
     }
     if (pskb_expand_head(skb, delta, 0, GFP_ATOMIC))
         goto fail;
 
     if (sk && is_skb_wmem(skb)) {
         delta = skb_end_offset(skb) - osize;
         refcount_add(delta, &sk->sk_wmem_alloc);
         skb->truesize += delta;
     }
     return skb;
 
 fail:
     kfree_skb(skb);
     return NULL;
 }
 EXPORT_SYMBOL(skb_expand_head);
 
 /**
  *  skb_copy_expand -   copy and expand sk_buff
  *  @skb: buffer to copy
  *  @newheadroom: new free bytes at head
  *  @newtailroom: new free bytes at tail
  *  @gfp_mask: allocation priority
  *
  *  Make a copy of both an &sk_buff and its data and while doing so
  *  allocate additional space.
  *
  *  This is used when the caller wishes to modify the data and needs a
  *  private copy of the data to alter as well as more space for new fields.
  *  Returns %NULL on failure or the pointer to the buffer
  *  on success. The returned buffer has a reference count of 1.
  *
  *  You must pass %GFP_ATOMIC as the allocation priority if this function
  *  is called from an interrupt.
  */
 struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
                 int newheadroom, int newtailroom,
                 gfp_t gfp_mask)
 {
     /*
      *  Allocate the copy buffer
      */
     struct sk_buff *n = __alloc_skb(newheadroom + skb->len + newtailroom,
                     gfp_mask, skb_alloc_rx_flag(skb),
                     NUMA_NO_NODE);
     int oldheadroom = skb_headroom(skb);
     int head_copy_len, head_copy_off;
 
     if (!n)
         return NULL;
 
     skb_reserve(n, newheadroom);
 
     /* Set the tail pointer and length */
     skb_put(n, skb->len);
 
     head_copy_len = oldheadroom;
     head_copy_off = 0;
     if (newheadroom <= head_copy_len)
         head_copy_len = newheadroom;
     else
         head_copy_off = newheadroom - head_copy_len;
 
     /* Copy the linear header and data. */
     BUG_ON(skb_copy_bits(skb, -head_copy_len, n->head + head_copy_off,
                  skb->len + head_copy_len));
 
     skb_copy_header(n, skb);
 
     skb_headers_offset_update(n, newheadroom - oldheadroom);
 
     return n;
 }
 EXPORT_SYMBOL(skb_copy_expand);
 
 /**
  *  __skb_pad       -   zero pad the tail of an skb
  *  @skb: buffer to pad
  *  @pad: space to pad
  *  @free_on_error: free buffer on error
  *
  *  Ensure that a buffer is followed by a padding area that is zero
  *  filled. Used by network drivers which may DMA or transfer data
  *  beyond the buffer end onto the wire.
  *
  *  May return error in out of memory cases. The skb is freed on error
  *  if @free_on_error is true.
  */
 
 int __skb_pad(struct sk_buff *skb, int pad, bool free_on_error)
 {
     int err;
     int ntail;
 
     /* If the skbuff is non linear tailroom is always zero.. */
     if (!skb_cloned(skb) && skb_tailroom(skb) >= pad) {
         memset(skb->data+skb->len, 0, pad);
         return 0;
     }
 
     ntail = skb->data_len + pad - (skb->end - skb->tail);
     if (likely(skb_cloned(skb) || ntail > 0)) {
         err = pskb_expand_head(skb, 0, ntail, GFP_ATOMIC);
         if (unlikely(err))
             goto free_skb;
     }
 
     /* FIXME: The use of this function with non-linear skb's really needs
      * to be audited.
      */
     err = skb_linearize(skb);
     if (unlikely(err))
         goto free_skb;
 
     memset(skb->data + skb->len, 0, pad);
     return 0;
 
 free_skb:
     if (free_on_error)
         kfree_skb(skb);
     return err;
 }
 EXPORT_SYMBOL(__skb_pad);
 
 /**
  *  pskb_put - add data to the tail of a potentially fragmented buffer
  *  @skb: start of the buffer to use
  *  @tail: tail fragment of the buffer to use
  *  @len: amount of data to add
  *
  *  This function extends the used data area of the potentially
  *  fragmented buffer. @tail must be the last fragment of @skb -- or
  *  @skb itself. If this would exceed the total buffer size the kernel
  *  will panic. A pointer to the first byte of the extra data is
  *  returned.
  */
 
 void *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len)
 {
     if (tail != skb) {
         skb->data_len += len;
         skb->len += len;
     }
     return skb_put(tail, len);
 }
 EXPORT_SYMBOL_GPL(pskb_put);
 
 /**
  *  skb_put - add data to a buffer
  *  @skb: buffer to use
  *  @len: amount of data to add
  *
  *  This function extends the used data area of the buffer. If this would
  *  exceed the total buffer size the kernel will panic. A pointer to the
  *  first byte of the extra data is returned.
  */
 void *skb_put(struct sk_buff *skb, unsigned int len)
 {
     void *tmp = skb_tail_pointer(skb);
     SKB_LINEAR_ASSERT(skb);
     skb->tail += len;
     skb->len  += len;
     if (unlikely(skb->tail > skb->end))
         skb_over_panic(skb, len, __builtin_return_address(0));
     return tmp;
 }
 EXPORT_SYMBOL(skb_put);
 
 /**
  *  skb_push - add data to the start of a buffer
  *  @skb: buffer to use
  *  @len: amount of data to add
  *
  *  This function extends the used data area of the buffer at the buffer
  *  start. If this would exceed the total buffer headroom the kernel will
  *  panic. A pointer to the first byte of the extra data is returned.
  */
 void *skb_push(struct sk_buff *skb, unsigned int len)
 {
     skb->data -= len;
     skb->len  += len;
     if (unlikely(skb->data < skb->head))
         skb_under_panic(skb, len, __builtin_return_address(0));
     return skb->data;
 }
 EXPORT_SYMBOL(skb_push);
 
 /**
  *  skb_pull - remove data from the start of a buffer
  *  @skb: buffer to use
  *  @len: amount of data to remove
  *
  *  This function removes data from the start of a buffer, returning
  *  the memory to the headroom. A pointer to the next data in the buffer
  *  is returned. Once the data has been pulled future pushes will overwrite
  *  the old data.
  */
 void *skb_pull(struct sk_buff *skb, unsigned int len)
 {
     return skb_pull_inline(skb, len);
 }
 EXPORT_SYMBOL(skb_pull);
 
 /**
  *  skb_pull_data - remove data from the start of a buffer returning its
  *  original position.
  *  @skb: buffer to use
  *  @len: amount of data to remove
  *
  *  This function removes data from the start of a buffer, returning
  *  the memory to the headroom. A pointer to the original data in the buffer
  *  is returned after checking if there is enough data to pull. Once the
  *  data has been pulled future pushes will overwrite the old data.
  */
 void *skb_pull_data(struct sk_buff *skb, size_t len)
 {
     void *data = skb->data;
 
     if (skb->len < len)
         return NULL;
 
     skb_pull(skb, len);
 
     return data;
 }
 EXPORT_SYMBOL(skb_pull_data);
 
 /**
  *  skb_trim - remove end from a buffer
  *  @skb: buffer to alter
  *  @len: new length
  *
  *  Cut the length of a buffer down by removing data from the tail. If
  *  the buffer is already under the length specified it is not modified.
  *  The skb must be linear.
  */
 void skb_trim(struct sk_buff *skb, unsigned int len)
 {
     if (skb->len > len)
         __skb_trim(skb, len);
 }
 EXPORT_SYMBOL(skb_trim);
 
 /* Trims skb to length len. It can change skb pointers.
  */
 
 int ___pskb_trim(struct sk_buff *skb, unsigned int len)
 {
     struct sk_buff **fragp;
     struct sk_buff *frag;
     int offset = skb_headlen(skb);
     int nfrags = skb_shinfo(skb)->nr_frags;
     int i;
     int err;
 
     if (skb_cloned(skb) &&
         unlikely((err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC))))
         return err;
 
     i = 0;
     if (offset >= len)
         goto drop_pages;
 
     for (; i < nfrags; i++) {
         int end = offset + skb_frag_size(&skb_shinfo(skb)->frags[i]);
 
         if (end < len) {
             offset = end;
             continue;
         }
 
         skb_frag_size_set(&skb_shinfo(skb)->frags[i++], len - offset);
 
 drop_pages:
         skb_shinfo(skb)->nr_frags = i;
 
         for (; i < nfrags; i++)
             skb_frag_unref(skb, i);
 
         if (skb_has_frag_list(skb))
             skb_drop_fraglist(skb);
         goto done;
     }
 
     for (fragp = &skb_shinfo(skb)->frag_list; (frag = *fragp);
          fragp = &frag->next) {
         int end = offset + frag->len;
 
         if (skb_shared(frag)) {
             struct sk_buff *nfrag;
 
             nfrag = skb_clone(frag, GFP_ATOMIC);
             if (unlikely(!nfrag))
                 return -ENOMEM;
 
             nfrag->next = frag->next;
             consume_skb(frag);
             frag = nfrag;
             *fragp = frag;
         }
 
         if (end < len) {
             offset = end;
             continue;
         }
 
         if (end > len &&
             unlikely((err = pskb_trim(frag, len - offset))))
             return err;
 
         if (frag->next)
             skb_drop_list(&frag->next);
         break;
     }
 
 done:
     if (len > skb_headlen(skb)) {
         skb->data_len -= skb->len - len;
         skb->len       = len;
     } else {
         skb->len       = len;
         skb->data_len  = 0;
         skb_set_tail_pointer(skb, len);
     }
 
     if (!skb->sk || skb->destructor == sock_edemux)
         skb_condense(skb);
     return 0;
 }
 EXPORT_SYMBOL(___pskb_trim);
 
 /* Note : use pskb_trim_rcsum() instead of calling this directly
  */
 int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE) {
         int delta = skb->len - len;
 
         skb->csum = csum_block_sub(skb->csum,
                        skb_checksum(skb, len, delta, 0),
                        len);
     } else if (skb->ip_summed == CHECKSUM_PARTIAL) {
         int hdlen = (len > skb_headlen(skb)) ? skb_headlen(skb) : len;
         int offset = skb_checksum_start_offset(skb) + skb->csum_offset;
 
         if (offset + sizeof(__sum16) > hdlen)
             return -EINVAL;
     }
     return __pskb_trim(skb, len);
 }
 EXPORT_SYMBOL(pskb_trim_rcsum_slow);
 
 /**
  *  __pskb_pull_tail - advance tail of skb header
  *  @skb: buffer to reallocate
  *  @delta: number of bytes to advance tail
  *
  *  The function makes a sense only on a fragmented &sk_buff,
  *  it expands header moving its tail forward and copying necessary
  *  data from fragmented part.
  *
  *  &sk_buff MUST have reference count of 1.
  *
  *  Returns %NULL (and &sk_buff does not change) if pull failed
  *  or value of new tail of skb in the case of success.
  *
  *  All the pointers pointing into skb header may change and must be
  *  reloaded after call to this function.
  */
 
 /* Moves tail of skb head forward, copying data from fragmented part,
  * when it is necessary.
  * 1. It may fail due to malloc failure.
  * 2. It may change skb pointers.
  *
  * It is pretty complicated. Luckily, it is called only in exceptional cases.
  */
 void *__pskb_pull_tail(struct sk_buff *skb, int delta)
 {
     /* If skb has not enough free space at tail, get new one
      * plus 128 bytes for future expansions. If we have enough
      * room at tail, reallocate without expansion only if skb is cloned.
      */
     int i, k, eat = (skb->tail + delta) - skb->end;
 
     if (eat > 0 || skb_cloned(skb)) {
         if (pskb_expand_head(skb, 0, eat > 0 ? eat + 128 : 0,
                      GFP_ATOMIC))
             return NULL;
     }
 
     BUG_ON(skb_copy_bits(skb, skb_headlen(skb),
                  skb_tail_pointer(skb), delta));
 
     /* Optimization: no fragments, no reasons to preestimate
      * size of pulled pages. Superb.
      */
     if (!skb_has_frag_list(skb))
         goto pull_pages;
 
     /* Estimate size of pulled pages. */
     eat = delta;
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 
         if (size >= eat)
             goto pull_pages;
         eat -= size;
     }
 
     /* If we need update frag list, we are in troubles.
      * Certainly, it is possible to add an offset to skb data,
      * but taking into account that pulling is expected to
      * be very rare operation, it is worth to fight against
      * further bloating skb head and crucify ourselves here instead.
      * Pure masohism, indeed. 8)8)
      */
     if (eat) {
         struct sk_buff *list = skb_shinfo(skb)->frag_list;
         struct sk_buff *clone = NULL;
         struct sk_buff *insp = NULL;
 
         do {
             if (list->len <= eat) {
                 /* Eaten as whole. */
                 eat -= list->len;
                 list = list->next;
                 insp = list;
             } else {
                 /* Eaten partially. */
 
                 if (skb_shared(list)) {
                     /* Sucks! We need to fork list. :-( */
                     clone = skb_clone(list, GFP_ATOMIC);
                     if (!clone)
                         return NULL;
                     insp = list->next;
                     list = clone;
                 } else {
                     /* This may be pulled without
                      * problems. */
                     insp = list;
                 }
                 if (!pskb_pull(list, eat)) {
                     kfree_skb(clone);
                     return NULL;
                 }
                 break;
             }
         } while (eat);
 
         /* Free pulled out fragments. */
         while ((list = skb_shinfo(skb)->frag_list) != insp) {
             skb_shinfo(skb)->frag_list = list->next;
             consume_skb(list);
         }
         /* And insert new clone at head. */
         if (clone) {
             clone->next = list;
             skb_shinfo(skb)->frag_list = clone;
         }
     }
     /* Success! Now we may commit changes to skb data. */
 
 pull_pages:
     eat = delta;
     k = 0;
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 
         if (size <= eat) {
             skb_frag_unref(skb, i);
             eat -= size;
         } else {
             skb_frag_t *frag = &skb_shinfo(skb)->frags[k];
 
             *frag = skb_shinfo(skb)->frags[i];
             if (eat) {
                 skb_frag_off_add(frag, eat);
                 skb_frag_size_sub(frag, eat);
                 if (!i)
                     goto end;
                 eat = 0;
             }
             k++;
         }
     }
     skb_shinfo(skb)->nr_frags = k;
 
 end:
     skb->tail     += delta;
     skb->data_len -= delta;
 
     if (!skb->data_len)
         skb_zcopy_clear(skb, false);
 
     return skb_tail_pointer(skb);
 }
 EXPORT_SYMBOL(__pskb_pull_tail);
 
 /**
  *  skb_copy_bits - copy bits from skb to kernel buffer
  *  @skb: source skb
  *  @offset: offset in source
  *  @to: destination buffer
  *  @len: number of bytes to copy
  *
  *  Copy the specified number of bytes from the source skb to the
  *  destination buffer.
  *
  *  CAUTION ! :
  *      If its prototype is ever changed,
  *      check arch/{*}/net/{*}.S files,
  *      since it is called from BPF assembly code.
  */
 int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
 {
     int start = skb_headlen(skb);
     struct sk_buff *frag_iter;
     int i, copy;
 
     if (offset > (int)skb->len - len)
         goto fault;
 
     /* Copy header. */
     if ((copy = start - offset) > 0) {
         if (copy > len)
             copy = len;
         skb_copy_from_linear_data_offset(skb, offset, to, copy);
         if ((len -= copy) == 0)
             return 0;
         offset += copy;
         to     += copy;
     }
 
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int end;
         skb_frag_t *f = &skb_shinfo(skb)->frags[i];
 
         WARN_ON(start > offset + len);
 
         end = start + skb_frag_size(f);
         if ((copy = end - offset) > 0) {
             u32 p_off, p_len, copied;
             struct page *p;
             u8 *vaddr;
 
             if (copy > len)
                 copy = len;
 
             skb_frag_foreach_page(f,
                           skb_frag_off(f) + offset - start,
                           copy, p, p_off, p_len, copied) {
                 vaddr = kmap_atomic(p);
                 memcpy(to + copied, vaddr + p_off, p_len);
                 kunmap_atomic(vaddr);
             }
 
             if ((len -= copy) == 0)
                 return 0;
             offset += copy;
             to     += copy;
         }
         start = end;
     }
 
     skb_walk_frags(skb, frag_iter) {
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + frag_iter->len;
         if ((copy = end - offset) > 0) {
             if (copy > len)
                 copy = len;
             if (skb_copy_bits(frag_iter, offset - start, to, copy))
                 goto fault;
             if ((len -= copy) == 0)
                 return 0;
             offset += copy;
             to     += copy;
         }
         start = end;
     }
 
     if (!len)
         return 0;
 
 fault:
     return -EFAULT;
 }
 EXPORT_SYMBOL(skb_copy_bits);
 
 /*
  * Callback from splice_to_pipe(), if we need to release some pages
  * at the end of the spd in case we error'ed out in filling the pipe.
  */
 static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
 {
     put_page(spd->pages[i]);
 }
 
 static struct page *linear_to_page(struct page *page, unsigned int *len,
                    unsigned int *offset,
                    struct sock *sk)
 {
     struct page_frag *pfrag = sk_page_frag(sk);
 
     if (!sk_page_frag_refill(sk, pfrag))
         return NULL;
 
     *len = min_t(unsigned int, *len, pfrag->size - pfrag->offset);
 
     memcpy(page_address(pfrag->page) + pfrag->offset,
            page_address(page) + *offset, *len);
     *offset = pfrag->offset;
     pfrag->offset += *len;
 
     return pfrag->page;
 }
 
 static bool spd_can_coalesce(const struct splice_pipe_desc *spd,
                  struct page *page,
                  unsigned int offset)
 {
     return  spd->nr_pages &&
         spd->pages[spd->nr_pages - 1] == page &&
         (spd->partial[spd->nr_pages - 1].offset +
          spd->partial[spd->nr_pages - 1].len == offset);
 }
 
 /*
  * Fill page/offset/length into spd, if it can hold more pages.
  */
 static bool spd_fill_page(struct splice_pipe_desc *spd,
               struct pipe_inode_info *pipe, struct page *page,
               unsigned int *len, unsigned int offset,
               bool linear,
               struct sock *sk)
 {
     if (unlikely(spd->nr_pages == MAX_SKB_FRAGS))
         return true;
 
     if (linear) {
         page = linear_to_page(page, len, &offset, sk);
         if (!page)
             return true;
     }
     if (spd_can_coalesce(spd, page, offset)) {
         spd->partial[spd->nr_pages - 1].len += *len;
         return false;
     }
     get_page(page);
     spd->pages[spd->nr_pages] = page;
     spd->partial[spd->nr_pages].len = *len;
     spd->partial[spd->nr_pages].offset = offset;
     spd->nr_pages++;
 
     return false;
 }
 
 static bool __splice_segment(struct page *page, unsigned int poff,
                  unsigned int plen, unsigned int *off,
                  unsigned int *len,
                  struct splice_pipe_desc *spd, bool linear,
                  struct sock *sk,
                  struct pipe_inode_info *pipe)
 {
     if (!*len)
         return true;
 
     /* skip this segment if already processed */
     if (*off >= plen) {
         *off -= plen;
         return false;
     }
 
     /* ignore any bits we already processed */
     poff += *off;
     plen -= *off;
     *off = 0;
 
     do {
         unsigned int flen = min(*len, plen);
 
         if (spd_fill_page(spd, pipe, page, &flen, poff,
                   linear, sk))
             return true;
         poff += flen;
         plen -= flen;
         *len -= flen;
     } while (*len && plen);
 
     return false;
 }
 
 /*
  * Map linear and fragment data from the skb to spd. It reports true if the
  * pipe is full or if we already spliced the requested length.
  */
 static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
                   unsigned int *offset, unsigned int *len,
                   struct splice_pipe_desc *spd, struct sock *sk)
 {
     int seg;
     struct sk_buff *iter;
 
     /* map the linear part :
      * If skb->head_frag is set, this 'linear' part is backed by a
      * fragment, and if the head is not shared with any clones then
      * we can avoid a copy since we own the head portion of this page.
      */
     if (__splice_segment(virt_to_page(skb->data),
                  (unsigned long) skb->data & (PAGE_SIZE - 1),
                  skb_headlen(skb),
                  offset, len, spd,
                  skb_head_is_locked(skb),
                  sk, pipe))
         return true;
 
     /*
      * then map the fragments
      */
     for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {
         const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];
 
         if (__splice_segment(skb_frag_page(f),
                      skb_frag_off(f), skb_frag_size(f),
                      offset, len, spd, false, sk, pipe))
             return true;
     }
 
     skb_walk_frags(skb, iter) {
         if (*offset >= iter->len) {
             *offset -= iter->len;
             continue;
         }
         /* __skb_splice_bits() only fails if the output has no room
          * left, so no point in going over the frag_list for the error
          * case.
          */
         if (__skb_splice_bits(iter, pipe, offset, len, spd, sk))
             return true;
     }
 
     return false;
 }
 
 /*
  * Map data from the skb to a pipe. Should handle both the linear part,
  * the fragments, and the frag list.
  */
 int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
             struct pipe_inode_info *pipe, unsigned int tlen,
             unsigned int flags)
 {
     struct partial_page partial[MAX_SKB_FRAGS];
     struct page *pages[MAX_SKB_FRAGS];
     struct splice_pipe_desc spd = {
         .pages = pages,
         .partial = partial,
         .nr_pages_max = MAX_SKB_FRAGS,
         .ops = &nosteal_pipe_buf_ops,
         .spd_release = sock_spd_release,
     };
     int ret = 0;
 
     __skb_splice_bits(skb, pipe, &offset, &tlen, &spd, sk);
 
     if (spd.nr_pages)
         ret = splice_to_pipe(pipe, &spd);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(skb_splice_bits);
 
 static int sendmsg_unlocked(struct sock *sk, struct msghdr *msg,
                 struct kvec *vec, size_t num, size_t size)
 {
     struct socket *sock = sk->sk_socket;
 
     if (!sock)
         return -EINVAL;
     return kernel_sendmsg(sock, msg, vec, num, size);
 }
 
 static int sendpage_unlocked(struct sock *sk, struct page *page, int offset,
                  size_t size, int flags)
 {
     struct socket *sock = sk->sk_socket;
 
     if (!sock)
         return -EINVAL;
     return kernel_sendpage(sock, page, offset, size, flags);
 }
 
 typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg,
                 struct kvec *vec, size_t num, size_t size);
 typedef int (*sendpage_func)(struct sock *sk, struct page *page, int offset,
                  size_t size, int flags);
 static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
                int len, sendmsg_func sendmsg, sendpage_func sendpage)
 {
     unsigned int orig_len = len;
     struct sk_buff *head = skb;
     unsigned short fragidx;
     int slen, ret;
 
 do_frag_list:
 
     /* Deal with head data */
     while (offset < skb_headlen(skb) && len) {
         struct kvec kv;
         struct msghdr msg;
 
         slen = min_t(int, len, skb_headlen(skb) - offset);
         kv.iov_base = skb->data + offset;
         kv.iov_len = slen;
         memset(&msg, 0, sizeof(msg));
         msg.msg_flags = MSG_DONTWAIT;
 
         ret = INDIRECT_CALL_2(sendmsg, kernel_sendmsg_locked,
                       sendmsg_unlocked, sk, &msg, &kv, 1, slen);
         if (ret <= 0)
             goto error;
 
         offset += ret;
         len -= ret;
     }
 
     /* All the data was skb head? */
     if (!len)
         goto out;
 
     /* Make offset relative to start of frags */
     offset -= skb_headlen(skb);
 
     /* Find where we are in frag list */
     for (fragidx = 0; fragidx < skb_shinfo(skb)->nr_frags; fragidx++) {
         skb_frag_t *frag  = &skb_shinfo(skb)->frags[fragidx];
 
         if (offset < skb_frag_size(frag))
             break;
 
         offset -= skb_frag_size(frag);
     }
 
     for (; len && fragidx < skb_shinfo(skb)->nr_frags; fragidx++) {
         skb_frag_t *frag  = &skb_shinfo(skb)->frags[fragidx];
 
         slen = min_t(size_t, len, skb_frag_size(frag) - offset);
 
         while (slen) {
             ret = INDIRECT_CALL_2(sendpage, kernel_sendpage_locked,
                           sendpage_unlocked, sk,
                           skb_frag_page(frag),
                           skb_frag_off(frag) + offset,
                           slen, MSG_DONTWAIT);
             if (ret <= 0)
                 goto error;
 
             len -= ret;
             offset += ret;
             slen -= ret;
         }
 
         offset = 0;
     }
 
     if (len) {
         /* Process any frag lists */
 
         if (skb == head) {
             if (skb_has_frag_list(skb)) {
                 skb = skb_shinfo(skb)->frag_list;
                 goto do_frag_list;
             }
         } else if (skb->next) {
             skb = skb->next;
             goto do_frag_list;
         }
     }
 
 out:
     return orig_len - len;
 
 error:
     return orig_len == len ? ret : orig_len - len;
 }
 
 /* Send skb data on a socket. Socket must be locked. */
 int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
              int len)
 {
     return __skb_send_sock(sk, skb, offset, len, kernel_sendmsg_locked,
                    kernel_sendpage_locked);
 }
 EXPORT_SYMBOL_GPL(skb_send_sock_locked);
 
 /* Send skb data on a socket. Socket must be unlocked. */
 int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len)
 {
     return __skb_send_sock(sk, skb, offset, len, sendmsg_unlocked,
                    sendpage_unlocked);
 }
 
 /**
  *  skb_store_bits - store bits from kernel buffer to skb
  *  @skb: destination buffer
  *  @offset: offset in destination
  *  @from: source buffer
  *  @len: number of bytes to copy
  *
  *  Copy the specified number of bytes from the source buffer to the
  *  destination skb.  This function handles all the messy bits of
  *  traversing fragment lists and such.
  */
 
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len)
 {
     int start = skb_headlen(skb);
     struct sk_buff *frag_iter;
     int i, copy;
 
     if (offset > (int)skb->len - len)
         goto fault;
 
     if ((copy = start - offset) > 0) {
         if (copy > len)
             copy = len;
         skb_copy_to_linear_data_offset(skb, offset, from, copy);
         if ((len -= copy) == 0)
             return 0;
         offset += copy;
         from += copy;
     }
 
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + skb_frag_size(frag);
         if ((copy = end - offset) > 0) {
             u32 p_off, p_len, copied;
             struct page *p;
             u8 *vaddr;
 
             if (copy > len)
                 copy = len;
 
             skb_frag_foreach_page(frag,
                           skb_frag_off(frag) + offset - start,
                           copy, p, p_off, p_len, copied) {
                 vaddr = kmap_atomic(p);
                 memcpy(vaddr + p_off, from + copied, p_len);
                 kunmap_atomic(vaddr);
             }
 
             if ((len -= copy) == 0)
                 return 0;
             offset += copy;
             from += copy;
         }
         start = end;
     }
 
     skb_walk_frags(skb, frag_iter) {
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + frag_iter->len;
         if ((copy = end - offset) > 0) {
             if (copy > len)
                 copy = len;
             if (skb_store_bits(frag_iter, offset - start,
                        from, copy))
                 goto fault;
             if ((len -= copy) == 0)
                 return 0;
             offset += copy;
             from += copy;
         }
         start = end;
     }
     if (!len)
         return 0;
 
 fault:
     return -EFAULT;
 }
 EXPORT_SYMBOL(skb_store_bits);
 
 /* Checksum skb data. */
 __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
               __wsum csum, const struct skb_checksum_ops *ops)
 {
     int start = skb_headlen(skb);
     int i, copy = start - offset;
     struct sk_buff *frag_iter;
     int pos = 0;
 
     /* Checksum header. */
     if (copy > 0) {
         if (copy > len)
             copy = len;
         csum = INDIRECT_CALL_1(ops->update, csum_partial_ext,
                        skb->data + offset, copy, csum);
         if ((len -= copy) == 0)
             return csum;
         offset += copy;
         pos = copy;
     }
 
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int end;
         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
         WARN_ON(start > offset + len);
 
         end = start + skb_frag_size(frag);
         if ((copy = end - offset) > 0) {
             u32 p_off, p_len, copied;
             struct page *p;
             __wsum csum2;
             u8 *vaddr;
 
             if (copy > len)
                 copy = len;
 
             skb_frag_foreach_page(frag,
                           skb_frag_off(frag) + offset - start,
                           copy, p, p_off, p_len, copied) {
                 vaddr = kmap_atomic(p);
                 csum2 = INDIRECT_CALL_1(ops->update,
                             csum_partial_ext,
                             vaddr + p_off, p_len, 0);
                 kunmap_atomic(vaddr);
                 csum = INDIRECT_CALL_1(ops->combine,
                                csum_block_add_ext, csum,
                                csum2, pos, p_len);
                 pos += p_len;
             }
 
             if (!(len -= copy))
                 return csum;
             offset += copy;
         }
         start = end;
     }
 
     skb_walk_frags(skb, frag_iter) {
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + frag_iter->len;
         if ((copy = end - offset) > 0) {
             __wsum csum2;
             if (copy > len)
                 copy = len;
             csum2 = __skb_checksum(frag_iter, offset - start,
                            copy, 0, ops);
             csum = INDIRECT_CALL_1(ops->combine, csum_block_add_ext,
                            csum, csum2, pos, copy);
             if ((len -= copy) == 0)
                 return csum;
             offset += copy;
             pos    += copy;
         }
         start = end;
     }
     BUG_ON(len);
 
     return csum;
 }
 EXPORT_SYMBOL(__skb_checksum);
 
 __wsum skb_checksum(const struct sk_buff *skb, int offset,
             int len, __wsum csum)
 {
     const struct skb_checksum_ops ops = {
         .update  = csum_partial_ext,
         .combine = csum_block_add_ext,
     };
 
     return __skb_checksum(skb, offset, len, csum, &ops);
 }
 EXPORT_SYMBOL(skb_checksum);
 
 /* Both of above in one bottle. */
 
 __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset,
                     u8 *to, int len)
 {
     int start = skb_headlen(skb);
     int i, copy = start - offset;
     struct sk_buff *frag_iter;
     int pos = 0;
     __wsum csum = 0;
 
     /* Copy header. */
     if (copy > 0) {
         if (copy > len)
             copy = len;
         csum = csum_partial_copy_nocheck(skb->data + offset, to,
                          copy);
         if ((len -= copy) == 0)
             return csum;
         offset += copy;
         to     += copy;
         pos = copy;
     }
 
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
         if ((copy = end - offset) > 0) {
             skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
             u32 p_off, p_len, copied;
             struct page *p;
             __wsum csum2;
             u8 *vaddr;
 
             if (copy > len)
                 copy = len;
 
             skb_frag_foreach_page(frag,
                           skb_frag_off(frag) + offset - start,
                           copy, p, p_off, p_len, copied) {
                 vaddr = kmap_atomic(p);
                 csum2 = csum_partial_copy_nocheck(vaddr + p_off,
                                   to + copied,
                                   p_len);
                 kunmap_atomic(vaddr);
                 csum = csum_block_add(csum, csum2, pos);
                 pos += p_len;
             }
 
             if (!(len -= copy))
                 return csum;
             offset += copy;
             to     += copy;
         }
         start = end;
     }
 
     skb_walk_frags(skb, frag_iter) {
         __wsum csum2;
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + frag_iter->len;
         if ((copy = end - offset) > 0) {
             if (copy > len)
                 copy = len;
             csum2 = skb_copy_and_csum_bits(frag_iter,
                                offset - start,
                                to, copy);
             csum = csum_block_add(csum, csum2, pos);
             if ((len -= copy) == 0)
                 return csum;
             offset += copy;
             to     += copy;
             pos    += copy;
         }
         start = end;
     }
     BUG_ON(len);
     return csum;
 }
 EXPORT_SYMBOL(skb_copy_and_csum_bits);
 
 __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
 {
     __sum16 sum;
 
     sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
     /* See comments in __skb_checksum_complete(). */
     if (likely(!sum)) {
         if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
             !skb->csum_complete_sw)
             netdev_rx_csum_fault(skb->dev, skb);
     }
     if (!skb_shared(skb))
         skb->csum_valid = !sum;
     return sum;
 }
 EXPORT_SYMBOL(__skb_checksum_complete_head);
 
 /* This function assumes skb->csum already holds pseudo header's checksum,
  * which has been changed from the hardware checksum, for example, by
  * __skb_checksum_validate_complete(). And, the original skb->csum must
  * have been validated unsuccessfully for CHECKSUM_COMPLETE case.
  *
  * It returns non-zero if the recomputed checksum is still invalid, otherwise
  * zero. The new checksum is stored back into skb->csum unless the skb is
  * shared.
  */
 __sum16 __skb_checksum_complete(struct sk_buff *skb)
 {
     __wsum csum;
     __sum16 sum;
 
     csum = skb_checksum(skb, 0, skb->len, 0);
 
     sum = csum_fold(csum_add(skb->csum, csum));
     /* This check is inverted, because we already knew the hardware
      * checksum is invalid before calling this function. So, if the
      * re-computed checksum is valid instead, then we have a mismatch
      * between the original skb->csum and skb_checksum(). This means either
      * the original hardware checksum is incorrect or we screw up skb->csum
      * when moving skb->data around.
      */
     if (likely(!sum)) {
         if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
             !skb->csum_complete_sw)
             netdev_rx_csum_fault(skb->dev, skb);
     }
 
     if (!skb_shared(skb)) {
         /* Save full packet checksum */
         skb->csum = csum;
         skb->ip_summed = CHECKSUM_COMPLETE;
         skb->csum_complete_sw = 1;
         skb->csum_valid = !sum;
     }
 
     return sum;
 }
 EXPORT_SYMBOL(__skb_checksum_complete);
 
 static __wsum warn_crc32c_csum_update(const void *buff, int len, __wsum sum)
 {
     net_warn_ratelimited(
         "%s: attempt to compute crc32c without libcrc32c.ko\n",
         __func__);
     return 0;
 }
 
 static __wsum warn_crc32c_csum_combine(__wsum csum, __wsum csum2,
                        int offset, int len)
 {
     net_warn_ratelimited(
         "%s: attempt to compute crc32c without libcrc32c.ko\n",
         __func__);
     return 0;
 }
 
 static const struct skb_checksum_ops default_crc32c_ops = {
     .update  = warn_crc32c_csum_update,
     .combine = warn_crc32c_csum_combine,
 };
 
 const struct skb_checksum_ops *crc32c_csum_stub __read_mostly =
     &default_crc32c_ops;
 EXPORT_SYMBOL(crc32c_csum_stub);
 
  /**
  *  skb_zerocopy_headlen - Calculate headroom needed for skb_zerocopy()
  *  @from: source buffer
  *
  *  Calculates the amount of linear headroom needed in the 'to' skb passed
  *  into skb_zerocopy().
  */
 unsigned int
 skb_zerocopy_headlen(const struct sk_buff *from)
 {
     unsigned int hlen = 0;
 
     if (!from->head_frag ||
         skb_headlen(from) < L1_CACHE_BYTES ||
         skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS) {
         hlen = skb_headlen(from);
         if (!hlen)
             hlen = from->len;
     }
 
     if (skb_has_frag_list(from))
         hlen = from->len;
 
     return hlen;
 }
 EXPORT_SYMBOL_GPL(skb_zerocopy_headlen);
 
 /**
  *  skb_zerocopy - Zero copy skb to skb
  *  @to: destination buffer
  *  @from: source buffer
  *  @len: number of bytes to copy from source buffer
  *  @hlen: size of linear headroom in destination buffer
  *
  *  Copies up to `len` bytes from `from` to `to` by creating references
  *  to the frags in the source buffer.
  *
  *  The `hlen` as calculated by skb_zerocopy_headlen() specifies the
  *  headroom in the `to` buffer.
  *
  *  Return value:
  *  0: everything is OK
  *  -ENOMEM: couldn't orphan frags of @from due to lack of memory
  *  -EFAULT: skb_copy_bits() found some problem with skb geometry
  */
 int
 skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
 {
     int i, j = 0;
     int plen = 0; /* length of skb->head fragment */
     int ret;
     struct page *page;
     unsigned int offset;
 
     BUG_ON(!from->head_frag && !hlen);
 
     /* dont bother with small payloads */
     if (len <= skb_tailroom(to))
         return skb_copy_bits(from, 0, skb_put(to, len), len);
 
     if (hlen) {
         ret = skb_copy_bits(from, 0, skb_put(to, hlen), hlen);
         if (unlikely(ret))
             return ret;
         len -= hlen;
     } else {
         plen = min_t(int, skb_headlen(from), len);
         if (plen) {
             page = virt_to_head_page(from->head);
             offset = from->data - (unsigned char *)page_address(page);
             __skb_fill_page_desc(to, 0, page, offset, plen);
             get_page(page);
             j = 1;
             len -= plen;
         }
     }
 
     skb_len_add(to, len + plen);
 
     if (unlikely(skb_orphan_frags(from, GFP_ATOMIC))) {
         skb_tx_error(from);
         return -ENOMEM;
     }
     skb_zerocopy_clone(to, from, GFP_ATOMIC);
 
     for (i = 0; i < skb_shinfo(from)->nr_frags; i++) {
         int size;
 
         if (!len)
             break;
         skb_shinfo(to)->frags[j] = skb_shinfo(from)->frags[i];
         size = min_t(int, skb_frag_size(&skb_shinfo(to)->frags[j]),
                     len);
         skb_frag_size_set(&skb_shinfo(to)->frags[j], size);
         len -= size;
         skb_frag_ref(to, j);
         j++;
     }
     skb_shinfo(to)->nr_frags = j;
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_zerocopy);
 
 void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to)
 {
     __wsum csum;
     long csstart;
 
     if (skb->ip_summed == CHECKSUM_PARTIAL)
         csstart = skb_checksum_start_offset(skb);
     else
         csstart = skb_headlen(skb);
 
     BUG_ON(csstart > skb_headlen(skb));
 
     skb_copy_from_linear_data(skb, to, csstart);
 
     csum = 0;
     if (csstart != skb->len)
         csum = skb_copy_and_csum_bits(skb, csstart, to + csstart,
                           skb->len - csstart);
 
     if (skb->ip_summed == CHECKSUM_PARTIAL) {
         long csstuff = csstart + skb->csum_offset;
 
         *((__sum16 *)(to + csstuff)) = csum_fold(csum);
     }
 }
 EXPORT_SYMBOL(skb_copy_and_csum_dev);
 
 /**
  *  skb_dequeue - remove from the head of the queue
  *  @list: list to dequeue from
  *
  *  Remove the head of the list. The list lock is taken so the function
  *  may be used safely with other locking list functions. The head item is
  *  returned or %NULL if the list is empty.
  */
 
 struct sk_buff *skb_dequeue(struct sk_buff_head *list)
 {
     unsigned long flags;
     struct sk_buff *result;
 
     spin_lock_irqsave(&list->lock, flags);
     result = __skb_dequeue(list);
     spin_unlock_irqrestore(&list->lock, flags);
     return result;
 }
 EXPORT_SYMBOL(skb_dequeue);
 
 /**
  *  skb_dequeue_tail - remove from the tail of the queue
  *  @list: list to dequeue from
  *
  *  Remove the tail of the list. The list lock is taken so the function
  *  may be used safely with other locking list functions. The tail item is
  *  returned or %NULL if the list is empty.
  */
 struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list)
 {
     unsigned long flags;
     struct sk_buff *result;
 
     spin_lock_irqsave(&list->lock, flags);
     result = __skb_dequeue_tail(list);
     spin_unlock_irqrestore(&list->lock, flags);
     return result;
 }
 EXPORT_SYMBOL(skb_dequeue_tail);
 
 /**
  *  skb_queue_purge - empty a list
  *  @list: list to empty
  *
  *  Delete all buffers on an &sk_buff list. Each buffer is removed from
  *  the list and one reference dropped. This function takes the list
  *  lock and is atomic with respect to other list locking functions.
  */
 void skb_queue_purge(struct sk_buff_head *list)
 {
     struct sk_buff *skb;
     while ((skb = skb_dequeue(list)) != NULL)
         kfree_skb(skb);
 }
 EXPORT_SYMBOL(skb_queue_purge);
 
 /**
  *  skb_rbtree_purge - empty a skb rbtree
  *  @root: root of the rbtree to empty
  *  Return value: the sum of truesizes of all purged skbs.
  *
  *  Delete all buffers on an &sk_buff rbtree. Each buffer is removed from
  *  the list and one reference dropped. This function does not take
  *  any lock. Synchronization should be handled by the caller (e.g., TCP
  *  out-of-order queue is protected by the socket lock).
  */
 unsigned int skb_rbtree_purge(struct rb_root *root)
 {
     struct rb_node *p = rb_first(root);
     unsigned int sum = 0;
 
     while (p) {
         struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
 
         p = rb_next(p);
         rb_erase(&skb->rbnode, root);
         sum += skb->truesize;
         kfree_skb(skb);
     }
     return sum;
 }
 
 /**
  *  skb_queue_head - queue a buffer at the list head
  *  @list: list to use
  *  @newsk: buffer to queue
  *
  *  Queue a buffer at the start of the list. This function takes the
  *  list lock and can be used safely with other locking &sk_buff functions
  *  safely.
  *
  *  A buffer cannot be placed on two lists at the same time.
  */
 void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&list->lock, flags);
     __skb_queue_head(list, newsk);
     spin_unlock_irqrestore(&list->lock, flags);
 }
 EXPORT_SYMBOL(skb_queue_head);
 
 /**
  *  skb_queue_tail - queue a buffer at the list tail
  *  @list: list to use
  *  @newsk: buffer to queue
  *
  *  Queue a buffer at the tail of the list. This function takes the
  *  list lock and can be used safely with other locking &sk_buff functions
  *  safely.
  *
  *  A buffer cannot be placed on two lists at the same time.
  */
 void skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&list->lock, flags);
     __skb_queue_tail(list, newsk);
     spin_unlock_irqrestore(&list->lock, flags);
 }
 EXPORT_SYMBOL(skb_queue_tail);
 
 /**
  *  skb_unlink  -   remove a buffer from a list
  *  @skb: buffer to remove
  *  @list: list to use
  *
  *  Remove a packet from a list. The list locks are taken and this
  *  function is atomic with respect to other list locked calls
  *
  *  You must know what list the SKB is on.
  */
 void skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&list->lock, flags);
     __skb_unlink(skb, list);
     spin_unlock_irqrestore(&list->lock, flags);
 }
 EXPORT_SYMBOL(skb_unlink);
 
 /**
  *  skb_append  -   append a buffer
  *  @old: buffer to insert after
  *  @newsk: buffer to insert
  *  @list: list to use
  *
  *  Place a packet after a given packet in a list. The list locks are taken
  *  and this function is atomic with respect to other list locked calls.
  *  A buffer cannot be placed on two lists at the same time.
  */
 void skb_append(struct sk_buff *old, struct sk_buff *newsk, struct sk_buff_head *list)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&list->lock, flags);
     __skb_queue_after(list, old, newsk);
     spin_unlock_irqrestore(&list->lock, flags);
 }
 EXPORT_SYMBOL(skb_append);
 
 static inline void skb_split_inside_header(struct sk_buff *skb,
                        struct sk_buff* skb1,
                        const u32 len, const int pos)
 {
     int i;
 
     skb_copy_from_linear_data_offset(skb, len, skb_put(skb1, pos - len),
                      pos - len);
     /* And move data appendix as is. */
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
         skb_shinfo(skb1)->frags[i] = skb_shinfo(skb)->frags[i];
 
     skb_shinfo(skb1)->nr_frags = skb_shinfo(skb)->nr_frags;
     skb_shinfo(skb)->nr_frags  = 0;
     skb1->data_len         = skb->data_len;
     skb1->len          += skb1->data_len;
     skb->data_len          = 0;
     skb->len           = len;
     skb_set_tail_pointer(skb, len);
 }
 
 static inline void skb_split_no_header(struct sk_buff *skb,
                        struct sk_buff* skb1,
                        const u32 len, int pos)
 {
     int i, k = 0;
     const int nfrags = skb_shinfo(skb)->nr_frags;
 
     skb_shinfo(skb)->nr_frags = 0;
     skb1->len         = skb1->data_len = skb->len - len;
     skb->len          = len;
     skb->data_len         = len - pos;
 
     for (i = 0; i < nfrags; i++) {
         int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 
         if (pos + size > len) {
             skb_shinfo(skb1)->frags[k] = skb_shinfo(skb)->frags[i];
 
             if (pos < len) {
                 /* Split frag.
                  * We have two variants in this case:
                  * 1. Move all the frag to the second
                  *    part, if it is possible. F.e.
                  *    this approach is mandatory for TUX,
                  *    where splitting is expensive.
                  * 2. Split is accurately. We make this.
                  */
                 skb_frag_ref(skb, i);
                 skb_frag_off_add(&skb_shinfo(skb1)->frags[0], len - pos);
                 skb_frag_size_sub(&skb_shinfo(skb1)->frags[0], len - pos);
                 skb_frag_size_set(&skb_shinfo(skb)->frags[i], len - pos);
                 skb_shinfo(skb)->nr_frags++;
             }
             k++;
         } else
             skb_shinfo(skb)->nr_frags++;
         pos += size;
     }
     skb_shinfo(skb1)->nr_frags = k;
 }
 
 /**
  * skb_split - Split fragmented skb to two parts at length len.
  * @skb: the buffer to split
  * @skb1: the buffer to receive the second part
  * @len: new length for skb
  */
 void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
 {
     int pos = skb_headlen(skb);
     const int zc_flags = SKBFL_SHARED_FRAG | SKBFL_PURE_ZEROCOPY;
 
     skb_zcopy_downgrade_managed(skb);
 
     skb_shinfo(skb1)->flags |= skb_shinfo(skb)->flags & zc_flags;
     skb_zerocopy_clone(skb1, skb, 0);
     if (len < pos)  /* Split line is inside header. */
         skb_split_inside_header(skb, skb1, len, pos);
     else        /* Second chunk has no header, nothing to copy. */
         skb_split_no_header(skb, skb1, len, pos);
 }
 EXPORT_SYMBOL(skb_split);
 
 /* Shifting from/to a cloned skb is a no-go.
  *
  * Caller cannot keep skb_shinfo related pointers past calling here!
  */
 static int skb_prepare_for_shift(struct sk_buff *skb)
 {
     return skb_unclone_keeptruesize(skb, GFP_ATOMIC);
 }
 
 /**
  * skb_shift - Shifts paged data partially from skb to another
  * @tgt: buffer into which tail data gets added
  * @skb: buffer from which the paged data comes from
  * @shiftlen: shift up to this many bytes
  *
  * Attempts to shift up to shiftlen worth of bytes, which may be less than
  * the length of the skb, from skb to tgt. Returns number bytes shifted.
  * It's up to caller to free skb if everything was shifted.
  *
  * If @tgt runs out of frags, the whole operation is aborted.
  *
  * Skb cannot include anything else but paged data while tgt is allowed
  * to have non-paged data as well.
  *
  * TODO: full sized shift could be optimized but that would need
  * specialized skb free'er to handle frags without up-to-date nr_frags.
  */
 int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
 {
     int from, to, merge, todo;
     skb_frag_t *fragfrom, *fragto;
 
     BUG_ON(shiftlen > skb->len);
 
     if (skb_headlen(skb))
         return 0;
     if (skb_zcopy(tgt) || skb_zcopy(skb))
         return 0;
 
     todo = shiftlen;
     from = 0;
     to = skb_shinfo(tgt)->nr_frags;
     fragfrom = &skb_shinfo(skb)->frags[from];
 
     /* Actual merge is delayed until the point when we know we can
      * commit all, so that we don't have to undo partial changes
      */
     if (!to ||
         !skb_can_coalesce(tgt, to, skb_frag_page(fragfrom),
                   skb_frag_off(fragfrom))) {
         merge = -1;
     } else {
         merge = to - 1;
 
         todo -= skb_frag_size(fragfrom);
         if (todo < 0) {
             if (skb_prepare_for_shift(skb) ||
                 skb_prepare_for_shift(tgt))
                 return 0;
 
             /* All previous frag pointers might be stale! */
             fragfrom = &skb_shinfo(skb)->frags[from];
             fragto = &skb_shinfo(tgt)->frags[merge];
 
             skb_frag_size_add(fragto, shiftlen);
             skb_frag_size_sub(fragfrom, shiftlen);
             skb_frag_off_add(fragfrom, shiftlen);
 
             goto onlymerged;
         }
 
         from++;
     }
 
     /* Skip full, not-fitting skb to avoid expensive operations */
     if ((shiftlen == skb->len) &&
         (skb_shinfo(skb)->nr_frags - from) > (MAX_SKB_FRAGS - to))
         return 0;
 
     if (skb_prepare_for_shift(skb) || skb_prepare_for_shift(tgt))
         return 0;
 
     while ((todo > 0) && (from < skb_shinfo(skb)->nr_frags)) {
         if (to == MAX_SKB_FRAGS)
             return 0;
 
         fragfrom = &skb_shinfo(skb)->frags[from];
         fragto = &skb_shinfo(tgt)->frags[to];
 
         if (todo >= skb_frag_size(fragfrom)) {
             *fragto = *fragfrom;
             todo -= skb_frag_size(fragfrom);
             from++;
             to++;
 
         } else {
             __skb_frag_ref(fragfrom);
             skb_frag_page_copy(fragto, fragfrom);
             skb_frag_off_copy(fragto, fragfrom);
             skb_frag_size_set(fragto, todo);
 
             skb_frag_off_add(fragfrom, todo);
             skb_frag_size_sub(fragfrom, todo);
             todo = 0;
 
             to++;
             break;
         }
     }
 
     /* Ready to "commit" this state change to tgt */
     skb_shinfo(tgt)->nr_frags = to;
 
     if (merge >= 0) {
         fragfrom = &skb_shinfo(skb)->frags[0];
         fragto = &skb_shinfo(tgt)->frags[merge];
 
         skb_frag_size_add(fragto, skb_frag_size(fragfrom));
         __skb_frag_unref(fragfrom, skb->pp_recycle);
     }
 
     /* Reposition in the original skb */
     to = 0;
     while (from < skb_shinfo(skb)->nr_frags)
         skb_shinfo(skb)->frags[to++] = skb_shinfo(skb)->frags[from++];
     skb_shinfo(skb)->nr_frags = to;
 
     BUG_ON(todo > 0 && !skb_shinfo(skb)->nr_frags);
 
 onlymerged:
     /* Most likely the tgt won't ever need its checksum anymore, skb on
      * the other hand might need it if it needs to be resent
      */
     tgt->ip_summed = CHECKSUM_PARTIAL;
     skb->ip_summed = CHECKSUM_PARTIAL;
 
     skb_len_add(skb, -shiftlen);
     skb_len_add(tgt, shiftlen);
 
     return shiftlen;
 }
 
 /**
  * skb_prepare_seq_read - Prepare a sequential read of skb data
  * @skb: the buffer to read
  * @from: lower offset of data to be read
  * @to: upper offset of data to be read
  * @st: state variable
  *
  * Initializes the specified state variable. Must be called before
  * invoking skb_seq_read() for the first time.
  */
 void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
               unsigned int to, struct skb_seq_state *st)
 {
     st->lower_offset = from;
     st->upper_offset = to;
     st->root_skb = st->cur_skb = skb;
     st->frag_idx = st->stepped_offset = 0;
     st->frag_data = NULL;
     st->frag_off = 0;
 }
 EXPORT_SYMBOL(skb_prepare_seq_read);
 
 /**
  * skb_seq_read - Sequentially read skb data
  * @consumed: number of bytes consumed by the caller so far
  * @data: destination pointer for data to be returned
  * @st: state variable
  *
  * Reads a block of skb data at @consumed relative to the
  * lower offset specified to skb_prepare_seq_read(). Assigns
  * the head of the data block to @data and returns the length
  * of the block or 0 if the end of the skb data or the upper
  * offset has been reached.
  *
  * The caller is not required to consume all of the data
  * returned, i.e. @consumed is typically set to the number
  * of bytes already consumed and the next call to
  * skb_seq_read() will return the remaining part of the block.
  *
  * Note 1: The size of each block of data returned can be arbitrary,
  *       this limitation is the cost for zerocopy sequential
  *       reads of potentially non linear data.
  *
  * Note 2: Fragment lists within fragments are not implemented
  *       at the moment, state->root_skb could be replaced with
  *       a stack for this purpose.
  */
 unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
               struct skb_seq_state *st)
 {
     unsigned int block_limit, abs_offset = consumed + st->lower_offset;
     skb_frag_t *frag;
 
     if (unlikely(abs_offset >= st->upper_offset)) {
         if (st->frag_data) {
             kunmap_atomic(st->frag_data);
             st->frag_data = NULL;
         }
         return 0;
     }
 
 next_skb:
     block_limit = skb_headlen(st->cur_skb) + st->stepped_offset;
 
     if (abs_offset < block_limit && !st->frag_data) {
         *data = st->cur_skb->data + (abs_offset - st->stepped_offset);
         return block_limit - abs_offset;
     }
 
     if (st->frag_idx == 0 && !st->frag_data)
         st->stepped_offset += skb_headlen(st->cur_skb);
 
     while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags) {
         unsigned int pg_idx, pg_off, pg_sz;
 
         frag = &skb_shinfo(st->cur_skb)->frags[st->frag_idx];
 
         pg_idx = 0;
         pg_off = skb_frag_off(frag);
         pg_sz = skb_frag_size(frag);
 
         if (skb_frag_must_loop(skb_frag_page(frag))) {
             pg_idx = (pg_off + st->frag_off) >> PAGE_SHIFT;
             pg_off = offset_in_page(pg_off + st->frag_off);
             pg_sz = min_t(unsigned int, pg_sz - st->frag_off,
                             PAGE_SIZE - pg_off);
         }
 
         block_limit = pg_sz + st->stepped_offset;
         if (abs_offset < block_limit) {
             if (!st->frag_data)
                 st->frag_data = kmap_atomic(skb_frag_page(frag) + pg_idx);
 
             *data = (u8 *)st->frag_data + pg_off +
                 (abs_offset - st->stepped_offset);
 
             return block_limit - abs_offset;
         }
 
         if (st->frag_data) {
             kunmap_atomic(st->frag_data);
             st->frag_data = NULL;
         }
 
         st->stepped_offset += pg_sz;
         st->frag_off += pg_sz;
         if (st->frag_off == skb_frag_size(frag)) {
             st->frag_off = 0;
             st->frag_idx++;
         }
     }
 
     if (st->frag_data) {
         kunmap_atomic(st->frag_data);
         st->frag_data = NULL;
     }
 
     if (st->root_skb == st->cur_skb && skb_has_frag_list(st->root_skb)) {
         st->cur_skb = skb_shinfo(st->root_skb)->frag_list;
         st->frag_idx = 0;
         goto next_skb;
     } else if (st->cur_skb->next) {
         st->cur_skb = st->cur_skb->next;
         st->frag_idx = 0;
         goto next_skb;
     }
 
     return 0;
 }
 EXPORT_SYMBOL(skb_seq_read);
 
 /**
  * skb_abort_seq_read - Abort a sequential read of skb data
  * @st: state variable
  *
  * Must be called if skb_seq_read() was not called until it
  * returned 0.
  */
 void skb_abort_seq_read(struct skb_seq_state *st)
 {
     if (st->frag_data)
         kunmap_atomic(st->frag_data);
 }
 EXPORT_SYMBOL(skb_abort_seq_read);
 
 #define TS_SKB_CB(state)    ((struct skb_seq_state *) &((state)->cb))
 
 static unsigned int skb_ts_get_next_block(unsigned int offset, const u8 **text,
                       struct ts_config *conf,
                       struct ts_state *state)
 {
     return skb_seq_read(offset, text, TS_SKB_CB(state));
 }
 
 static void skb_ts_finish(struct ts_config *conf, struct ts_state *state)
 {
     skb_abort_seq_read(TS_SKB_CB(state));
 }
 
 /**
  * skb_find_text - Find a text pattern in skb data
  * @skb: the buffer to look in
  * @from: search offset
  * @to: search limit
  * @config: textsearch configuration
  *
  * Finds a pattern in the skb data according to the specified
  * textsearch configuration. Use textsearch_next() to retrieve
  * subsequent occurrences of the pattern. Returns the offset
  * to the first occurrence or UINT_MAX if no match was found.
  */
 unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
                unsigned int to, struct ts_config *config)
 {
     struct ts_state state;
     unsigned int ret;
 
     BUILD_BUG_ON(sizeof(struct skb_seq_state) > sizeof(state.cb));
 
     config->get_next_block = skb_ts_get_next_block;
     config->finish = skb_ts_finish;
 
     skb_prepare_seq_read(skb, from, to, TS_SKB_CB(&state));
 
     ret = textsearch_find(config, &state);
     return (ret <= to - from ? ret : UINT_MAX);
 }
 EXPORT_SYMBOL(skb_find_text);
 
 int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
              int offset, size_t size)
 {
     int i = skb_shinfo(skb)->nr_frags;
 
     if (skb_can_coalesce(skb, i, page, offset)) {
         skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
     } else if (i < MAX_SKB_FRAGS) {
         skb_zcopy_downgrade_managed(skb);
         get_page(page);
         skb_fill_page_desc(skb, i, page, offset, size);
     } else {
         return -EMSGSIZE;
     }
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_append_pagefrags);
 
 /**
  *  skb_pull_rcsum - pull skb and update receive checksum
  *  @skb: buffer to update
  *  @len: length of data pulled
  *
  *  This function performs an skb_pull on the packet and updates
  *  the CHECKSUM_COMPLETE checksum.  It should be used on
  *  receive path processing instead of skb_pull unless you know
  *  that the checksum difference is zero (e.g., a valid IP header)
  *  or you are setting ip_summed to CHECKSUM_NONE.
  */
 void *skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
 {
     unsigned char *data = skb->data;
 
     BUG_ON(len > skb->len);
     __skb_pull(skb, len);
     skb_postpull_rcsum(skb, data, len);
     return skb->data;
 }
 EXPORT_SYMBOL_GPL(skb_pull_rcsum);
 
 static inline skb_frag_t skb_head_frag_to_page_desc(struct sk_buff *frag_skb)
 {
     skb_frag_t head_frag;
     struct page *page;
 
     page = virt_to_head_page(frag_skb->head);
     __skb_frag_set_page(&head_frag, page);
     skb_frag_off_set(&head_frag, frag_skb->data -
              (unsigned char *)page_address(page));
     skb_frag_size_set(&head_frag, skb_headlen(frag_skb));
     return head_frag;
 }
 
 struct sk_buff *skb_segment_list(struct sk_buff *skb,
                  netdev_features_t features,
                  unsigned int offset)
 {
     struct sk_buff *list_skb = skb_shinfo(skb)->frag_list;
     unsigned int tnl_hlen = skb_tnl_header_len(skb);
     unsigned int delta_truesize = 0;
     unsigned int delta_len = 0;
     struct sk_buff *tail = NULL;
     struct sk_buff *nskb, *tmp;
     int len_diff, err;
 
     skb_push(skb, -skb_network_offset(skb) + offset);
 
     skb_shinfo(skb)->frag_list = NULL;
 
     do {
         nskb = list_skb;
         list_skb = list_skb->next;
 
         err = 0;
         delta_truesize += nskb->truesize;
         if (skb_shared(nskb)) {
             tmp = skb_clone(nskb, GFP_ATOMIC);
             if (tmp) {
                 consume_skb(nskb);
                 nskb = tmp;
                 err = skb_unclone(nskb, GFP_ATOMIC);
             } else {
                 err = -ENOMEM;
             }
         }
 
         if (!tail)
             skb->next = nskb;
         else
             tail->next = nskb;
 
         if (unlikely(err)) {
             nskb->next = list_skb;
             goto err_linearize;
         }
 
         tail = nskb;
 
         delta_len += nskb->len;
 
         skb_push(nskb, -skb_network_offset(nskb) + offset);
 
         skb_release_head_state(nskb);
         len_diff = skb_network_header_len(nskb) - skb_network_header_len(skb);
         __copy_skb_header(nskb, skb);
 
         skb_headers_offset_update(nskb, skb_headroom(nskb) - skb_headroom(skb));
         nskb->transport_header += len_diff;
         skb_copy_from_linear_data_offset(skb, -tnl_hlen,
                          nskb->data - tnl_hlen,
                          offset + tnl_hlen);
 
         if (skb_needs_linearize(nskb, features) &&
             __skb_linearize(nskb))
             goto err_linearize;
 
     } while (list_skb);
 
     skb->truesize = skb->truesize - delta_truesize;
     skb->data_len = skb->data_len - delta_len;
     skb->len = skb->len - delta_len;
 
     skb_gso_reset(skb);
 
     skb->prev = tail;
 
     if (skb_needs_linearize(skb, features) &&
         __skb_linearize(skb))
         goto err_linearize;
 
     skb_get(skb);
 
     return skb;
 
 err_linearize:
     kfree_skb_list(skb->next);
     skb->next = NULL;
     return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL_GPL(skb_segment_list);
 
 /**
  *  skb_segment - Perform protocol segmentation on skb.
  *  @head_skb: buffer to segment
  *  @features: features for the output path (see dev->features)
  *
  *  This function performs segmentation on the given skb.  It returns
  *  a pointer to the first in a list of new skbs for the segments.
  *  In case of error it returns ERR_PTR(err).
  */
 struct sk_buff *skb_segment(struct sk_buff *head_skb,
                 netdev_features_t features)
 {
     struct sk_buff *segs = NULL;
     struct sk_buff *tail = NULL;
     struct sk_buff *list_skb = skb_shinfo(head_skb)->frag_list;
     skb_frag_t *frag = skb_shinfo(head_skb)->frags;
     unsigned int mss = skb_shinfo(head_skb)->gso_size;
     unsigned int doffset = head_skb->data - skb_mac_header(head_skb);
     struct sk_buff *frag_skb = head_skb;
     unsigned int offset = doffset;
     unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
     unsigned int partial_segs = 0;
     unsigned int headroom;
     unsigned int len = head_skb->len;
     __be16 proto;
     bool csum, sg;
     int nfrags = skb_shinfo(head_skb)->nr_frags;
     int err = -ENOMEM;
     int i = 0;
     int pos;
 
     if (list_skb && !list_skb->head_frag && skb_headlen(list_skb) &&
         (skb_shinfo(head_skb)->gso_type & SKB_GSO_DODGY)) {
         /* gso_size is untrusted, and we have a frag_list with a linear
          * non head_frag head.
          *
          * (we assume checking the first list_skb member suffices;
          * i.e if either of the list_skb members have non head_frag
          * head, then the first one has too).
          *
          * If head_skb's headlen does not fit requested gso_size, it
          * means that the frag_list members do NOT terminate on exact
          * gso_size boundaries. Hence we cannot perform skb_frag_t page
          * sharing. Therefore we must fallback to copying the frag_list
          * skbs; we do so by disabling SG.
          */
         if (mss != GSO_BY_FRAGS && mss != skb_headlen(head_skb))
             features &= ~NETIF_F_SG;
     }
 
     __skb_push(head_skb, doffset);
     proto = skb_network_protocol(head_skb, NULL);
     if (unlikely(!proto))
         return ERR_PTR(-EINVAL);
 
     sg = !!(features & NETIF_F_SG);
     csum = !!can_checksum_protocol(features, proto);
 
     if (sg && csum && (mss != GSO_BY_FRAGS))  {
         if (!(features & NETIF_F_GSO_PARTIAL)) {
             struct sk_buff *iter;
             unsigned int frag_len;
 
             if (!list_skb ||
                 !net_gso_ok(features, skb_shinfo(head_skb)->gso_type))
                 goto normal;
 
             /* If we get here then all the required
              * GSO features except frag_list are supported.
              * Try to split the SKB to multiple GSO SKBs
              * with no frag_list.
              * Currently we can do that only when the buffers don't
              * have a linear part and all the buffers except
              * the last are of the same length.
              */
             frag_len = list_skb->len;
             skb_walk_frags(head_skb, iter) {
                 if (frag_len != iter->len && iter->next)
                     goto normal;
                 if (skb_headlen(iter) && !iter->head_frag)
                     goto normal;
 
                 len -= iter->len;
             }
 
             if (len != frag_len)
                 goto normal;
         }
 
         /* GSO partial only requires that we trim off any excess that
          * doesn't fit into an MSS sized block, so take care of that
          * now.
          */
         partial_segs = len / mss;
         if (partial_segs > 1)
             mss *= partial_segs;
         else
             partial_segs = 0;
     }
 
 normal:
     headroom = skb_headroom(head_skb);
     pos = skb_headlen(head_skb);
 
     do {
         struct sk_buff *nskb;
         skb_frag_t *nskb_frag;
         int hsize;
         int size;
 
         if (unlikely(mss == GSO_BY_FRAGS)) {
             len = list_skb->len;
         } else {
             len = head_skb->len - offset;
             if (len > mss)
                 len = mss;
         }
 
         hsize = skb_headlen(head_skb) - offset;
 
         if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
             (skb_headlen(list_skb) == len || sg)) {
             BUG_ON(skb_headlen(list_skb) > len);
 
             i = 0;
             nfrags = skb_shinfo(list_skb)->nr_frags;
             frag = skb_shinfo(list_skb)->frags;
             frag_skb = list_skb;
             pos += skb_headlen(list_skb);
 
             while (pos < offset + len) {
                 BUG_ON(i >= nfrags);
 
                 size = skb_frag_size(frag);
                 if (pos + size > offset + len)
                     break;
 
                 i++;
                 pos += size;
                 frag++;
             }
 
             nskb = skb_clone(list_skb, GFP_ATOMIC);
             list_skb = list_skb->next;
 
             if (unlikely(!nskb))
                 goto err;
 
             if (unlikely(pskb_trim(nskb, len))) {
                 kfree_skb(nskb);
                 goto err;
             }
 
             hsize = skb_end_offset(nskb);
             if (skb_cow_head(nskb, doffset + headroom)) {
                 kfree_skb(nskb);
                 goto err;
             }
 
             nskb->truesize += skb_end_offset(nskb) - hsize;
             skb_release_head_state(nskb);
             __skb_push(nskb, doffset);
         } else {
             if (hsize < 0)
                 hsize = 0;
             if (hsize > len || !sg)
                 hsize = len;
 
             nskb = __alloc_skb(hsize + doffset + headroom,
                        GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
                        NUMA_NO_NODE);
 
             if (unlikely(!nskb))
                 goto err;
 
             skb_reserve(nskb, headroom);
             __skb_put(nskb, doffset);
         }
 
         if (segs)
             tail->next = nskb;
         else
             segs = nskb;
         tail = nskb;
 
         __copy_skb_header(nskb, head_skb);
 
         skb_headers_offset_update(nskb, skb_headroom(nskb) - headroom);
         skb_reset_mac_len(nskb);
 
         skb_copy_from_linear_data_offset(head_skb, -tnl_hlen,
                          nskb->data - tnl_hlen,
                          doffset + tnl_hlen);
 
         if (nskb->len == len + doffset)
             goto perform_csum_check;
 
         if (!sg) {
             if (!csum) {
                 if (!nskb->remcsum_offload)
                     nskb->ip_summed = CHECKSUM_NONE;
                 SKB_GSO_CB(nskb)->csum =
                     skb_copy_and_csum_bits(head_skb, offset,
                                    skb_put(nskb,
                                        len),
                                    len);
                 SKB_GSO_CB(nskb)->csum_start =
                     skb_headroom(nskb) + doffset;
             } else {
                 if (skb_copy_bits(head_skb, offset, skb_put(nskb, len), len))
                     goto err;
             }
             continue;
         }
 
         nskb_frag = skb_shinfo(nskb)->frags;
 
         skb_copy_from_linear_data_offset(head_skb, offset,
                          skb_put(nskb, hsize), hsize);
 
         skb_shinfo(nskb)->flags |= skb_shinfo(head_skb)->flags &
                        SKBFL_SHARED_FRAG;
 
         if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||
             skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC))
             goto err;
 
         while (pos < offset + len) {
             if (i >= nfrags) {
                 i = 0;
                 nfrags = skb_shinfo(list_skb)->nr_frags;
                 frag = skb_shinfo(list_skb)->frags;
                 frag_skb = list_skb;
                 if (!skb_headlen(list_skb)) {
                     BUG_ON(!nfrags);
                 } else {
                     BUG_ON(!list_skb->head_frag);
 
                     /* to make room for head_frag. */
                     i--;
                     frag--;
                 }
                 if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||
                     skb_zerocopy_clone(nskb, frag_skb,
                                GFP_ATOMIC))
                     goto err;
 
                 list_skb = list_skb->next;
             }
 
             if (unlikely(skb_shinfo(nskb)->nr_frags >=
                      MAX_SKB_FRAGS)) {
                 net_warn_ratelimited(
                     "skb_segment: too many frags: %u %u\n",
                     pos, mss);
                 err = -EINVAL;
                 goto err;
             }
 
             *nskb_frag = (i < 0) ? skb_head_frag_to_page_desc(frag_skb) : *frag;
             __skb_frag_ref(nskb_frag);
             size = skb_frag_size(nskb_frag);
 
             if (pos < offset) {
                 skb_frag_off_add(nskb_frag, offset - pos);
                 skb_frag_size_sub(nskb_frag, offset - pos);
             }
 
             skb_shinfo(nskb)->nr_frags++;
 
             if (pos + size <= offset + len) {
                 i++;
                 frag++;
                 pos += size;
             } else {
                 skb_frag_size_sub(nskb_frag, pos + size - (offset + len));
                 goto skip_fraglist;
             }
 
             nskb_frag++;
         }
 
 skip_fraglist:
         nskb->data_len = len - hsize;
         nskb->len += nskb->data_len;
         nskb->truesize += nskb->data_len;
 
 perform_csum_check:
         if (!csum) {
             if (skb_has_shared_frag(nskb) &&
                 __skb_linearize(nskb))
                 goto err;
 
             if (!nskb->remcsum_offload)
                 nskb->ip_summed = CHECKSUM_NONE;
             SKB_GSO_CB(nskb)->csum =
                 skb_checksum(nskb, doffset,
                          nskb->len - doffset, 0);
             SKB_GSO_CB(nskb)->csum_start =
                 skb_headroom(nskb) + doffset;
         }
     } while ((offset += len) < head_skb->len);
 
     /* Some callers want to get the end of the list.
      * Put it in segs->prev to avoid walking the list.
      * (see validate_xmit_skb_list() for example)
      */
     segs->prev = tail;
 
     if (partial_segs) {
         struct sk_buff *iter;
         int type = skb_shinfo(head_skb)->gso_type;
         unsigned short gso_size = skb_shinfo(head_skb)->gso_size;
 
         /* Update type to add partial and then remove dodgy if set */
         type |= (features & NETIF_F_GSO_PARTIAL) / NETIF_F_GSO_PARTIAL * SKB_GSO_PARTIAL;
         type &= ~SKB_GSO_DODGY;
 
         /* Update GSO info and prepare to start updating headers on
          * our way back down the stack of protocols.
          */
         for (iter = segs; iter; iter = iter->next) {
             skb_shinfo(iter)->gso_size = gso_size;
             skb_shinfo(iter)->gso_segs = partial_segs;
             skb_shinfo(iter)->gso_type = type;
             SKB_GSO_CB(iter)->data_offset = skb_headroom(iter) + doffset;
         }
 
         if (tail->len - doffset <= gso_size)
             skb_shinfo(tail)->gso_size = 0;
         else if (tail != segs)
             skb_shinfo(tail)->gso_segs = DIV_ROUND_UP(tail->len - doffset, gso_size);
     }
 
     /* Following permits correct backpressure, for protocols
      * using skb_set_owner_w().
      * Idea is to tranfert ownership from head_skb to last segment.
      */
     if (head_skb->destructor == sock_wfree) {
         swap(tail->truesize, head_skb->truesize);
         swap(tail->destructor, head_skb->destructor);
         swap(tail->sk, head_skb->sk);
     }
     return segs;
 
 err:
     kfree_skb_list(segs);
     return ERR_PTR(err);
 }
 EXPORT_SYMBOL_GPL(skb_segment);
 
 #ifdef CONFIG_SKB_EXTENSIONS
 #define SKB_EXT_ALIGN_VALUE 8
 #define SKB_EXT_CHUNKSIZEOF(x)  (ALIGN((sizeof(x)), SKB_EXT_ALIGN_VALUE) / SKB_EXT_ALIGN_VALUE)
 
 static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
     [SKB_EXT_BRIDGE_NF] = SKB_EXT_CHUNKSIZEOF(struct nf_bridge_info),
 #endif
 #ifdef CONFIG_XFRM
     [SKB_EXT_SEC_PATH] = SKB_EXT_CHUNKSIZEOF(struct sec_path),
 #endif
 #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
     [TC_SKB_EXT] = SKB_EXT_CHUNKSIZEOF(struct tc_skb_ext),
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
     [SKB_EXT_MPTCP] = SKB_EXT_CHUNKSIZEOF(struct mptcp_ext),
 #endif
 #if IS_ENABLED(CONFIG_MCTP_FLOWS)
     [SKB_EXT_MCTP] = SKB_EXT_CHUNKSIZEOF(struct mctp_flow),
 #endif
 };
 
 static __always_inline unsigned int skb_ext_total_length(void)
 {
     return SKB_EXT_CHUNKSIZEOF(struct skb_ext) +
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
         skb_ext_type_len[SKB_EXT_BRIDGE_NF] +
 #endif
 #ifdef CONFIG_XFRM
         skb_ext_type_len[SKB_EXT_SEC_PATH] +
 #endif
 #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
         skb_ext_type_len[TC_SKB_EXT] +
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
         skb_ext_type_len[SKB_EXT_MPTCP] +
 #endif
 #if IS_ENABLED(CONFIG_MCTP_FLOWS)
         skb_ext_type_len[SKB_EXT_MCTP] +
 #endif
         0;
 }
 
 static void skb_extensions_init(void)
 {
     BUILD_BUG_ON(SKB_EXT_NUM >= 8);
     BUILD_BUG_ON(skb_ext_total_length() > 255);
 
     skbuff_ext_cache = kmem_cache_create("skbuff_ext_cache",
                          SKB_EXT_ALIGN_VALUE * skb_ext_total_length(),
                          0,
                          SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                          NULL);
 }
 #else
 static void skb_extensions_init(void) {}
 #endif
 
 void __init skb_init(void)
 {
     skbuff_head_cache = kmem_cache_create_usercopy("skbuff_head_cache",
                           sizeof(struct sk_buff),
                           0,
                           SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                           offsetof(struct sk_buff, cb),
                           sizeof_field(struct sk_buff, cb),
                           NULL);
     skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
                         sizeof(struct sk_buff_fclones),
                         0,
                         SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                         NULL);
     skb_extensions_init();
 }
 
 static int
 __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len,
            unsigned int recursion_level)
 {
     int start = skb_headlen(skb);
     int i, copy = start - offset;
     struct sk_buff *frag_iter;
     int elt = 0;
 
     if (unlikely(recursion_level >= 24))
         return -EMSGSIZE;
 
     if (copy > 0) {
         if (copy > len)
             copy = len;
         sg_set_buf(sg, skb->data + offset, copy);
         elt++;
         if ((len -= copy) == 0)
             return elt;
         offset += copy;
     }
 
     for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
         int end;
 
         WARN_ON(start > offset + len);
 
         end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
         if ((copy = end - offset) > 0) {
             skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
             if (unlikely(elt && sg_is_last(&sg[elt - 1])))
                 return -EMSGSIZE;
 
             if (copy > len)
                 copy = len;
             sg_set_page(&sg[elt], skb_frag_page(frag), copy,
                     skb_frag_off(frag) + offset - start);
             elt++;
             if (!(len -= copy))
                 return elt;
             offset += copy;
         }
         start = end;
     }
 
     skb_walk_frags(skb, frag_iter) {
         int end, ret;
 
         WARN_ON(start > offset + len);
 
         end = start + frag_iter->len;
         if ((copy = end - offset) > 0) {
             if (unlikely(elt && sg_is_last(&sg[elt - 1])))
                 return -EMSGSIZE;
 
             if (copy > len)
                 copy = len;
             ret = __skb_to_sgvec(frag_iter, sg+elt, offset - start,
                           copy, recursion_level + 1);
             if (unlikely(ret < 0))
                 return ret;
             elt += ret;
             if ((len -= copy) == 0)
                 return elt;
             offset += copy;
         }
         start = end;
     }
     BUG_ON(len);
     return elt;
 }
 
 /**
  *  skb_to_sgvec - Fill a scatter-gather list from a socket buffer
  *  @skb: Socket buffer containing the buffers to be mapped
  *  @sg: The scatter-gather list to map into
  *  @offset: The offset into the buffer's contents to start mapping
  *  @len: Length of buffer space to be mapped
  *
  *  Fill the specified scatter-gather list with mappings/pointers into a
  *  region of the buffer space attached to a socket buffer. Returns either
  *  the number of scatterlist items used, or -EMSGSIZE if the contents
  *  could not fit.
  */
 int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
 {
     int nsg = __skb_to_sgvec(skb, sg, offset, len, 0);
 
     if (nsg <= 0)
         return nsg;
 
     sg_mark_end(&sg[nsg - 1]);
 
     return nsg;
 }
 EXPORT_SYMBOL_GPL(skb_to_sgvec);
 
 /* As compared with skb_to_sgvec, skb_to_sgvec_nomark only map skb to given
  * sglist without mark the sg which contain last skb data as the end.
  * So the caller can mannipulate sg list as will when padding new data after
  * the first call without calling sg_unmark_end to expend sg list.
  *
  * Scenario to use skb_to_sgvec_nomark:
  * 1. sg_init_table
  * 2. skb_to_sgvec_nomark(payload1)
  * 3. skb_to_sgvec_nomark(payload2)
  *
  * This is equivalent to:
  * 1. sg_init_table
  * 2. skb_to_sgvec(payload1)
  * 3. sg_unmark_end
  * 4. skb_to_sgvec(payload2)
  *
  * When mapping mutilple payload conditionally, skb_to_sgvec_nomark
  * is more preferable.
  */
 int skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
             int offset, int len)
 {
     return __skb_to_sgvec(skb, sg, offset, len, 0);
 }
 EXPORT_SYMBOL_GPL(skb_to_sgvec_nomark);
 
 
 
 /**
  *  skb_cow_data - Check that a socket buffer's data buffers are writable
  *  @skb: The socket buffer to check.
  *  @tailbits: Amount of trailing space to be added
  *  @trailer: Returned pointer to the skb where the @tailbits space begins
  *
  *  Make sure that the data buffers attached to a socket buffer are
  *  writable. If they are not, private copies are made of the data buffers
  *  and the socket buffer is set to use these instead.
  *
  *  If @tailbits is given, make sure that there is space to write @tailbits
  *  bytes of data beyond current end of socket buffer.  @trailer will be
  *  set to point to the skb in which this space begins.
  *
  *  The number of scatterlist elements required to completely map the
  *  COW'd and extended socket buffer will be returned.
  */
 int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer)
 {
     int copyflag;
     int elt;
     struct sk_buff *skb1, **skb_p;
 
     /* If skb is cloned or its head is paged, reallocate
      * head pulling out all the pages (pages are considered not writable
      * at the moment even if they are anonymous).
      */
     if ((skb_cloned(skb) || skb_shinfo(skb)->nr_frags) &&
         !__pskb_pull_tail(skb, __skb_pagelen(skb)))
         return -ENOMEM;
 
     /* Easy case. Most of packets will go this way. */
     if (!skb_has_frag_list(skb)) {
         /* A little of trouble, not enough of space for trailer.
          * This should not happen, when stack is tuned to generate
          * good frames. OK, on miss we reallocate and reserve even more
          * space, 128 bytes is fair. */
 
         if (skb_tailroom(skb) < tailbits &&
             pskb_expand_head(skb, 0, tailbits-skb_tailroom(skb)+128, GFP_ATOMIC))
             return -ENOMEM;
 
         /* Voila! */
         *trailer = skb;
         return 1;
     }
 
     /* Misery. We are in troubles, going to mincer fragments... */
 
     elt = 1;
     skb_p = &skb_shinfo(skb)->frag_list;
     copyflag = 0;
 
     while ((skb1 = *skb_p) != NULL) {
         int ntail = 0;
 
         /* The fragment is partially pulled by someone,
          * this can happen on input. Copy it and everything
          * after it. */
 
         if (skb_shared(skb1))
             copyflag = 1;
 
         /* If the skb is the last, worry about trailer. */
 
         if (skb1->next == NULL && tailbits) {
             if (skb_shinfo(skb1)->nr_frags ||
                 skb_has_frag_list(skb1) ||
                 skb_tailroom(skb1) < tailbits)
                 ntail = tailbits + 128;
         }
 
         if (copyflag ||
             skb_cloned(skb1) ||
             ntail ||
             skb_shinfo(skb1)->nr_frags ||
             skb_has_frag_list(skb1)) {
             struct sk_buff *skb2;
 
             /* Fuck, we are miserable poor guys... */
             if (ntail == 0)
                 skb2 = skb_copy(skb1, GFP_ATOMIC);
             else
                 skb2 = skb_copy_expand(skb1,
                                skb_headroom(skb1),
                                ntail,
                                GFP_ATOMIC);
             if (unlikely(skb2 == NULL))
                 return -ENOMEM;
 
             if (skb1->sk)
                 skb_set_owner_w(skb2, skb1->sk);
 
             /* Looking around. Are we still alive?
              * OK, link new skb, drop old one */
 
             skb2->next = skb1->next;
             *skb_p = skb2;
             kfree_skb(skb1);
             skb1 = skb2;
         }
         elt++;
         *trailer = skb1;
         skb_p = &skb1->next;
     }
 
     return elt;
 }
 EXPORT_SYMBOL_GPL(skb_cow_data);
 
 static void sock_rmem_free(struct sk_buff *skb)
 {
     struct sock *sk = skb->sk;
 
     atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
 }
 
 static void skb_set_err_queue(struct sk_buff *skb)
 {
     /* pkt_type of skbs received on local sockets is never PACKET_OUTGOING.
      * So, it is safe to (mis)use it to mark skbs on the error queue.
      */
     skb->pkt_type = PACKET_OUTGOING;
     BUILD_BUG_ON(PACKET_OUTGOING == 0);
 }
 
 /*
  * Note: We dont mem charge error packets (no sk_forward_alloc changes)
  */
 int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
 {
     if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
         (unsigned int)READ_ONCE(sk->sk_rcvbuf))
         return -ENOMEM;
 
     skb_orphan(skb);
     skb->sk = sk;
     skb->destructor = sock_rmem_free;
     atomic_add(skb->truesize, &sk->sk_rmem_alloc);
     skb_set_err_queue(skb);
 
     /* before exiting rcu section, make sure dst is refcounted */
     skb_dst_force(skb);
 
     skb_queue_tail(&sk->sk_error_queue, skb);
     if (!sock_flag(sk, SOCK_DEAD))
         sk_error_report(sk);
     return 0;
 }
 EXPORT_SYMBOL(sock_queue_err_skb);
 
 static bool is_icmp_err_skb(const struct sk_buff *skb)
 {
     return skb && (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
                SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ICMP6);
 }
 
 struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
 {
     struct sk_buff_head *q = &sk->sk_error_queue;
     struct sk_buff *skb, *skb_next = NULL;
     bool icmp_next = false;
     unsigned long flags;
 
     spin_lock_irqsave(&q->lock, flags);
     skb = __skb_dequeue(q);
     if (skb && (skb_next = skb_peek(q))) {
         icmp_next = is_icmp_err_skb(skb_next);
         if (icmp_next)
             sk->sk_err = SKB_EXT_ERR(skb_next)->ee.ee_errno;
     }
     spin_unlock_irqrestore(&q->lock, flags);
 
     if (is_icmp_err_skb(skb) && !icmp_next)
         sk->sk_err = 0;
 
     if (skb_next)
         sk_error_report(sk);
 
     return skb;
 }
 EXPORT_SYMBOL(sock_dequeue_err_skb);
 
 /**
  * skb_clone_sk - create clone of skb, and take reference to socket
  * @skb: the skb to clone
  *
  * This function creates a clone of a buffer that holds a reference on
  * sk_refcnt.  Buffers created via this function are meant to be
  * returned using sock_queue_err_skb, or free via kfree_skb.
  *
  * When passing buffers allocated with this function to sock_queue_err_skb
  * it is necessary to wrap the call with sock_hold/sock_put in order to
  * prevent the socket from being released prior to being enqueued on
  * the sk_error_queue.
  */
 struct sk_buff *skb_clone_sk(struct sk_buff *skb)
 {
     struct sock *sk = skb->sk;
     struct sk_buff *clone;
 
     if (!sk || !refcount_inc_not_zero(&sk->sk_refcnt))
         return NULL;
 
     clone = skb_clone(skb, GFP_ATOMIC);
     if (!clone) {
         sock_put(sk);
         return NULL;
     }
 
     clone->sk = sk;
     clone->destructor = sock_efree;
 
     return clone;
 }
 EXPORT_SYMBOL(skb_clone_sk);
 
 static void __skb_complete_tx_timestamp(struct sk_buff *skb,
                     struct sock *sk,
                     int tstype,
                     bool opt_stats)
 {
     struct sock_exterr_skb *serr;
     int err;
 
     BUILD_BUG_ON(sizeof(struct sock_exterr_skb) > sizeof(skb->cb));
 
     serr = SKB_EXT_ERR(skb);
     memset(serr, 0, sizeof(*serr));
     serr->ee.ee_errno = ENOMSG;
     serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
     serr->ee.ee_info = tstype;
     serr->opt_stats = opt_stats;
     serr->header.h4.iif = skb->dev ? skb->dev->ifindex : 0;
     if (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID) {
         serr->ee.ee_data = skb_shinfo(skb)->tskey;
         if (sk_is_tcp(sk))
             serr->ee.ee_data -= atomic_read(&sk->sk_tskey);
     }
 
     err = sock_queue_err_skb(sk, skb);
 
     if (err)
         kfree_skb(skb);
 }
 
 static bool skb_may_tx_timestamp(struct sock *sk, bool tsonly)
 {
     bool ret;
 
     if (likely(READ_ONCE(sysctl_tstamp_allow_data) || tsonly))
         return true;
 
     read_lock_bh(&sk->sk_callback_lock);
     ret = sk->sk_socket && sk->sk_socket->file &&
           file_ns_capable(sk->sk_socket->file, &init_user_ns, CAP_NET_RAW);
     read_unlock_bh(&sk->sk_callback_lock);
     return ret;
 }
 
 void skb_complete_tx_timestamp(struct sk_buff *skb,
                    struct skb_shared_hwtstamps *hwtstamps)
 {
     struct sock *sk = skb->sk;
 
     if (!skb_may_tx_timestamp(sk, false))
         goto err;
 
     /* Take a reference to prevent skb_orphan() from freeing the socket,
      * but only if the socket refcount is not zero.
      */
     if (likely(refcount_inc_not_zero(&sk->sk_refcnt))) {
         *skb_hwtstamps(skb) = *hwtstamps;
         __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND, false);
         sock_put(sk);
         return;
     }
 
 err:
     kfree_skb(skb);
 }
 EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
 
 void __skb_tstamp_tx(struct sk_buff *orig_skb,
              const struct sk_buff *ack_skb,
              struct skb_shared_hwtstamps *hwtstamps,
              struct sock *sk, int tstype)
 {
     struct sk_buff *skb;
     bool tsonly, opt_stats = false;
 
     if (!sk)
         return;
 
     if (!hwtstamps && !(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TX_SWHW) &&
         skb_shinfo(orig_skb)->tx_flags & SKBTX_IN_PROGRESS)
         return;
 
     tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
     if (!skb_may_tx_timestamp(sk, tsonly))
         return;
 
     if (tsonly) {
 #ifdef CONFIG_INET
         if ((sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS) &&
             sk_is_tcp(sk)) {
             skb = tcp_get_timestamping_opt_stats(sk, orig_skb,
                                  ack_skb);
             opt_stats = true;
         } else
 #endif
             skb = alloc_skb(0, GFP_ATOMIC);
     } else {
         skb = skb_clone(orig_skb, GFP_ATOMIC);
     }
     if (!skb)
         return;
 
     if (tsonly) {
         skb_shinfo(skb)->tx_flags |= skb_shinfo(orig_skb)->tx_flags &
                          SKBTX_ANY_TSTAMP;
         skb_shinfo(skb)->tskey = skb_shinfo(orig_skb)->tskey;
     }
 
     if (hwtstamps)
         *skb_hwtstamps(skb) = *hwtstamps;
     else
         __net_timestamp(skb);
 
     __skb_complete_tx_timestamp(skb, sk, tstype, opt_stats);
 }
 EXPORT_SYMBOL_GPL(__skb_tstamp_tx);
 
 void skb_tstamp_tx(struct sk_buff *orig_skb,
            struct skb_shared_hwtstamps *hwtstamps)
 {
     return __skb_tstamp_tx(orig_skb, NULL, hwtstamps, orig_skb->sk,
                    SCM_TSTAMP_SND);
 }
 EXPORT_SYMBOL_GPL(skb_tstamp_tx);
 
 void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
 {
     struct sock *sk = skb->sk;
     struct sock_exterr_skb *serr;
     int err = 1;
 
     skb->wifi_acked_valid = 1;
     skb->wifi_acked = acked;
 
     serr = SKB_EXT_ERR(skb);
     memset(serr, 0, sizeof(*serr));
     serr->ee.ee_errno = ENOMSG;
     serr->ee.ee_origin = SO_EE_ORIGIN_TXSTATUS;
 
     /* Take a reference to prevent skb_orphan() from freeing the socket,
      * but only if the socket refcount is not zero.
      */
     if (likely(refcount_inc_not_zero(&sk->sk_refcnt))) {
         err = sock_queue_err_skb(sk, skb);
         sock_put(sk);
     }
     if (err)
         kfree_skb(skb);
 }
 EXPORT_SYMBOL_GPL(skb_complete_wifi_ack);
 
 /**
  * skb_partial_csum_set - set up and verify partial csum values for packet
  * @skb: the skb to set
  * @start: the number of bytes after skb->data to start checksumming.
  * @off: the offset from start to place the checksum.
  *
  * For untrusted partially-checksummed packets, we need to make sure the values
  * for skb->csum_start and skb->csum_offset are valid so we don't oops.
  *
  * This function checks and sets those values and skb->ip_summed: if this
  * returns false you should drop the packet.
  */
 bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off)
 {
     u32 csum_end = (u32)start + (u32)off + sizeof(__sum16);
     u32 csum_start = skb_headroom(skb) + (u32)start;
 
     if (unlikely(csum_start > U16_MAX || csum_end > skb_headlen(skb))) {
         net_warn_ratelimited("bad partial csum: csum=%u/%u headroom=%u headlen=%u\n",
                      start, off, skb_headroom(skb), skb_headlen(skb));
         return false;
     }
     skb->ip_summed = CHECKSUM_PARTIAL;
     skb->csum_start = csum_start;
     skb->csum_offset = off;
     skb_set_transport_header(skb, start);
     return true;
 }
 EXPORT_SYMBOL_GPL(skb_partial_csum_set);
 
 static int skb_maybe_pull_tail(struct sk_buff *skb, unsigned int len,
                    unsigned int max)
 {
     if (skb_headlen(skb) >= len)
         return 0;
 
     /* If we need to pullup then pullup to the max, so we
      * won't need to do it again.
      */
     if (max > skb->len)
         max = skb->len;
 
     if (__pskb_pull_tail(skb, max - skb_headlen(skb)) == NULL)
         return -ENOMEM;
 
     if (skb_headlen(skb) < len)
         return -EPROTO;
 
     return 0;
 }
 
 #define MAX_TCP_HDR_LEN (15 * 4)
 
 static __sum16 *skb_checksum_setup_ip(struct sk_buff *skb,
                       typeof(IPPROTO_IP) proto,
                       unsigned int off)
 {
     int err;
 
     switch (proto) {
     case IPPROTO_TCP:
         err = skb_maybe_pull_tail(skb, off + sizeof(struct tcphdr),
                       off + MAX_TCP_HDR_LEN);
         if (!err && !skb_partial_csum_set(skb, off,
                           offsetof(struct tcphdr,
                                check)))
             err = -EPROTO;
         return err ? ERR_PTR(err) : &tcp_hdr(skb)->check;
 
     case IPPROTO_UDP:
         err = skb_maybe_pull_tail(skb, off + sizeof(struct udphdr),
                       off + sizeof(struct udphdr));
         if (!err && !skb_partial_csum_set(skb, off,
                           offsetof(struct udphdr,
                                check)))
             err = -EPROTO;
         return err ? ERR_PTR(err) : &udp_hdr(skb)->check;
     }
 
     return ERR_PTR(-EPROTO);
 }
 
 /* This value should be large enough to cover a tagged ethernet header plus
  * maximally sized IP and TCP or UDP headers.
  */
 #define MAX_IP_HDR_LEN 128
 
 static int skb_checksum_setup_ipv4(struct sk_buff *skb, bool recalculate)
 {
     unsigned int off;
     bool fragment;
     __sum16 *csum;
     int err;
 
     fragment = false;
 
     err = skb_maybe_pull_tail(skb,
                   sizeof(struct iphdr),
                   MAX_IP_HDR_LEN);
     if (err < 0)
         goto out;
 
     if (ip_is_fragment(ip_hdr(skb)))
         fragment = true;
 
     off = ip_hdrlen(skb);
 
     err = -EPROTO;
 
     if (fragment)
         goto out;
 
     csum = skb_checksum_setup_ip(skb, ip_hdr(skb)->protocol, off);
     if (IS_ERR(csum))
         return PTR_ERR(csum);
 
     if (recalculate)
         *csum = ~csum_tcpudp_magic(ip_hdr(skb)->saddr,
                        ip_hdr(skb)->daddr,
                        skb->len - off,
                        ip_hdr(skb)->protocol, 0);
     err = 0;
 
 out:
     return err;
 }
 
 /* This value should be large enough to cover a tagged ethernet header plus
  * an IPv6 header, all options, and a maximal TCP or UDP header.
  */
 #define MAX_IPV6_HDR_LEN 256
 
 #define OPT_HDR(type, skb, off) \
     (type *)(skb_network_header(skb) + (off))
 
 static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
 {
     int err;
     u8 nexthdr;
     unsigned int off;
     unsigned int len;
     bool fragment;
     bool done;
     __sum16 *csum;
 
     fragment = false;
     done = false;
 
     off = sizeof(struct ipv6hdr);
 
     err = skb_maybe_pull_tail(skb, off, MAX_IPV6_HDR_LEN);
     if (err < 0)
         goto out;
 
     nexthdr = ipv6_hdr(skb)->nexthdr;
 
     len = sizeof(struct ipv6hdr) + ntohs(ipv6_hdr(skb)->payload_len);
     while (off <= len && !done) {
         switch (nexthdr) {
         case IPPROTO_DSTOPTS:
         case IPPROTO_HOPOPTS:
         case IPPROTO_ROUTING: {
             struct ipv6_opt_hdr *hp;
 
             err = skb_maybe_pull_tail(skb,
                           off +
                           sizeof(struct ipv6_opt_hdr),
                           MAX_IPV6_HDR_LEN);
             if (err < 0)
                 goto out;
 
             hp = OPT_HDR(struct ipv6_opt_hdr, skb, off);
             nexthdr = hp->nexthdr;
             off += ipv6_optlen(hp);
             break;
         }
         case IPPROTO_AH: {
             struct ip_auth_hdr *hp;
 
             err = skb_maybe_pull_tail(skb,
                           off +
                           sizeof(struct ip_auth_hdr),
                           MAX_IPV6_HDR_LEN);
             if (err < 0)
                 goto out;
 
             hp = OPT_HDR(struct ip_auth_hdr, skb, off);
             nexthdr = hp->nexthdr;
             off += ipv6_authlen(hp);
             break;
         }
         case IPPROTO_FRAGMENT: {
             struct frag_hdr *hp;
 
             err = skb_maybe_pull_tail(skb,
                           off +
                           sizeof(struct frag_hdr),
                           MAX_IPV6_HDR_LEN);
             if (err < 0)
                 goto out;
 
             hp = OPT_HDR(struct frag_hdr, skb, off);
 
             if (hp->frag_off & htons(IP6_OFFSET | IP6_MF))
                 fragment = true;
 
             nexthdr = hp->nexthdr;
             off += sizeof(struct frag_hdr);
             break;
         }
         default:
             done = true;
             break;
         }
     }
 
     err = -EPROTO;
 
     if (!done || fragment)
         goto out;
 
     csum = skb_checksum_setup_ip(skb, nexthdr, off);
     if (IS_ERR(csum))
         return PTR_ERR(csum);
 
     if (recalculate)
         *csum = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
                      &ipv6_hdr(skb)->daddr,
                      skb->len - off, nexthdr, 0);
     err = 0;
 
 out:
     return err;
 }
 
 /**
  * skb_checksum_setup - set up partial checksum offset
  * @skb: the skb to set up
  * @recalculate: if true the pseudo-header checksum will be recalculated
  */
 int skb_checksum_setup(struct sk_buff *skb, bool recalculate)
 {
     int err;
 
     switch (skb->protocol) {
     case htons(ETH_P_IP):
         err = skb_checksum_setup_ipv4(skb, recalculate);
         break;
 
     case htons(ETH_P_IPV6):
         err = skb_checksum_setup_ipv6(skb, recalculate);
         break;
 
     default:
         err = -EPROTO;
         break;
     }
 
     return err;
 }
 EXPORT_SYMBOL(skb_checksum_setup);
 
 /**
  * skb_checksum_maybe_trim - maybe trims the given skb
  * @skb: the skb to check
  * @transport_len: the data length beyond the network header
  *
  * Checks whether the given skb has data beyond the given transport length.
  * If so, returns a cloned skb trimmed to this transport length.
  * Otherwise returns the provided skb. Returns NULL in error cases
  * (e.g. transport_len exceeds skb length or out-of-memory).
  *
  * Caller needs to set the skb transport header and free any returned skb if it
  * differs from the provided skb.
  */
 static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
                            unsigned int transport_len)
 {
     struct sk_buff *skb_chk;
     unsigned int len = skb_transport_offset(skb) + transport_len;
     int ret;
 
     if (skb->len < len)
         return NULL;
     else if (skb->len == len)
         return skb;
 
     skb_chk = skb_clone(skb, GFP_ATOMIC);
     if (!skb_chk)
         return NULL;
 
     ret = pskb_trim_rcsum(skb_chk, len);
     if (ret) {
         kfree_skb(skb_chk);
         return NULL;
     }
 
     return skb_chk;
 }
 
 /**
  * skb_checksum_trimmed - validate checksum of an skb
  * @skb: the skb to check
  * @transport_len: the data length beyond the network header
  * @skb_chkf: checksum function to use
  *
  * Applies the given checksum function skb_chkf to the provided skb.
  * Returns a checked and maybe trimmed skb. Returns NULL on error.
  *
  * If the skb has data beyond the given transport length, then a
  * trimmed & cloned skb is checked and returned.
  *
  * Caller needs to set the skb transport header and free any returned skb if it
  * differs from the provided skb.
  */
 struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
                      unsigned int transport_len,
                      __sum16(*skb_chkf)(struct sk_buff *skb))
 {
     struct sk_buff *skb_chk;
     unsigned int offset = skb_transport_offset(skb);
     __sum16 ret;
 
     skb_chk = skb_checksum_maybe_trim(skb, transport_len);
     if (!skb_chk)
         goto err;
 
     if (!pskb_may_pull(skb_chk, offset))
         goto err;
 
     skb_pull_rcsum(skb_chk, offset);
     ret = skb_chkf(skb_chk);
     skb_push_rcsum(skb_chk, offset);
 
     if (ret)
         goto err;
 
     return skb_chk;
 
 err:
     if (skb_chk && skb_chk != skb)
         kfree_skb(skb_chk);
 
     return NULL;
 
 }
 EXPORT_SYMBOL(skb_checksum_trimmed);
 
 void __skb_warn_lro_forwarding(const struct sk_buff *skb)
 {
     net_warn_ratelimited("%s: received packets cannot be forwarded while LRO is enabled\n",
                  skb->dev->name);
 }
 EXPORT_SYMBOL(__skb_warn_lro_forwarding);
 
 void kfree_skb_partial(struct sk_buff *skb, bool head_stolen)
 {
     if (head_stolen) {
         skb_release_head_state(skb);
         kmem_cache_free(skbuff_head_cache, skb);
     } else {
         __kfree_skb(skb);
     }
 }
 EXPORT_SYMBOL(kfree_skb_partial);
 
 /**
  * skb_try_coalesce - try to merge skb to prior one
  * @to: prior buffer
  * @from: buffer to add
  * @fragstolen: pointer to boolean
  * @delta_truesize: how much more was allocated than was requested
  */
 bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
               bool *fragstolen, int *delta_truesize)
 {
     struct skb_shared_info *to_shinfo, *from_shinfo;
     int i, delta, len = from->len;
 
     *fragstolen = false;
 
     if (skb_cloned(to))
         return false;
 
     /* In general, avoid mixing slab allocated and page_pool allocated
      * pages within the same SKB. However when @to is not pp_recycle and
      * @from is cloned, we can transition frag pages from page_pool to
      * reference counted.
      *
      * On the other hand, don't allow coalescing two pp_recycle SKBs if
      * @from is cloned, in case the SKB is using page_pool fragment
      * references (PP_FLAG_PAGE_FRAG). Since we only take full page
      * references for cloned SKBs at the moment that would result in
      * inconsistent reference counts.
      */
     if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))
         return false;
 
     if (len <= skb_tailroom(to)) {
         if (len)
             BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
         *delta_truesize = 0;
         return true;
     }
 
     to_shinfo = skb_shinfo(to);
     from_shinfo = skb_shinfo(from);
     if (to_shinfo->frag_list || from_shinfo->frag_list)
         return false;
     if (skb_zcopy(to) || skb_zcopy(from))
         return false;
 
     if (skb_headlen(from) != 0) {
         struct page *page;
         unsigned int offset;
 
         if (to_shinfo->nr_frags +
             from_shinfo->nr_frags >= MAX_SKB_FRAGS)
             return false;
 
         if (skb_head_is_locked(from))
             return false;
 
         delta = from->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
 
         page = virt_to_head_page(from->head);
         offset = from->data - (unsigned char *)page_address(page);
 
         skb_fill_page_desc(to, to_shinfo->nr_frags,
                    page, offset, skb_headlen(from));
         *fragstolen = true;
     } else {
         if (to_shinfo->nr_frags +
             from_shinfo->nr_frags > MAX_SKB_FRAGS)
             return false;
 
         delta = from->truesize - SKB_TRUESIZE(skb_end_offset(from));
     }
 
     WARN_ON_ONCE(delta < len);
 
     memcpy(to_shinfo->frags + to_shinfo->nr_frags,
            from_shinfo->frags,
            from_shinfo->nr_frags * sizeof(skb_frag_t));
     to_shinfo->nr_frags += from_shinfo->nr_frags;
 
     if (!skb_cloned(from))
         from_shinfo->nr_frags = 0;
 
     /* if the skb is not cloned this does nothing
      * since we set nr_frags to 0.
      */
     for (i = 0; i < from_shinfo->nr_frags; i++)
         __skb_frag_ref(&from_shinfo->frags[i]);
 
     to->truesize += delta;
     to->len += len;
     to->data_len += len;
 
     *delta_truesize = delta;
     return true;
 }
 EXPORT_SYMBOL(skb_try_coalesce);
 
 /**
  * skb_scrub_packet - scrub an skb
  *
  * @skb: buffer to clean
  * @xnet: packet is crossing netns
  *
  * skb_scrub_packet can be used after encapsulating or decapsulting a packet
  * into/from a tunnel. Some information have to be cleared during these
  * operations.
  * skb_scrub_packet can also be used to clean a skb before injecting it in
  * another namespace (@xnet == true). We have to clear all information in the
  * skb that could impact namespace isolation.
  */
 void skb_scrub_packet(struct sk_buff *skb, bool xnet)
 {
     skb->pkt_type = PACKET_HOST;
     skb->skb_iif = 0;
     skb->ignore_df = 0;
     skb_dst_drop(skb);
     skb_ext_reset(skb);
     nf_reset_ct(skb);
     nf_reset_trace(skb);
 
 #ifdef CONFIG_NET_SWITCHDEV
     skb->offload_fwd_mark = 0;
     skb->offload_l3_fwd_mark = 0;
 #endif
 
     if (!xnet)
         return;
 
     ipvs_reset(skb);
     skb->mark = 0;
     skb_clear_tstamp(skb);
 }
 EXPORT_SYMBOL_GPL(skb_scrub_packet);
 
 /**
  * skb_gso_transport_seglen - Return length of individual segments of a gso packet
  *
  * @skb: GSO skb
  *
  * skb_gso_transport_seglen is used to determine the real size of the
  * individual segments, including Layer4 headers (TCP/UDP).
  *
  * The MAC/L2 or network (IP, IPv6) headers are not accounted for.
  */
 static unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
 {
     const struct skb_shared_info *shinfo = skb_shinfo(skb);
     unsigned int thlen = 0;
 
     if (skb->encapsulation) {
         thlen = skb_inner_transport_header(skb) -
             skb_transport_header(skb);
 
         if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
             thlen += inner_tcp_hdrlen(skb);
     } else if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
         thlen = tcp_hdrlen(skb);
     } else if (unlikely(skb_is_gso_sctp(skb))) {
         thlen = sizeof(struct sctphdr);
     } else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
         thlen = sizeof(struct udphdr);
     }
     /* UFO sets gso_size to the size of the fragmentation
      * payload, i.e. the size of the L4 (UDP) header is already
      * accounted for.
      */
     return thlen + shinfo->gso_size;
 }
 
 /**
  * skb_gso_network_seglen - Return length of individual segments of a gso packet
  *
  * @skb: GSO skb
  *
  * skb_gso_network_seglen is used to determine the real size of the
  * individual segments, including Layer3 (IP, IPv6) and L4 headers (TCP/UDP).
  *
  * The MAC/L2 header is not accounted for.
  */
 static unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
 {
     unsigned int hdr_len = skb_transport_header(skb) -
                    skb_network_header(skb);
 
     return hdr_len + skb_gso_transport_seglen(skb);
 }
 
 /**
  * skb_gso_mac_seglen - Return length of individual segments of a gso packet
  *
  * @skb: GSO skb
  *
  * skb_gso_mac_seglen is used to determine the real size of the
  * individual segments, including MAC/L2, Layer3 (IP, IPv6) and L4
  * headers (TCP/UDP).
  */
 static unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
 {
     unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
 
     return hdr_len + skb_gso_transport_seglen(skb);
 }
 
 /**
  * skb_gso_size_check - check the skb size, considering GSO_BY_FRAGS
  *
  * There are a couple of instances where we have a GSO skb, and we
  * want to determine what size it would be after it is segmented.
  *
  * We might want to check:
  * -    L3+L4+payload size (e.g. IP forwarding)
  * - L2+L3+L4+payload size (e.g. sanity check before passing to driver)
  *
  * This is a helper to do that correctly considering GSO_BY_FRAGS.
  *
  * @skb: GSO skb
  *
  * @seg_len: The segmented length (from skb_gso_*_seglen). In the
  *           GSO_BY_FRAGS case this will be [header sizes + GSO_BY_FRAGS].
  *
  * @max_len: The maximum permissible length.
  *
  * Returns true if the segmented length <= max length.
  */
 static inline bool skb_gso_size_check(const struct sk_buff *skb,
                       unsigned int seg_len,
                       unsigned int max_len) {
     const struct skb_shared_info *shinfo = skb_shinfo(skb);
     const struct sk_buff *iter;
 
     if (shinfo->gso_size != GSO_BY_FRAGS)
         return seg_len <= max_len;
 
     /* Undo this so we can re-use header sizes */
     seg_len -= GSO_BY_FRAGS;
 
     skb_walk_frags(skb, iter) {
         if (seg_len + skb_headlen(iter) > max_len)
             return false;
     }
 
     return true;
 }
 
 /**
  * skb_gso_validate_network_len - Will a split GSO skb fit into a given MTU?
  *
  * @skb: GSO skb
  * @mtu: MTU to validate against
  *
  * skb_gso_validate_network_len validates if a given skb will fit a
  * wanted MTU once split. It considers L3 headers, L4 headers, and the
  * payload.
  */
 bool skb_gso_validate_network_len(const struct sk_buff *skb, unsigned int mtu)
 {
     return skb_gso_size_check(skb, skb_gso_network_seglen(skb), mtu);
 }
 EXPORT_SYMBOL_GPL(skb_gso_validate_network_len);
 
 /**
  * skb_gso_validate_mac_len - Will a split GSO skb fit in a given length?
  *
  * @skb: GSO skb
  * @len: length to validate against
  *
  * skb_gso_validate_mac_len validates if a given skb will fit a wanted
  * length once split, including L2, L3 and L4 headers and the payload.
  */
 bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len)
 {
     return skb_gso_size_check(skb, skb_gso_mac_seglen(skb), len);
 }
 EXPORT_SYMBOL_GPL(skb_gso_validate_mac_len);
 
 static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
 {
     int mac_len, meta_len;
     void *meta;
 
     if (skb_cow(skb, skb_headroom(skb)) < 0) {
         kfree_skb(skb);
         return NULL;
     }
 
     mac_len = skb->data - skb_mac_header(skb);
     if (likely(mac_len > VLAN_HLEN + ETH_TLEN)) {
         memmove(skb_mac_header(skb) + VLAN_HLEN, skb_mac_header(skb),
             mac_len - VLAN_HLEN - ETH_TLEN);
     }
 
     meta_len = skb_metadata_len(skb);
     if (meta_len) {
         meta = skb_metadata_end(skb) - meta_len;
         memmove(meta + VLAN_HLEN, meta, meta_len);
     }
 
     skb->mac_header += VLAN_HLEN;
     return skb;
 }
 
 struct sk_buff *skb_vlan_untag(struct sk_buff *skb)
 {
     struct vlan_hdr *vhdr;
     u16 vlan_tci;
 
     if (unlikely(skb_vlan_tag_present(skb))) {
         /* vlan_tci is already set-up so leave this for another time */
         return skb;
     }
 
     skb = skb_share_check(skb, GFP_ATOMIC);
     if (unlikely(!skb))
         goto err_free;
     /* We may access the two bytes after vlan_hdr in vlan_set_encap_proto(). */
     if (unlikely(!pskb_may_pull(skb, VLAN_HLEN + sizeof(unsigned short))))
         goto err_free;
 
     vhdr = (struct vlan_hdr *)skb->data;
     vlan_tci = ntohs(vhdr->h_vlan_TCI);
     __vlan_hwaccel_put_tag(skb, skb->protocol, vlan_tci);
 
     skb_pull_rcsum(skb, VLAN_HLEN);
     vlan_set_encap_proto(skb, vhdr);
 
     skb = skb_reorder_vlan_header(skb);
     if (unlikely(!skb))
         goto err_free;
 
     skb_reset_network_header(skb);
     if (!skb_transport_header_was_set(skb))
         skb_reset_transport_header(skb);
     skb_reset_mac_len(skb);
 
     return skb;
 
 err_free:
     kfree_skb(skb);
     return NULL;
 }
 EXPORT_SYMBOL(skb_vlan_untag);
 
 int skb_ensure_writable(struct sk_buff *skb, unsigned int write_len)
 {
     if (!pskb_may_pull(skb, write_len))
         return -ENOMEM;
 
     if (!skb_cloned(skb) || skb_clone_writable(skb, write_len))
         return 0;
 
     return pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
 }
 EXPORT_SYMBOL(skb_ensure_writable);
 
 /* remove VLAN header from packet and update csum accordingly.
  * expects a non skb_vlan_tag_present skb with a vlan tag payload
  */
 int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci)
 {
     struct vlan_hdr *vhdr;
     int offset = skb->data - skb_mac_header(skb);
     int err;
 
     if (WARN_ONCE(offset,
               "__skb_vlan_pop got skb with skb->data not at mac header (offset %d)\n",
               offset)) {
         return -EINVAL;
     }
 
     err = skb_ensure_writable(skb, VLAN_ETH_HLEN);
     if (unlikely(err))
         return err;
 
     skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
 
     vhdr = (struct vlan_hdr *)(skb->data + ETH_HLEN);
     *vlan_tci = ntohs(vhdr->h_vlan_TCI);
 
     memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
     __skb_pull(skb, VLAN_HLEN);
 
     vlan_set_encap_proto(skb, vhdr);
     skb->mac_header += VLAN_HLEN;
 
     if (skb_network_offset(skb) < ETH_HLEN)
         skb_set_network_header(skb, ETH_HLEN);
 
     skb_reset_mac_len(skb);
 
     return err;
 }
 EXPORT_SYMBOL(__skb_vlan_pop);
 
 /* Pop a vlan tag either from hwaccel or from payload.
  * Expects skb->data at mac header.
  */
 int skb_vlan_pop(struct sk_buff *skb)
 {
     u16 vlan_tci;
     __be16 vlan_proto;
     int err;
 
     if (likely(skb_vlan_tag_present(skb))) {
         __vlan_hwaccel_clear_tag(skb);
     } else {
         if (unlikely(!eth_type_vlan(skb->protocol)))
             return 0;
 
         err = __skb_vlan_pop(skb, &vlan_tci);
         if (err)
             return err;
     }
     /* move next vlan tag to hw accel tag */
     if (likely(!eth_type_vlan(skb->protocol)))
         return 0;
 
     vlan_proto = skb->protocol;
     err = __skb_vlan_pop(skb, &vlan_tci);
     if (unlikely(err))
         return err;
 
     __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
     return 0;
 }
 EXPORT_SYMBOL(skb_vlan_pop);
 
 /* Push a vlan tag either into hwaccel or into payload (if hwaccel tag present).
  * Expects skb->data at mac header.
  */
 int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 {
     if (skb_vlan_tag_present(skb)) {
         int offset = skb->data - skb_mac_header(skb);
         int err;
 
         if (WARN_ONCE(offset,
                   "skb_vlan_push got skb with skb->data not at mac header (offset %d)\n",
                   offset)) {
             return -EINVAL;
         }
 
         err = __vlan_insert_tag(skb, skb->vlan_proto,
                     skb_vlan_tag_get(skb));
         if (err)
             return err;
 
         skb->protocol = skb->vlan_proto;
         skb->mac_len += VLAN_HLEN;
 
         skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
     }
     __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
     return 0;
 }
 EXPORT_SYMBOL(skb_vlan_push);
 
 /**
  * skb_eth_pop() - Drop the Ethernet header at the head of a packet
  *
  * @skb: Socket buffer to modify
  *
  * Drop the Ethernet header of @skb.
  *
  * Expects that skb->data points to the mac header and that no VLAN tags are
  * present.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_eth_pop(struct sk_buff *skb)
 {
     if (!pskb_may_pull(skb, ETH_HLEN) || skb_vlan_tagged(skb) ||
         skb_network_offset(skb) < ETH_HLEN)
         return -EPROTO;
 
     skb_pull_rcsum(skb, ETH_HLEN);
     skb_reset_mac_header(skb);
     skb_reset_mac_len(skb);
 
     return 0;
 }
 EXPORT_SYMBOL(skb_eth_pop);
 
 /**
  * skb_eth_push() - Add a new Ethernet header at the head of a packet
  *
  * @skb: Socket buffer to modify
  * @dst: Destination MAC address of the new header
  * @src: Source MAC address of the new header
  *
  * Prepend @skb with a new Ethernet header.
  *
  * Expects that skb->data points to the mac header, which must be empty.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_eth_push(struct sk_buff *skb, const unsigned char *dst,
          const unsigned char *src)
 {
     struct ethhdr *eth;
     int err;
 
     if (skb_network_offset(skb) || skb_vlan_tag_present(skb))
         return -EPROTO;
 
     err = skb_cow_head(skb, sizeof(*eth));
     if (err < 0)
         return err;
 
     skb_push(skb, sizeof(*eth));
     skb_reset_mac_header(skb);
     skb_reset_mac_len(skb);
 
     eth = eth_hdr(skb);
     ether_addr_copy(eth->h_dest, dst);
     ether_addr_copy(eth->h_source, src);
     eth->h_proto = skb->protocol;
 
     skb_postpush_rcsum(skb, eth, sizeof(*eth));
 
     return 0;
 }
 EXPORT_SYMBOL(skb_eth_push);
 
 /* Update the ethertype of hdr and the skb csum value if required. */
 static void skb_mod_eth_type(struct sk_buff *skb, struct ethhdr *hdr,
                  __be16 ethertype)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE) {
         __be16 diff[] = { ~hdr->h_proto, ethertype };
 
         skb->csum = csum_partial((char *)diff, sizeof(diff), skb->csum);
     }
 
     hdr->h_proto = ethertype;
 }
 
 /**
  * skb_mpls_push() - push a new MPLS header after mac_len bytes from start of
  *                   the packet
  *
  * @skb: buffer
  * @mpls_lse: MPLS label stack entry to push
  * @mpls_proto: ethertype of the new MPLS header (expects 0x8847 or 0x8848)
  * @mac_len: length of the MAC header
  * @ethernet: flag to indicate if the resulting packet after skb_mpls_push is
  *            ethernet
  *
  * Expects skb->data at mac header.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
           int mac_len, bool ethernet)
 {
     struct mpls_shim_hdr *lse;
     int err;
 
     if (unlikely(!eth_p_mpls(mpls_proto)))
         return -EINVAL;
 
     /* Networking stack does not allow simultaneous Tunnel and MPLS GSO. */
     if (skb->encapsulation)
         return -EINVAL;
 
     err = skb_cow_head(skb, MPLS_HLEN);
     if (unlikely(err))
         return err;
 
     if (!skb->inner_protocol) {
         skb_set_inner_network_header(skb, skb_network_offset(skb));
         skb_set_inner_protocol(skb, skb->protocol);
     }
 
     skb_push(skb, MPLS_HLEN);
     memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
         mac_len);
     skb_reset_mac_header(skb);
     skb_set_network_header(skb, mac_len);
     skb_reset_mac_len(skb);
 
     lse = mpls_hdr(skb);
     lse->label_stack_entry = mpls_lse;
     skb_postpush_rcsum(skb, lse, MPLS_HLEN);
 
     if (ethernet && mac_len >= ETH_HLEN)
         skb_mod_eth_type(skb, eth_hdr(skb), mpls_proto);
     skb->protocol = mpls_proto;
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_mpls_push);
 
 /**
  * skb_mpls_pop() - pop the outermost MPLS header
  *
  * @skb: buffer
  * @next_proto: ethertype of header after popped MPLS header
  * @mac_len: length of the MAC header
  * @ethernet: flag to indicate if the packet is ethernet
  *
  * Expects skb->data at mac header.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
          bool ethernet)
 {
     int err;
 
     if (unlikely(!eth_p_mpls(skb->protocol)))
         return 0;
 
     err = skb_ensure_writable(skb, mac_len + MPLS_HLEN);
     if (unlikely(err))
         return err;
 
     skb_postpull_rcsum(skb, mpls_hdr(skb), MPLS_HLEN);
     memmove(skb_mac_header(skb) + MPLS_HLEN, skb_mac_header(skb),
         mac_len);
 
     __skb_pull(skb, MPLS_HLEN);
     skb_reset_mac_header(skb);
     skb_set_network_header(skb, mac_len);
 
     if (ethernet && mac_len >= ETH_HLEN) {
         struct ethhdr *hdr;
 
         /* use mpls_hdr() to get ethertype to account for VLANs. */
         hdr = (struct ethhdr *)((void *)mpls_hdr(skb) - ETH_HLEN);
         skb_mod_eth_type(skb, hdr, next_proto);
     }
     skb->protocol = next_proto;
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_mpls_pop);
 
 /**
  * skb_mpls_update_lse() - modify outermost MPLS header and update csum
  *
  * @skb: buffer
  * @mpls_lse: new MPLS label stack entry to update to
  *
  * Expects skb->data at mac header.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse)
 {
     int err;
 
     if (unlikely(!eth_p_mpls(skb->protocol)))
         return -EINVAL;
 
     err = skb_ensure_writable(skb, skb->mac_len + MPLS_HLEN);
     if (unlikely(err))
         return err;
 
     if (skb->ip_summed == CHECKSUM_COMPLETE) {
         __be32 diff[] = { ~mpls_hdr(skb)->label_stack_entry, mpls_lse };
 
         skb->csum = csum_partial((char *)diff, sizeof(diff), skb->csum);
     }
 
     mpls_hdr(skb)->label_stack_entry = mpls_lse;
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(skb_mpls_update_lse);
 
 /**
  * skb_mpls_dec_ttl() - decrement the TTL of the outermost MPLS header
  *
  * @skb: buffer
  *
  * Expects skb->data at mac header.
  *
  * Returns 0 on success, -errno otherwise.
  */
 int skb_mpls_dec_ttl(struct sk_buff *skb)
 {
     u32 lse;
     u8 ttl;
 
     if (unlikely(!eth_p_mpls(skb->protocol)))
         return -EINVAL;
 
     if (!pskb_may_pull(skb, skb_network_offset(skb) + MPLS_HLEN))
         return -ENOMEM;
 
     lse = be32_to_cpu(mpls_hdr(skb)->label_stack_entry);
     ttl = (lse & MPLS_LS_TTL_MASK) >> MPLS_LS_TTL_SHIFT;
     if (!--ttl)
         return -EINVAL;
 
     lse &= ~MPLS_LS_TTL_MASK;
     lse |= ttl << MPLS_LS_TTL_SHIFT;
 
     return skb_mpls_update_lse(skb, cpu_to_be32(lse));
 }
 EXPORT_SYMBOL_GPL(skb_mpls_dec_ttl);
 
 /**
  * alloc_skb_with_frags - allocate skb with page frags
  *
  * @header_len: size of linear part
  * @data_len: needed length in frags
  * @max_page_order: max page order desired.
  * @errcode: pointer to error code if any
  * @gfp_mask: allocation mask
  *
  * This can be used to allocate a paged skb, given a maximal order for frags.
  */
 struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
                      unsigned long data_len,
                      int max_page_order,
                      int *errcode,
                      gfp_t gfp_mask)
 {
     int npages = (data_len + (PAGE_SIZE - 1)) >> PAGE_SHIFT;
     unsigned long chunk;
     struct sk_buff *skb;
     struct page *page;
     int i;
 
     *errcode = -EMSGSIZE;
     /* Note this test could be relaxed, if we succeed to allocate
      * high order pages...
      */
     if (npages > MAX_SKB_FRAGS)
         return NULL;
 
     *errcode = -ENOBUFS;
     skb = alloc_skb(header_len, gfp_mask);
     if (!skb)
         return NULL;
 
     skb->truesize += npages << PAGE_SHIFT;
 
     for (i = 0; npages > 0; i++) {
         int order = max_page_order;
 
         while (order) {
             if (npages >= 1 << order) {
                 page = alloc_pages((gfp_mask & ~__GFP_DIRECT_RECLAIM) |
                            __GFP_COMP |
                            __GFP_NOWARN,
                            order);
                 if (page)
                     goto fill_page;
                 /* Do not retry other high order allocations */
                 order = 1;
                 max_page_order = 0;
             }
             order--;
         }
         page = alloc_page(gfp_mask);
         if (!page)
             goto failure;
 fill_page:
         chunk = min_t(unsigned long, data_len,
                   PAGE_SIZE << order);
         skb_fill_page_desc(skb, i, page, 0, chunk);
         data_len -= chunk;
         npages -= 1 << order;
     }
     return skb;
 
 failure:
     kfree_skb(skb);
     return NULL;
 }
 EXPORT_SYMBOL(alloc_skb_with_frags);
 
 /* carve out the first off bytes from skb when off < headlen */
 static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
                     const int headlen, gfp_t gfp_mask)
 {
     int i;
     int size = skb_end_offset(skb);
     int new_hlen = headlen - off;
     u8 *data;
 
     size = SKB_DATA_ALIGN(size);
 
     if (skb_pfmemalloc(skb))
         gfp_mask |= __GFP_MEMALLOC;
     data = kmalloc_reserve(size +
                    SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                    gfp_mask, NUMA_NO_NODE, NULL);
     if (!data)
         return -ENOMEM;
 
     size = SKB_WITH_OVERHEAD(ksize(data));
 
     /* Copy real data, and all frags */
     skb_copy_from_linear_data_offset(skb, off, data, new_hlen);
     skb->len -= off;
 
     memcpy((struct skb_shared_info *)(data + size),
            skb_shinfo(skb),
            offsetof(struct skb_shared_info,
             frags[skb_shinfo(skb)->nr_frags]));
     if (skb_cloned(skb)) {
         /* drop the old head gracefully */
         if (skb_orphan_frags(skb, gfp_mask)) {
             kfree(data);
             return -ENOMEM;
         }
         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
             skb_frag_ref(skb, i);
         if (skb_has_frag_list(skb))
             skb_clone_fraglist(skb);
         skb_release_data(skb);
     } else {
         /* we can reuse existing recount- all we did was
          * relocate values
          */
         skb_free_head(skb);
     }
 
     skb->head = data;
     skb->data = data;
     skb->head_frag = 0;
     skb_set_end_offset(skb, size);
     skb_set_tail_pointer(skb, skb_headlen(skb));
     skb_headers_offset_update(skb, 0);
     skb->cloned = 0;
     skb->hdr_len = 0;
     skb->nohdr = 0;
     atomic_set(&skb_shinfo(skb)->dataref, 1);
 
     return 0;
 }
 
 static int pskb_carve(struct sk_buff *skb, const u32 off, gfp_t gfp);
 
 /* carve out the first eat bytes from skb's frag_list. May recurse into
  * pskb_carve()
  */
 static int pskb_carve_frag_list(struct sk_buff *skb,
                 struct skb_shared_info *shinfo, int eat,
                 gfp_t gfp_mask)
 {
     struct sk_buff *list = shinfo->frag_list;
     struct sk_buff *clone = NULL;
     struct sk_buff *insp = NULL;
 
     do {
         if (!list) {
             pr_err("Not enough bytes to eat. Want %d\n", eat);
             return -EFAULT;
         }
         if (list->len <= eat) {
             /* Eaten as whole. */
             eat -= list->len;
             list = list->next;
             insp = list;
         } else {
             /* Eaten partially. */
             if (skb_shared(list)) {
                 clone = skb_clone(list, gfp_mask);
                 if (!clone)
                     return -ENOMEM;
                 insp = list->next;
                 list = clone;
             } else {
                 /* This may be pulled without problems. */
                 insp = list;
             }
             if (pskb_carve(list, eat, gfp_mask) < 0) {
                 kfree_skb(clone);
                 return -ENOMEM;
             }
             break;
         }
     } while (eat);
 
     /* Free pulled out fragments. */
     while ((list = shinfo->frag_list) != insp) {
         shinfo->frag_list = list->next;
         consume_skb(list);
     }
     /* And insert new clone at head. */
     if (clone) {
         clone->next = list;
         shinfo->frag_list = clone;
     }
     return 0;
 }
 
 /* carve off first len bytes from skb. Split line (off) is in the
  * non-linear part of skb
  */
 static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
                        int pos, gfp_t gfp_mask)
 {
     int i, k = 0;
     int size = skb_end_offset(skb);
     u8 *data;
     const int nfrags = skb_shinfo(skb)->nr_frags;
     struct skb_shared_info *shinfo;
 
     size = SKB_DATA_ALIGN(size);
 
     if (skb_pfmemalloc(skb))
         gfp_mask |= __GFP_MEMALLOC;
     data = kmalloc_reserve(size +
                    SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                    gfp_mask, NUMA_NO_NODE, NULL);
     if (!data)
         return -ENOMEM;
 
     size = SKB_WITH_OVERHEAD(ksize(data));
 
     memcpy((struct skb_shared_info *)(data + size),
            skb_shinfo(skb), offsetof(struct skb_shared_info, frags[0]));
     if (skb_orphan_frags(skb, gfp_mask)) {
         kfree(data);
         return -ENOMEM;
     }
     shinfo = (struct skb_shared_info *)(data + size);
     for (i = 0; i < nfrags; i++) {
         int fsize = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 
         if (pos + fsize > off) {
             shinfo->frags[k] = skb_shinfo(skb)->frags[i];
 
             if (pos < off) {
                 /* Split frag.
                  * We have two variants in this case:
                  * 1. Move all the frag to the second
                  *    part, if it is possible. F.e.
                  *    this approach is mandatory for TUX,
                  *    where splitting is expensive.
                  * 2. Split is accurately. We make this.
                  */
                 skb_frag_off_add(&shinfo->frags[0], off - pos);
                 skb_frag_size_sub(&shinfo->frags[0], off - pos);
             }
             skb_frag_ref(skb, i);
             k++;
         }
         pos += fsize;
     }
     shinfo->nr_frags = k;
     if (skb_has_frag_list(skb))
         skb_clone_fraglist(skb);
 
     /* split line is in frag list */
     if (k == 0 && pskb_carve_frag_list(skb, shinfo, off - pos, gfp_mask)) {
         /* skb_frag_unref() is not needed here as shinfo->nr_frags = 0. */
         if (skb_has_frag_list(skb))
             kfree_skb_list(skb_shinfo(skb)->frag_list);
         kfree(data);
         return -ENOMEM;
     }
     skb_release_data(skb);
 
     skb->head = data;
     skb->head_frag = 0;
     skb->data = data;
     skb_set_end_offset(skb, size);
     skb_reset_tail_pointer(skb);
     skb_headers_offset_update(skb, 0);
     skb->cloned   = 0;
     skb->hdr_len  = 0;
     skb->nohdr    = 0;
     skb->len -= off;
     skb->data_len = skb->len;
     atomic_set(&skb_shinfo(skb)->dataref, 1);
     return 0;
 }
 
 /* remove len bytes from the beginning of the skb */
 static int pskb_carve(struct sk_buff *skb, const u32 len, gfp_t gfp)
 {
     int headlen = skb_headlen(skb);
 
     if (len < headlen)
         return pskb_carve_inside_header(skb, len, headlen, gfp);
     else
         return pskb_carve_inside_nonlinear(skb, len, headlen, gfp);
 }
 
 /* Extract to_copy bytes starting at off from skb, and return this in
  * a new skb
  */
 struct sk_buff *pskb_extract(struct sk_buff *skb, int off,
                  int to_copy, gfp_t gfp)
 {
     struct sk_buff  *clone = skb_clone(skb, gfp);
 
     if (!clone)
         return NULL;
 
     if (pskb_carve(clone, off, gfp) < 0 ||
         pskb_trim(clone, to_copy)) {
         kfree_skb(clone);
         return NULL;
     }
     return clone;
 }
 EXPORT_SYMBOL(pskb_extract);
 
 /**
  * skb_condense - try to get rid of fragments/frag_list if possible
  * @skb: buffer
  *
  * Can be used to save memory before skb is added to a busy queue.
  * If packet has bytes in frags and enough tail room in skb->head,
  * pull all of them, so that we can free the frags right now and adjust
  * truesize.
  * Notes:
  *  We do not reallocate skb->head thus can not fail.
  *  Caller must re-evaluate skb->truesize if needed.
  */
 void skb_condense(struct sk_buff *skb)
 {
     if (skb->data_len) {
         if (skb->data_len > skb->end - skb->tail ||
             skb_cloned(skb))
             return;
 
         /* Nice, we can free page frag(s) right now */
         __pskb_pull_tail(skb, skb->data_len);
     }
     /* At this point, skb->truesize might be over estimated,
      * because skb had a fragment, and fragments do not tell
      * their truesize.
      * When we pulled its content into skb->head, fragment
      * was freed, but __pskb_pull_tail() could not possibly
      * adjust skb->truesize, not knowing the frag truesize.
      */
     skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
 }
 
 #ifdef CONFIG_SKB_EXTENSIONS
 static void *skb_ext_get_ptr(struct skb_ext *ext, enum skb_ext_id id)
 {
     return (void *)ext + (ext->offset[id] * SKB_EXT_ALIGN_VALUE);
 }
 
 /**
  * __skb_ext_alloc - allocate a new skb extensions storage
  *
  * @flags: See kmalloc().
  *
  * Returns the newly allocated pointer. The pointer can later attached to a
  * skb via __skb_ext_set().
  * Note: caller must handle the skb_ext as an opaque data.
  */
 struct skb_ext *__skb_ext_alloc(gfp_t flags)
 {
     struct skb_ext *new = kmem_cache_alloc(skbuff_ext_cache, flags);
 
     if (new) {
         memset(new->offset, 0, sizeof(new->offset));
         refcount_set(&new->refcnt, 1);
     }
 
     return new;
 }
 
 static struct skb_ext *skb_ext_maybe_cow(struct skb_ext *old,
                      unsigned int old_active)
 {
     struct skb_ext *new;
 
     if (refcount_read(&old->refcnt) == 1)
         return old;
 
     new = kmem_cache_alloc(skbuff_ext_cache, GFP_ATOMIC);
     if (!new)
         return NULL;
 
     memcpy(new, old, old->chunks * SKB_EXT_ALIGN_VALUE);
     refcount_set(&new->refcnt, 1);
 
 #ifdef CONFIG_XFRM
     if (old_active & (1 << SKB_EXT_SEC_PATH)) {
         struct sec_path *sp = skb_ext_get_ptr(old, SKB_EXT_SEC_PATH);
         unsigned int i;
 
         for (i = 0; i < sp->len; i++)
             xfrm_state_hold(sp->xvec[i]);
     }
 #endif
     __skb_ext_put(old);
     return new;
 }
 
 /**
  * __skb_ext_set - attach the specified extension storage to this skb
  * @skb: buffer
  * @id: extension id
  * @ext: extension storage previously allocated via __skb_ext_alloc()
  *
  * Existing extensions, if any, are cleared.
  *
  * Returns the pointer to the extension.
  */
 void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
             struct skb_ext *ext)
 {
     unsigned int newlen, newoff = SKB_EXT_CHUNKSIZEOF(*ext);
 
     skb_ext_put(skb);
     newlen = newoff + skb_ext_type_len[id];
     ext->chunks = newlen;
     ext->offset[id] = newoff;
     skb->extensions = ext;
     skb->active_extensions = 1 << id;
     return skb_ext_get_ptr(ext, id);
 }
 
 /**
  * skb_ext_add - allocate space for given extension, COW if needed
  * @skb: buffer
  * @id: extension to allocate space for
  *
  * Allocates enough space for the given extension.
  * If the extension is already present, a pointer to that extension
  * is returned.
  *
  * If the skb was cloned, COW applies and the returned memory can be
  * modified without changing the extension space of clones buffers.
  *
  * Returns pointer to the extension or NULL on allocation failure.
  */
 void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
 {
     struct skb_ext *new, *old = NULL;
     unsigned int newlen, newoff;
 
     if (skb->active_extensions) {
         old = skb->extensions;
 
         new = skb_ext_maybe_cow(old, skb->active_extensions);
         if (!new)
             return NULL;
 
         if (__skb_ext_exist(new, id))
             goto set_active;
 
         newoff = new->chunks;
     } else {
         newoff = SKB_EXT_CHUNKSIZEOF(*new);
 
         new = __skb_ext_alloc(GFP_ATOMIC);
         if (!new)
             return NULL;
     }
 
     newlen = newoff + skb_ext_type_len[id];
     new->chunks = newlen;
     new->offset[id] = newoff;
 set_active:
     skb->slow_gro = 1;
     skb->extensions = new;
     skb->active_extensions |= 1 << id;
     return skb_ext_get_ptr(new, id);
 }
 EXPORT_SYMBOL(skb_ext_add);
 
 #ifdef CONFIG_XFRM
 static void skb_ext_put_sp(struct sec_path *sp)
 {
     unsigned int i;
 
     for (i = 0; i < sp->len; i++)
         xfrm_state_put(sp->xvec[i]);
 }
 #endif
 
 #ifdef CONFIG_MCTP_FLOWS
 static void skb_ext_put_mctp(struct mctp_flow *flow)
 {
     if (flow->key)
         mctp_key_unref(flow->key);
 }
 #endif
 
 void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
 {
     struct skb_ext *ext = skb->extensions;
 
     skb->active_extensions &= ~(1 << id);
     if (skb->active_extensions == 0) {
         skb->extensions = NULL;
         __skb_ext_put(ext);
 #ifdef CONFIG_XFRM
     } else if (id == SKB_EXT_SEC_PATH &&
            refcount_read(&ext->refcnt) == 1) {
         struct sec_path *sp = skb_ext_get_ptr(ext, SKB_EXT_SEC_PATH);
 
         skb_ext_put_sp(sp);
         sp->len = 0;
 #endif
     }
 }
 EXPORT_SYMBOL(__skb_ext_del);
 
 void __skb_ext_put(struct skb_ext *ext)
 {
     /* If this is last clone, nothing can increment
      * it after check passes.  Avoids one atomic op.
      */
     if (refcount_read(&ext->refcnt) == 1)
         goto free_now;
 
     if (!refcount_dec_and_test(&ext->refcnt))
         return;
 free_now:
 #ifdef CONFIG_XFRM
     if (__skb_ext_exist(ext, SKB_EXT_SEC_PATH))
         skb_ext_put_sp(skb_ext_get_ptr(ext, SKB_EXT_SEC_PATH));
 #endif
 #ifdef CONFIG_MCTP_FLOWS
     if (__skb_ext_exist(ext, SKB_EXT_MCTP))
         skb_ext_put_mctp(skb_ext_get_ptr(ext, SKB_EXT_MCTP));
 #endif
 
     kmem_cache_free(skbuff_ext_cache, ext);
 }
 EXPORT_SYMBOL(__skb_ext_put);
 #endif /* CONFIG_SKB_EXTENSIONS */
 
 /**
  * skb_attempt_defer_free - queue skb for remote freeing
  * @skb: buffer
  *
  * Put @skb in a per-cpu list, using the cpu which
  * allocated the skb/pages to reduce false sharing
  * and memory zone spinlock contention.
  */
 void skb_attempt_defer_free(struct sk_buff *skb)
 {
     int cpu = skb->alloc_cpu;
     struct softnet_data *sd;
     unsigned long flags;
     unsigned int defer_max;
     bool kick;
 
     if (WARN_ON_ONCE(cpu >= nr_cpu_ids) ||
         !cpu_online(cpu) ||
         cpu == raw_smp_processor_id()) {
 nodefer:    __kfree_skb(skb);
         return;
     }
 
     sd = &per_cpu(softnet_data, cpu);
     defer_max = READ_ONCE(sysctl_skb_defer_max);
     if (READ_ONCE(sd->defer_count) >= defer_max)
         goto nodefer;
 
     spin_lock_irqsave(&sd->defer_lock, flags);
     /* Send an IPI every time queue reaches half capacity. */
     kick = sd->defer_count == (defer_max >> 1);
     /* Paired with the READ_ONCE() few lines above */
     WRITE_ONCE(sd->defer_count, sd->defer_count + 1);
 
     skb->next = sd->defer_list;
     /* Paired with READ_ONCE() in skb_defer_free_flush() */
     WRITE_ONCE(sd->defer_list, skb);
     spin_unlock_irqrestore(&sd->defer_lock, flags);
 
     /* Make sure to trigger NET_RX_SOFTIRQ on the remote CPU
      * if we are unlucky enough (this seems very unlikely).
      */
     if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1))
         smp_call_function_single_async(cpu, &sd->defer_csd);
 }