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 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  *  Definitions for the 'struct sk_buff' memory handlers.
  *
  *  Authors:
  *      Alan Cox, <gw4pts@gw4pts.ampr.org>
  *      Florian La Roche, <rzsfl@rz.uni-sb.de>
  */
 
 #ifndef _LINUX_SKBUFF_H
 #define _LINUX_SKBUFF_H
 
 #include <linux/kernel.h>
 #include <linux/compiler.h>
 #include <linux/time.h>
 #include <linux/bug.h>
 #include <linux/bvec.h>
 #include <linux/cache.h>
 #include <linux/rbtree.h>
 #include <linux/socket.h>
 #include <linux/refcount.h>
 
 #include <linux/atomic.h>
 #include <asm/types.h>
 #include <linux/spinlock.h>
 #include <linux/net.h>
 #include <linux/textsearch.h>
 #include <net/checksum.h>
 #include <linux/rcupdate.h>
 #include <linux/hrtimer.h>
 #include <linux/dma-mapping.h>
 #include <linux/netdev_features.h>
 #include <linux/sched.h>
 #include <linux/sched/clock.h>
 #include <net/flow_dissector.h>
 #include <linux/splice.h>
 #include <linux/in6.h>
 #include <linux/if_packet.h>
 #include <linux/llist.h>
 #include <net/flow.h>
 #include <net/page_pool.h>
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 #include <linux/netfilter/nf_conntrack_common.h>
 #endif
 #include <net/net_debug.h>
 #include <net/dropreason.h>
 
 /**
  * DOC: skb checksums
  *
  * The interface for checksum offload between the stack and networking drivers
  * is as follows...
  *
  * IP checksum related features
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  *
  * Drivers advertise checksum offload capabilities in the features of a device.
  * From the stack's point of view these are capabilities offered by the driver.
  * A driver typically only advertises features that it is capable of offloading
  * to its device.
  *
  * .. flat-table:: Checksum related device features
  *   :widths: 1 10
  *
  *   * - %NETIF_F_HW_CSUM
  *     - The driver (or its device) is able to compute one
  *   IP (one's complement) checksum for any combination
  *   of protocols or protocol layering. The checksum is
  *   computed and set in a packet per the CHECKSUM_PARTIAL
  *   interface (see below).
  *
  *   * - %NETIF_F_IP_CSUM
  *     - Driver (device) is only able to checksum plain
  *   TCP or UDP packets over IPv4. These are specifically
  *   unencapsulated packets of the form IPv4|TCP or
  *   IPv4|UDP where the Protocol field in the IPv4 header
  *   is TCP or UDP. The IPv4 header may contain IP options.
  *   This feature cannot be set in features for a device
  *   with NETIF_F_HW_CSUM also set. This feature is being
  *   DEPRECATED (see below).
  *
  *   * - %NETIF_F_IPV6_CSUM
  *     - Driver (device) is only able to checksum plain
  *   TCP or UDP packets over IPv6. These are specifically
  *   unencapsulated packets of the form IPv6|TCP or
  *   IPv6|UDP where the Next Header field in the IPv6
  *   header is either TCP or UDP. IPv6 extension headers
  *   are not supported with this feature. This feature
  *   cannot be set in features for a device with
  *   NETIF_F_HW_CSUM also set. This feature is being
  *   DEPRECATED (see below).
  *
  *   * - %NETIF_F_RXCSUM
  *     - Driver (device) performs receive checksum offload.
  *   This flag is only used to disable the RX checksum
  *   feature for a device. The stack will accept receive
  *   checksum indication in packets received on a device
  *   regardless of whether NETIF_F_RXCSUM is set.
  *
  * Checksumming of received packets by device
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  *
  * Indication of checksum verification is set in &sk_buff.ip_summed.
  * Possible values are:
  *
  * - %CHECKSUM_NONE
  *
  *   Device did not checksum this packet e.g. due to lack of capabilities.
  *   The packet contains full (though not verified) checksum in packet but
  *   not in skb->csum. Thus, skb->csum is undefined in this case.
  *
  * - %CHECKSUM_UNNECESSARY
  *
  *   The hardware you're dealing with doesn't calculate the full checksum
  *   (as in %CHECKSUM_COMPLETE), but it does parse headers and verify checksums
  *   for specific protocols. For such packets it will set %CHECKSUM_UNNECESSARY
  *   if their checksums are okay. &sk_buff.csum is still undefined in this case
  *   though. A driver or device must never modify the checksum field in the
  *   packet even if checksum is verified.
  *
  *   %CHECKSUM_UNNECESSARY is applicable to following protocols:
  *
  *     - TCP: IPv6 and IPv4.
  *     - UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a
  *       zero UDP checksum for either IPv4 or IPv6, the networking stack
  *       may perform further validation in this case.
  *     - GRE: only if the checksum is present in the header.
  *     - SCTP: indicates the CRC in SCTP header has been validated.
  *     - FCOE: indicates the CRC in FC frame has been validated.
  *
  *   &sk_buff.csum_level indicates the number of consecutive checksums found in
  *   the packet minus one that have been verified as %CHECKSUM_UNNECESSARY.
  *   For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet
  *   and a device is able to verify the checksums for UDP (possibly zero),
  *   GRE (checksum flag is set) and TCP, &sk_buff.csum_level would be set to
  *   two. If the device were only able to verify the UDP checksum and not
  *   GRE, either because it doesn't support GRE checksum or because GRE
  *   checksum is bad, skb->csum_level would be set to zero (TCP checksum is
  *   not considered in this case).
  *
  * - %CHECKSUM_COMPLETE
  *
  *   This is the most generic way. The device supplied checksum of the _whole_
  *   packet as seen by netif_rx() and fills in &sk_buff.csum. This means the
  *   hardware doesn't need to parse L3/L4 headers to implement this.
  *
  *   Notes:
  *
  *   - Even if device supports only some protocols, but is able to produce
  *     skb->csum, it MUST use CHECKSUM_COMPLETE, not CHECKSUM_UNNECESSARY.
  *   - CHECKSUM_COMPLETE is not applicable to SCTP and FCoE protocols.
  *
  * - %CHECKSUM_PARTIAL
  *
  *   A checksum is set up to be offloaded to a device as described in the
  *   output description for CHECKSUM_PARTIAL. This may occur on a packet
  *   received directly from another Linux OS, e.g., a virtualized Linux kernel
  *   on the same host, or it may be set in the input path in GRO or remote
  *   checksum offload. For the purposes of checksum verification, the checksum
  *   referred to by skb->csum_start + skb->csum_offset and any preceding
  *   checksums in the packet are considered verified. Any checksums in the
  *   packet that are after the checksum being offloaded are not considered to
  *   be verified.
  *
  * Checksumming on transmit for non-GSO
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  *
  * The stack requests checksum offload in the &sk_buff.ip_summed for a packet.
  * Values are:
  *
  * - %CHECKSUM_PARTIAL
  *
  *   The driver is required to checksum the packet as seen by hard_start_xmit()
  *   from &sk_buff.csum_start up to the end, and to record/write the checksum at
  *   offset &sk_buff.csum_start + &sk_buff.csum_offset.
  *   A driver may verify that the
  *   csum_start and csum_offset values are valid values given the length and
  *   offset of the packet, but it should not attempt to validate that the
  *   checksum refers to a legitimate transport layer checksum -- it is the
  *   purview of the stack to validate that csum_start and csum_offset are set
  *   correctly.
  *
  *   When the stack requests checksum offload for a packet, the driver MUST
  *   ensure that the checksum is set correctly. A driver can either offload the
  *   checksum calculation to the device, or call skb_checksum_help (in the case
  *   that the device does not support offload for a particular checksum).
  *
  *   %NETIF_F_IP_CSUM and %NETIF_F_IPV6_CSUM are being deprecated in favor of
  *   %NETIF_F_HW_CSUM. New devices should use %NETIF_F_HW_CSUM to indicate
  *   checksum offload capability.
  *   skb_csum_hwoffload_help() can be called to resolve %CHECKSUM_PARTIAL based
  *   on network device checksumming capabilities: if a packet does not match
  *   them, skb_checksum_help() or skb_crc32c_help() (depending on the value of
  *   &sk_buff.csum_not_inet, see :ref:`crc`)
  *   is called to resolve the checksum.
  *
  * - %CHECKSUM_NONE
  *
  *   The skb was already checksummed by the protocol, or a checksum is not
  *   required.
  *
  * - %CHECKSUM_UNNECESSARY
  *
  *   This has the same meaning as CHECKSUM_NONE for checksum offload on
  *   output.
  *
  * - %CHECKSUM_COMPLETE
  *
  *   Not used in checksum output. If a driver observes a packet with this value
  *   set in skbuff, it should treat the packet as if %CHECKSUM_NONE were set.
  *
  * .. _crc:
  *
  * Non-IP checksum (CRC) offloads
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  *
  * .. flat-table::
  *   :widths: 1 10
  *
  *   * - %NETIF_F_SCTP_CRC
  *     - This feature indicates that a device is capable of
  *   offloading the SCTP CRC in a packet. To perform this offload the stack
  *   will set csum_start and csum_offset accordingly, set ip_summed to
  *   %CHECKSUM_PARTIAL and set csum_not_inet to 1, to provide an indication
  *   in the skbuff that the %CHECKSUM_PARTIAL refers to CRC32c.
  *   A driver that supports both IP checksum offload and SCTP CRC32c offload
  *   must verify which offload is configured for a packet by testing the
  *   value of &sk_buff.csum_not_inet; skb_crc32c_csum_help() is provided to
  *   resolve %CHECKSUM_PARTIAL on skbs where csum_not_inet is set to 1.
  *
  *   * - %NETIF_F_FCOE_CRC
  *     - This feature indicates that a device is capable of offloading the FCOE
  *   CRC in a packet. To perform this offload the stack will set ip_summed
  *   to %CHECKSUM_PARTIAL and set csum_start and csum_offset
  *   accordingly. Note that there is no indication in the skbuff that the
  *   %CHECKSUM_PARTIAL refers to an FCOE checksum, so a driver that supports
  *   both IP checksum offload and FCOE CRC offload must verify which offload
  *   is configured for a packet, presumably by inspecting packet headers.
  *
  * Checksumming on output with GSO
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  *
  * In the case of a GSO packet (skb_is_gso() is true), checksum offload
  * is implied by the SKB_GSO_* flags in gso_type. Most obviously, if the
  * gso_type is %SKB_GSO_TCPV4 or %SKB_GSO_TCPV6, TCP checksum offload as
  * part of the GSO operation is implied. If a checksum is being offloaded
  * with GSO then ip_summed is %CHECKSUM_PARTIAL, and both csum_start and
  * csum_offset are set to refer to the outermost checksum being offloaded
  * (two offloaded checksums are possible with UDP encapsulation).
  */
 
 /* Don't change this without changing skb_csum_unnecessary! */
 #define CHECKSUM_NONE       0
 #define CHECKSUM_UNNECESSARY    1
 #define CHECKSUM_COMPLETE   2
 #define CHECKSUM_PARTIAL    3
 
 /* Maximum value in skb->csum_level */
 #define SKB_MAX_CSUM_LEVEL  3
 
 #define SKB_DATA_ALIGN(X)   ALIGN(X, SMP_CACHE_BYTES)
 #define SKB_WITH_OVERHEAD(X)    \
     ((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
 #define SKB_MAX_ORDER(X, ORDER) \
     SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X))
 #define SKB_MAX_HEAD(X)     (SKB_MAX_ORDER((X), 0))
 #define SKB_MAX_ALLOC       (SKB_MAX_ORDER(0, 2))
 
 /* return minimum truesize of one skb containing X bytes of data */
 #define SKB_TRUESIZE(X) ((X) +                      \
              SKB_DATA_ALIGN(sizeof(struct sk_buff)) +   \
              SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
 
 struct ahash_request;
 struct net_device;
 struct scatterlist;
 struct pipe_inode_info;
 struct iov_iter;
 struct napi_struct;
 struct bpf_prog;
 union bpf_attr;
 struct skb_ext;
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 struct nf_bridge_info {
     enum {
         BRNF_PROTO_UNCHANGED,
         BRNF_PROTO_8021Q,
         BRNF_PROTO_PPPOE
     } orig_proto:8;
     u8          pkt_otherhost:1;
     u8          in_prerouting:1;
     u8          bridged_dnat:1;
     __u16           frag_max_size;
     struct net_device   *physindev;
 
     /* always valid & non-NULL from FORWARD on, for physdev match */
     struct net_device   *physoutdev;
     union {
         /* prerouting: detect dnat in orig/reply direction */
         __be32          ipv4_daddr;
         struct in6_addr ipv6_daddr;
 
         /* after prerouting + nat detected: store original source
          * mac since neigh resolution overwrites it, only used while
          * skb is out in neigh layer.
          */
         char neigh_header[8];
     };
 };
 #endif
 
 #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
 /* Chain in tc_skb_ext will be used to share the tc chain with
  * ovs recirc_id. It will be set to the current chain by tc
  * and read by ovs to recirc_id.
  */
 struct tc_skb_ext {
     __u32 chain;
     __u16 mru;
     __u16 zone;
     u8 post_ct:1;
     u8 post_ct_snat:1;
     u8 post_ct_dnat:1;
 };
 #endif
 
 struct sk_buff_head {
     /* These two members must be first to match sk_buff. */
     struct_group_tagged(sk_buff_list, list,
         struct sk_buff  *next;
         struct sk_buff  *prev;
     );
 
     __u32       qlen;
     spinlock_t  lock;
 };
 
 struct sk_buff;
 
 /* To allow 64K frame to be packed as single skb without frag_list we
  * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
  * buffers which do not start on a page boundary.
  *
  * Since GRO uses frags we allocate at least 16 regardless of page
  * size.
  */
 #if (65536/PAGE_SIZE + 1) < 16
 #define MAX_SKB_FRAGS 16UL
 #else
 #define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
 #endif
 extern int sysctl_max_skb_frags;
 
 /* Set skb_shinfo(skb)->gso_size to this in case you want skb_segment to
  * segment using its current segmentation instead.
  */
 #define GSO_BY_FRAGS    0xFFFF
 
 typedef struct bio_vec skb_frag_t;
 
 /**
  * skb_frag_size() - Returns the size of a skb fragment
  * @frag: skb fragment
  */
 static inline unsigned int skb_frag_size(const skb_frag_t *frag)
 {
     return frag->bv_len;
 }
 
 /**
  * skb_frag_size_set() - Sets the size of a skb fragment
  * @frag: skb fragment
  * @size: size of fragment
  */
 static inline void skb_frag_size_set(skb_frag_t *frag, unsigned int size)
 {
     frag->bv_len = size;
 }
 
 /**
  * skb_frag_size_add() - Increments the size of a skb fragment by @delta
  * @frag: skb fragment
  * @delta: value to add
  */
 static inline void skb_frag_size_add(skb_frag_t *frag, int delta)
 {
     frag->bv_len += delta;
 }
 
 /**
  * skb_frag_size_sub() - Decrements the size of a skb fragment by @delta
  * @frag: skb fragment
  * @delta: value to subtract
  */
 static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
 {
     frag->bv_len -= delta;
 }
 
 /**
  * skb_frag_must_loop - Test if %p is a high memory page
  * @p: fragment's page
  */
 static inline bool skb_frag_must_loop(struct page *p)
 {
 #if defined(CONFIG_HIGHMEM)
     if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) || PageHighMem(p))
         return true;
 #endif
     return false;
 }
 
 /**
  *  skb_frag_foreach_page - loop over pages in a fragment
  *
  *  @f:     skb frag to operate on
  *  @f_off:     offset from start of f->bv_page
  *  @f_len:     length from f_off to loop over
  *  @p:     (temp var) current page
  *  @p_off:     (temp var) offset from start of current page,
  *                             non-zero only on first page.
  *  @p_len:     (temp var) length in current page,
  *                 < PAGE_SIZE only on first and last page.
  *  @copied:    (temp var) length so far, excluding current p_len.
  *
  *  A fragment can hold a compound page, in which case per-page
  *  operations, notably kmap_atomic, must be called for each
  *  regular page.
  */
 #define skb_frag_foreach_page(f, f_off, f_len, p, p_off, p_len, copied) \
     for (p = skb_frag_page(f) + ((f_off) >> PAGE_SHIFT),        \
          p_off = (f_off) & (PAGE_SIZE - 1),             \
          p_len = skb_frag_must_loop(p) ?                \
          min_t(u32, f_len, PAGE_SIZE - p_off) : f_len,      \
          copied = 0;                        \
          copied < f_len;                        \
          copied += p_len, p++, p_off = 0,               \
          p_len = min_t(u32, f_len - copied, PAGE_SIZE))     \
 
 #define HAVE_HW_TIME_STAMP
 
 /**
  * struct skb_shared_hwtstamps - hardware time stamps
  * @hwtstamp:       hardware time stamp transformed into duration
  *          since arbitrary point in time
  * @netdev_data:    address/cookie of network device driver used as
  *          reference to actual hardware time stamp
  *
  * Software time stamps generated by ktime_get_real() are stored in
  * skb->tstamp.
  *
  * hwtstamps can only be compared against other hwtstamps from
  * the same device.
  *
  * This structure is attached to packets as part of the
  * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
  */
 struct skb_shared_hwtstamps {
     union {
         ktime_t hwtstamp;
         void *netdev_data;
     };
 };
 
 /* Definitions for tx_flags in struct skb_shared_info */
 enum {
     /* generate hardware time stamp */
     SKBTX_HW_TSTAMP = 1 << 0,
 
     /* generate software time stamp when queueing packet to NIC */
     SKBTX_SW_TSTAMP = 1 << 1,
 
     /* device driver is going to provide hardware time stamp */
     SKBTX_IN_PROGRESS = 1 << 2,
 
     /* generate hardware time stamp based on cycles if supported */
     SKBTX_HW_TSTAMP_USE_CYCLES = 1 << 3,
 
     /* generate wifi status information (where possible) */
     SKBTX_WIFI_STATUS = 1 << 4,
 
     /* determine hardware time stamp based on time or cycles */
     SKBTX_HW_TSTAMP_NETDEV = 1 << 5,
 
     /* generate software time stamp when entering packet scheduling */
     SKBTX_SCHED_TSTAMP = 1 << 6,
 };
 
 #define SKBTX_ANY_SW_TSTAMP (SKBTX_SW_TSTAMP    | \
                  SKBTX_SCHED_TSTAMP)
 #define SKBTX_ANY_TSTAMP    (SKBTX_HW_TSTAMP | \
                  SKBTX_HW_TSTAMP_USE_CYCLES | \
                  SKBTX_ANY_SW_TSTAMP)
 
 /* Definitions for flags in struct skb_shared_info */
 enum {
     /* use zcopy routines */
     SKBFL_ZEROCOPY_ENABLE = BIT(0),
 
     /* This indicates at least one fragment might be overwritten
      * (as in vmsplice(), sendfile() ...)
      * If we need to compute a TX checksum, we'll need to copy
      * all frags to avoid possible bad checksum
      */
     SKBFL_SHARED_FRAG = BIT(1),
 
     /* segment contains only zerocopy data and should not be
      * charged to the kernel memory.
      */
     SKBFL_PURE_ZEROCOPY = BIT(2),
 
     SKBFL_DONT_ORPHAN = BIT(3),
 
     /* page references are managed by the ubuf_info, so it's safe to
      * use frags only up until ubuf_info is released
      */
     SKBFL_MANAGED_FRAG_REFS = BIT(4),
 };
 
 #define SKBFL_ZEROCOPY_FRAG (SKBFL_ZEROCOPY_ENABLE | SKBFL_SHARED_FRAG)
 #define SKBFL_ALL_ZEROCOPY  (SKBFL_ZEROCOPY_FRAG | SKBFL_PURE_ZEROCOPY | \
                  SKBFL_DONT_ORPHAN | SKBFL_MANAGED_FRAG_REFS)
 
 /*
  * The callback notifies userspace to release buffers when skb DMA is done in
  * lower device, the skb last reference should be 0 when calling this.
  * The zerocopy_success argument is true if zero copy transmit occurred,
  * false on data copy or out of memory error caused by data copy attempt.
  * The ctx field is used to track device context.
  * The desc field is used to track userspace buffer index.
  */
 struct ubuf_info {
     void (*callback)(struct sk_buff *, struct ubuf_info *,
              bool zerocopy_success);
     union {
         struct {
             unsigned long desc;
             void *ctx;
         };
         struct {
             u32 id;
             u16 len;
             u16 zerocopy:1;
             u32 bytelen;
         };
     };
     refcount_t refcnt;
     u8 flags;
 
     struct mmpin {
         struct user_struct *user;
         unsigned int num_pg;
     } mmp;
 };
 
 #define skb_uarg(SKB)   ((struct ubuf_info *)(skb_shinfo(SKB)->destructor_arg))
 
 int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
 void mm_unaccount_pinned_pages(struct mmpin *mmp);
 
 /* This data is invariant across clones and lives at
  * the end of the header data, ie. at skb->end.
  */
 struct skb_shared_info {
     __u8        flags;
     __u8        meta_len;
     __u8        nr_frags;
     __u8        tx_flags;
     unsigned short  gso_size;
     /* Warning: this field is not always filled in (UFO)! */
     unsigned short  gso_segs;
     struct sk_buff  *frag_list;
     struct skb_shared_hwtstamps hwtstamps;
     unsigned int    gso_type;
     u32     tskey;
 
     /*
      * Warning : all fields before dataref are cleared in __alloc_skb()
      */
     atomic_t    dataref;
     unsigned int    xdp_frags_size;
 
     /* Intermediate layers must ensure that destructor_arg
      * remains valid until skb destructor */
     void *      destructor_arg;
 
     /* must be last field, see pskb_expand_head() */
     skb_frag_t  frags[MAX_SKB_FRAGS];
 };
 
 /**
  * DOC: dataref and headerless skbs
  *
  * Transport layers send out clones of payload skbs they hold for
  * retransmissions. To allow lower layers of the stack to prepend their headers
  * we split &skb_shared_info.dataref into two halves.
  * The lower 16 bits count the overall number of references.
  * The higher 16 bits indicate how many of the references are payload-only.
  * skb_header_cloned() checks if skb is allowed to add / write the headers.
  *
  * The creator of the skb (e.g. TCP) marks its skb as &sk_buff.nohdr
  * (via __skb_header_release()). Any clone created from marked skb will get
  * &sk_buff.hdr_len populated with the available headroom.
  * If there's the only clone in existence it's able to modify the headroom
  * at will. The sequence of calls inside the transport layer is::
  *
  *  <alloc skb>
  *  skb_reserve()
  *  __skb_header_release()
  *  skb_clone()
  *  // send the clone down the stack
  *
  * This is not a very generic construct and it depends on the transport layers
  * doing the right thing. In practice there's usually only one payload-only skb.
  * Having multiple payload-only skbs with different lengths of hdr_len is not
  * possible. The payload-only skbs should never leave their owner.
  */
 #define SKB_DATAREF_SHIFT 16
 #define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)
 
 
 enum {
     SKB_FCLONE_UNAVAILABLE, /* skb has no fclone (from head_cache) */
     SKB_FCLONE_ORIG,    /* orig skb (from fclone_cache) */
     SKB_FCLONE_CLONE,   /* companion fclone skb (from fclone_cache) */
 };
 
 enum {
     SKB_GSO_TCPV4 = 1 << 0,
 
     /* This indicates the skb is from an untrusted source. */
     SKB_GSO_DODGY = 1 << 1,
 
     /* This indicates the tcp segment has CWR set. */
     SKB_GSO_TCP_ECN = 1 << 2,
 
     SKB_GSO_TCP_FIXEDID = 1 << 3,
 
     SKB_GSO_TCPV6 = 1 << 4,
 
     SKB_GSO_FCOE = 1 << 5,
 
     SKB_GSO_GRE = 1 << 6,
 
     SKB_GSO_GRE_CSUM = 1 << 7,
 
     SKB_GSO_IPXIP4 = 1 << 8,
 
     SKB_GSO_IPXIP6 = 1 << 9,
 
     SKB_GSO_UDP_TUNNEL = 1 << 10,
 
     SKB_GSO_UDP_TUNNEL_CSUM = 1 << 11,
 
     SKB_GSO_PARTIAL = 1 << 12,
 
     SKB_GSO_TUNNEL_REMCSUM = 1 << 13,
 
     SKB_GSO_SCTP = 1 << 14,
 
     SKB_GSO_ESP = 1 << 15,
 
     SKB_GSO_UDP = 1 << 16,
 
     SKB_GSO_UDP_L4 = 1 << 17,
 
     SKB_GSO_FRAGLIST = 1 << 18,
 };
 
 #if BITS_PER_LONG > 32
 #define NET_SKBUFF_DATA_USES_OFFSET 1
 #endif
 
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 typedef unsigned int sk_buff_data_t;
 #else
 typedef unsigned char *sk_buff_data_t;
 #endif
 
 /**
  * DOC: Basic sk_buff geometry
  *
  * struct sk_buff itself is a metadata structure and does not hold any packet
  * data. All the data is held in associated buffers.
  *
  * &sk_buff.head points to the main "head" buffer. The head buffer is divided
  * into two parts:
  *
  *  - data buffer, containing headers and sometimes payload;
  *    this is the part of the skb operated on by the common helpers
  *    such as skb_put() or skb_pull();
  *  - shared info (struct skb_shared_info) which holds an array of pointers
  *    to read-only data in the (page, offset, length) format.
  *
  * Optionally &skb_shared_info.frag_list may point to another skb.
  *
  * Basic diagram may look like this::
  *
  *                                  ---------------
  *                                 | sk_buff       |
  *                                  ---------------
  *     ,---------------------------  + head
  *    /          ,-----------------  + data
  *   /          /      ,-----------  + tail
  *  |          |      |            , + end
  *  |          |      |           |
  *  v          v      v           v
  *   -----------------------------------------------
  *  | headroom | data |  tailroom | skb_shared_info |
  *   -----------------------------------------------
  *                                 + [page frag]
  *                                 + [page frag]
  *                                 + [page frag]
  *                                 + [page frag]       ---------
  *                                 + frag_list    --> | sk_buff |
  *                                                     ---------
  *
  */
 
 /**
  *  struct sk_buff - socket buffer
  *  @next: Next buffer in list
  *  @prev: Previous buffer in list
  *  @tstamp: Time we arrived/left
  *  @skb_mstamp_ns: (aka @tstamp) earliest departure time; start point
  *      for retransmit timer
  *  @rbnode: RB tree node, alternative to next/prev for netem/tcp
  *  @list: queue head
  *  @ll_node: anchor in an llist (eg socket defer_list)
  *  @sk: Socket we are owned by
  *  @ip_defrag_offset: (aka @sk) alternate use of @sk, used in
  *      fragmentation management
  *  @dev: Device we arrived on/are leaving by
  *  @dev_scratch: (aka @dev) alternate use of @dev when @dev would be %NULL
  *  @cb: Control buffer. Free for use by every layer. Put private vars here
  *  @_skb_refdst: destination entry (with norefcount bit)
  *  @sp: the security path, used for xfrm
  *  @len: Length of actual data
  *  @data_len: Data length
  *  @mac_len: Length of link layer header
  *  @hdr_len: writable header length of cloned skb
  *  @csum: Checksum (must include start/offset pair)
  *  @csum_start: Offset from skb->head where checksumming should start
  *  @csum_offset: Offset from csum_start where checksum should be stored
  *  @priority: Packet queueing priority
  *  @ignore_df: allow local fragmentation
  *  @cloned: Head may be cloned (check refcnt to be sure)
  *  @ip_summed: Driver fed us an IP checksum
  *  @nohdr: Payload reference only, must not modify header
  *  @pkt_type: Packet class
  *  @fclone: skbuff clone status
  *  @ipvs_property: skbuff is owned by ipvs
  *  @inner_protocol_type: whether the inner protocol is
  *      ENCAP_TYPE_ETHER or ENCAP_TYPE_IPPROTO
  *  @remcsum_offload: remote checksum offload is enabled
  *  @offload_fwd_mark: Packet was L2-forwarded in hardware
  *  @offload_l3_fwd_mark: Packet was L3-forwarded in hardware
  *  @tc_skip_classify: do not classify packet. set by IFB device
  *  @tc_at_ingress: used within tc_classify to distinguish in/egress
  *  @redirected: packet was redirected by packet classifier
  *  @from_ingress: packet was redirected from the ingress path
  *  @nf_skip_egress: packet shall skip nf egress - see netfilter_netdev.h
  *  @peeked: this packet has been seen already, so stats have been
  *      done for it, don't do them again
  *  @nf_trace: netfilter packet trace flag
  *  @protocol: Packet protocol from driver
  *  @destructor: Destruct function
  *  @tcp_tsorted_anchor: list structure for TCP (tp->tsorted_sent_queue)
  *  @_sk_redir: socket redirection information for skmsg
  *  @_nfct: Associated connection, if any (with nfctinfo bits)
  *  @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
  *  @skb_iif: ifindex of device we arrived on
  *  @tc_index: Traffic control index
  *  @hash: the packet hash
  *  @queue_mapping: Queue mapping for multiqueue devices
  *  @head_frag: skb was allocated from page fragments,
  *      not allocated by kmalloc() or vmalloc().
  *  @pfmemalloc: skbuff was allocated from PFMEMALLOC reserves
  *  @pp_recycle: mark the packet for recycling instead of freeing (implies
  *      page_pool support on driver)
  *  @active_extensions: active extensions (skb_ext_id types)
  *  @ndisc_nodetype: router type (from link layer)
  *  @ooo_okay: allow the mapping of a socket to a queue to be changed
  *  @l4_hash: indicate hash is a canonical 4-tuple hash over transport
  *      ports.
  *  @sw_hash: indicates hash was computed in software stack
  *  @wifi_acked_valid: wifi_acked was set
  *  @wifi_acked: whether frame was acked on wifi or not
  *  @no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
  *  @encapsulation: indicates the inner headers in the skbuff are valid
  *  @encap_hdr_csum: software checksum is needed
  *  @csum_valid: checksum is already valid
  *  @csum_not_inet: use CRC32c to resolve CHECKSUM_PARTIAL
  *  @csum_complete_sw: checksum was completed by software
  *  @csum_level: indicates the number of consecutive checksums found in
  *      the packet minus one that have been verified as
  *      CHECKSUM_UNNECESSARY (max 3)
  *  @dst_pending_confirm: need to confirm neighbour
  *  @decrypted: Decrypted SKB
  *  @slow_gro: state present at GRO time, slower prepare step required
  *  @mono_delivery_time: When set, skb->tstamp has the
  *      delivery_time in mono clock base (i.e. EDT).  Otherwise, the
  *      skb->tstamp has the (rcv) timestamp at ingress and
  *      delivery_time at egress.
  *  @napi_id: id of the NAPI struct this skb came from
  *  @sender_cpu: (aka @napi_id) source CPU in XPS
  *  @alloc_cpu: CPU which did the skb allocation.
  *  @secmark: security marking
  *  @mark: Generic packet mark
  *  @reserved_tailroom: (aka @mark) number of bytes of free space available
  *      at the tail of an sk_buff
  *  @vlan_present: VLAN tag is present
  *  @vlan_proto: vlan encapsulation protocol
  *  @vlan_tci: vlan tag control information
  *  @inner_protocol: Protocol (encapsulation)
  *  @inner_ipproto: (aka @inner_protocol) stores ipproto when
  *      skb->inner_protocol_type == ENCAP_TYPE_IPPROTO;
  *  @inner_transport_header: Inner transport layer header (encapsulation)
  *  @inner_network_header: Network layer header (encapsulation)
  *  @inner_mac_header: Link layer header (encapsulation)
  *  @transport_header: Transport layer header
  *  @network_header: Network layer header
  *  @mac_header: Link layer header
  *  @kcov_handle: KCOV remote handle for remote coverage collection
  *  @tail: Tail pointer
  *  @end: End pointer
  *  @head: Head of buffer
  *  @data: Data head pointer
  *  @truesize: Buffer size
  *  @users: User count - see {datagram,tcp}.c
  *  @extensions: allocated extensions, valid if active_extensions is nonzero
  */
 
 struct sk_buff {
     union {
         struct {
             /* These two members must be first to match sk_buff_head. */
             struct sk_buff      *next;
             struct sk_buff      *prev;
 
             union {
                 struct net_device   *dev;
                 /* Some protocols might use this space to store information,
                  * while device pointer would be NULL.
                  * UDP receive path is one user.
                  */
                 unsigned long       dev_scratch;
             };
         };
         struct rb_node      rbnode; /* used in netem, ip4 defrag, and tcp stack */
         struct list_head    list;
         struct llist_node   ll_node;
     };
 
     union {
         struct sock     *sk;
         int         ip_defrag_offset;
     };
 
     union {
         ktime_t     tstamp;
         u64     skb_mstamp_ns; /* earliest departure time */
     };
     /*
      * This is the control buffer. It is free to use for every
      * layer. Please put your private variables there. If you
      * want to keep them across layers you have to do a skb_clone()
      * first. This is owned by whoever has the skb queued ATM.
      */
     char            cb[48] __aligned(8);
 
     union {
         struct {
             unsigned long   _skb_refdst;
             void        (*destructor)(struct sk_buff *skb);
         };
         struct list_head    tcp_tsorted_anchor;
 #ifdef CONFIG_NET_SOCK_MSG
         unsigned long       _sk_redir;
 #endif
     };
 
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
     unsigned long        _nfct;
 #endif
     unsigned int        len,
                 data_len;
     __u16           mac_len,
                 hdr_len;
 
     /* Following fields are _not_ copied in __copy_skb_header()
      * Note that queue_mapping is here mostly to fill a hole.
      */
     __u16           queue_mapping;
 
 /* if you move cloned around you also must adapt those constants */
 #ifdef __BIG_ENDIAN_BITFIELD
 #define CLONED_MASK (1 << 7)
 #else
 #define CLONED_MASK 1
 #endif
 #define CLONED_OFFSET       offsetof(struct sk_buff, __cloned_offset)
 
     /* private: */
     __u8            __cloned_offset[0];
     /* public: */
     __u8            cloned:1,
                 nohdr:1,
                 fclone:2,
                 peeked:1,
                 head_frag:1,
                 pfmemalloc:1,
                 pp_recycle:1; /* page_pool recycle indicator */
 #ifdef CONFIG_SKB_EXTENSIONS
     __u8            active_extensions;
 #endif
 
     /* Fields enclosed in headers group are copied
      * using a single memcpy() in __copy_skb_header()
      */
     struct_group(headers,
 
     /* private: */
     __u8            __pkt_type_offset[0];
     /* public: */
     __u8            pkt_type:3; /* see PKT_TYPE_MAX */
     __u8            ignore_df:1;
     __u8            nf_trace:1;
     __u8            ip_summed:2;
     __u8            ooo_okay:1;
 
     __u8            l4_hash:1;
     __u8            sw_hash:1;
     __u8            wifi_acked_valid:1;
     __u8            wifi_acked:1;
     __u8            no_fcs:1;
     /* Indicates the inner headers are valid in the skbuff. */
     __u8            encapsulation:1;
     __u8            encap_hdr_csum:1;
     __u8            csum_valid:1;
 
     /* private: */
     __u8            __pkt_vlan_present_offset[0];
     /* public: */
     __u8            vlan_present:1; /* See PKT_VLAN_PRESENT_BIT */
     __u8            csum_complete_sw:1;
     __u8            csum_level:2;
     __u8            dst_pending_confirm:1;
     __u8            mono_delivery_time:1;   /* See SKB_MONO_DELIVERY_TIME_MASK */
 #ifdef CONFIG_NET_CLS_ACT
     __u8            tc_skip_classify:1;
     __u8            tc_at_ingress:1;    /* See TC_AT_INGRESS_MASK */
 #endif
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
     __u8            ndisc_nodetype:2;
 #endif
 
     __u8            ipvs_property:1;
     __u8            inner_protocol_type:1;
     __u8            remcsum_offload:1;
 #ifdef CONFIG_NET_SWITCHDEV
     __u8            offload_fwd_mark:1;
     __u8            offload_l3_fwd_mark:1;
 #endif
     __u8            redirected:1;
 #ifdef CONFIG_NET_REDIRECT
     __u8            from_ingress:1;
 #endif
 #ifdef CONFIG_NETFILTER_SKIP_EGRESS
     __u8            nf_skip_egress:1;
 #endif
 #ifdef CONFIG_TLS_DEVICE
     __u8            decrypted:1;
 #endif
     __u8            slow_gro:1;
     __u8            csum_not_inet:1;
 
 #ifdef CONFIG_NET_SCHED
     __u16           tc_index;   /* traffic control index */
 #endif
 
     union {
         __wsum      csum;
         struct {
             __u16   csum_start;
             __u16   csum_offset;
         };
     };
     __u32           priority;
     int         skb_iif;
     __u32           hash;
     __be16          vlan_proto;
     __u16           vlan_tci;
 #if defined(CONFIG_NET_RX_BUSY_POLL) || defined(CONFIG_XPS)
     union {
         unsigned int    napi_id;
         unsigned int    sender_cpu;
     };
 #endif
     u16         alloc_cpu;
 #ifdef CONFIG_NETWORK_SECMARK
     __u32       secmark;
 #endif
 
     union {
         __u32       mark;
         __u32       reserved_tailroom;
     };
 
     union {
         __be16      inner_protocol;
         __u8        inner_ipproto;
     };
 
     __u16           inner_transport_header;
     __u16           inner_network_header;
     __u16           inner_mac_header;
 
     __be16          protocol;
     __u16           transport_header;
     __u16           network_header;
     __u16           mac_header;
 
 #ifdef CONFIG_KCOV
     u64         kcov_handle;
 #endif
 
     ); /* end headers group */
 
     /* These elements must be at the end, see alloc_skb() for details.  */
     sk_buff_data_t      tail;
     sk_buff_data_t      end;
     unsigned char       *head,
                 *data;
     unsigned int        truesize;
     refcount_t      users;
 
 #ifdef CONFIG_SKB_EXTENSIONS
     /* only useable after checking ->active_extensions != 0 */
     struct skb_ext      *extensions;
 #endif
 };
 
 /* if you move pkt_type around you also must adapt those constants */
 #ifdef __BIG_ENDIAN_BITFIELD
 #define PKT_TYPE_MAX    (7 << 5)
 #else
 #define PKT_TYPE_MAX    7
 #endif
 #define PKT_TYPE_OFFSET     offsetof(struct sk_buff, __pkt_type_offset)
 
 /* if you move pkt_vlan_present, tc_at_ingress, or mono_delivery_time
  * around, you also must adapt these constants.
  */
 #ifdef __BIG_ENDIAN_BITFIELD
 #define PKT_VLAN_PRESENT_BIT    7
 #define TC_AT_INGRESS_MASK      (1 << 0)
 #define SKB_MONO_DELIVERY_TIME_MASK (1 << 2)
 #else
 #define PKT_VLAN_PRESENT_BIT    0
 #define TC_AT_INGRESS_MASK      (1 << 7)
 #define SKB_MONO_DELIVERY_TIME_MASK (1 << 5)
 #endif
 #define PKT_VLAN_PRESENT_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
 
 #ifdef __KERNEL__
 /*
  *  Handling routines are only of interest to the kernel
  */
 
 #define SKB_ALLOC_FCLONE    0x01
 #define SKB_ALLOC_RX        0x02
 #define SKB_ALLOC_NAPI      0x04
 
 /**
  * skb_pfmemalloc - Test if the skb was allocated from PFMEMALLOC reserves
  * @skb: buffer
  */
 static inline bool skb_pfmemalloc(const struct sk_buff *skb)
 {
     return unlikely(skb->pfmemalloc);
 }
 
 /*
  * skb might have a dst pointer attached, refcounted or not.
  * _skb_refdst low order bit is set if refcount was _not_ taken
  */
 #define SKB_DST_NOREF   1UL
 #define SKB_DST_PTRMASK ~(SKB_DST_NOREF)
 
 /**
  * skb_dst - returns skb dst_entry
  * @skb: buffer
  *
  * Returns skb dst_entry, regardless of reference taken or not.
  */
 static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
 {
     /* If refdst was not refcounted, check we still are in a
      * rcu_read_lock section
      */
     WARN_ON((skb->_skb_refdst & SKB_DST_NOREF) &&
         !rcu_read_lock_held() &&
         !rcu_read_lock_bh_held());
     return (struct dst_entry *)(skb->_skb_refdst & SKB_DST_PTRMASK);
 }
 
 /**
  * skb_dst_set - sets skb dst
  * @skb: buffer
  * @dst: dst entry
  *
  * Sets skb dst, assuming a reference was taken on dst and should
  * be released by skb_dst_drop()
  */
 static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
 {
     skb->slow_gro |= !!dst;
     skb->_skb_refdst = (unsigned long)dst;
 }
 
 /**
  * skb_dst_set_noref - sets skb dst, hopefully, without taking reference
  * @skb: buffer
  * @dst: dst entry
  *
  * Sets skb dst, assuming a reference was not taken on dst.
  * If dst entry is cached, we do not take reference and dst_release
  * will be avoided by refdst_drop. If dst entry is not cached, we take
  * reference, so that last dst_release can destroy the dst immediately.
  */
 static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
 {
     WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
     skb->slow_gro |= !!dst;
     skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
 }
 
 /**
  * skb_dst_is_noref - Test if skb dst isn't refcounted
  * @skb: buffer
  */
 static inline bool skb_dst_is_noref(const struct sk_buff *skb)
 {
     return (skb->_skb_refdst & SKB_DST_NOREF) && skb_dst(skb);
 }
 
 /**
  * skb_rtable - Returns the skb &rtable
  * @skb: buffer
  */
 static inline struct rtable *skb_rtable(const struct sk_buff *skb)
 {
     return (struct rtable *)skb_dst(skb);
 }
 
 /* For mangling skb->pkt_type from user space side from applications
  * such as nft, tc, etc, we only allow a conservative subset of
  * possible pkt_types to be set.
 */
 static inline bool skb_pkt_type_ok(u32 ptype)
 {
     return ptype <= PACKET_OTHERHOST;
 }
 
 /**
  * skb_napi_id - Returns the skb's NAPI id
  * @skb: buffer
  */
 static inline unsigned int skb_napi_id(const struct sk_buff *skb)
 {
 #ifdef CONFIG_NET_RX_BUSY_POLL
     return skb->napi_id;
 #else
     return 0;
 #endif
 }
 
 /**
  * skb_unref - decrement the skb's reference count
  * @skb: buffer
  *
  * Returns true if we can free the skb.
  */
 static inline bool skb_unref(struct sk_buff *skb)
 {
     if (unlikely(!skb))
         return false;
     if (likely(refcount_read(&skb->users) == 1))
         smp_rmb();
     else if (likely(!refcount_dec_and_test(&skb->users)))
         return false;
 
     return true;
 }
 
 void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
 
 /**
  *  kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason
  *  @skb: buffer to free
  */
 static inline void kfree_skb(struct sk_buff *skb)
 {
     kfree_skb_reason(skb, SKB_DROP_REASON_NOT_SPECIFIED);
 }
 
 void skb_release_head_state(struct sk_buff *skb);
 void kfree_skb_list_reason(struct sk_buff *segs,
                enum skb_drop_reason reason);
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
 void skb_tx_error(struct sk_buff *skb);
 
 static inline void kfree_skb_list(struct sk_buff *segs)
 {
     kfree_skb_list_reason(segs, SKB_DROP_REASON_NOT_SPECIFIED);
 }
 
 #ifdef CONFIG_TRACEPOINTS
 void consume_skb(struct sk_buff *skb);
 #else
 static inline void consume_skb(struct sk_buff *skb)
 {
     return kfree_skb(skb);
 }
 #endif
 
 void __consume_stateless_skb(struct sk_buff *skb);
 void  __kfree_skb(struct sk_buff *skb);
 extern struct kmem_cache *skbuff_head_cache;
 
 void kfree_skb_partial(struct sk_buff *skb, bool head_stolen);
 bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
               bool *fragstolen, int *delta_truesize);
 
 struct sk_buff *__alloc_skb(unsigned int size, gfp_t priority, int flags,
                 int node);
 struct sk_buff *__build_skb(void *data, unsigned int frag_size);
 struct sk_buff *build_skb(void *data, unsigned int frag_size);
 struct sk_buff *build_skb_around(struct sk_buff *skb,
                  void *data, unsigned int frag_size);
 void skb_attempt_defer_free(struct sk_buff *skb);
 
 struct sk_buff *napi_build_skb(void *data, unsigned int frag_size);
 
 /**
  * alloc_skb - allocate a network buffer
  * @size: size to allocate
  * @priority: allocation mask
  *
  * This function is a convenient wrapper around __alloc_skb().
  */
 static inline struct sk_buff *alloc_skb(unsigned int size,
                     gfp_t priority)
 {
     return __alloc_skb(size, priority, 0, NUMA_NO_NODE);
 }
 
 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);
 struct sk_buff *alloc_skb_for_msg(struct sk_buff *first);
 
 /* Layout of fast clones : [skb1][skb2][fclone_ref] */
 struct sk_buff_fclones {
     struct sk_buff  skb1;
 
     struct sk_buff  skb2;
 
     refcount_t  fclone_ref;
 };
 
 /**
  *  skb_fclone_busy - check if fclone is busy
  *  @sk: socket
  *  @skb: buffer
  *
  * Returns true if skb is a fast clone, and its clone is not freed.
  * Some drivers call skb_orphan() in their ndo_start_xmit(),
  * so we also check that this didnt happen.
  */
 static inline bool skb_fclone_busy(const struct sock *sk,
                    const struct sk_buff *skb)
 {
     const struct sk_buff_fclones *fclones;
 
     fclones = container_of(skb, struct sk_buff_fclones, skb1);
 
     return skb->fclone == SKB_FCLONE_ORIG &&
            refcount_read(&fclones->fclone_ref) > 1 &&
            READ_ONCE(fclones->skb2.sk) == sk;
 }
 
 /**
  * alloc_skb_fclone - allocate a network buffer from fclone cache
  * @size: size to allocate
  * @priority: allocation mask
  *
  * This function is a convenient wrapper around __alloc_skb().
  */
 static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
                            gfp_t priority)
 {
     return __alloc_skb(size, priority, SKB_ALLOC_FCLONE, NUMA_NO_NODE);
 }
 
 struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
 void skb_headers_offset_update(struct sk_buff *skb, int off);
 int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
 struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t priority);
 void skb_copy_header(struct sk_buff *new, const struct sk_buff *old);
 struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t priority);
 struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
                    gfp_t gfp_mask, bool fclone);
 static inline struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom,
                       gfp_t gfp_mask)
 {
     return __pskb_copy_fclone(skb, headroom, gfp_mask, false);
 }
 
 int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, gfp_t gfp_mask);
 struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
                      unsigned int headroom);
 struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom);
 struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
                 int newtailroom, gfp_t priority);
 int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
                      int offset, int len);
 int __must_check skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg,
                   int offset, int len);
 int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer);
 int __skb_pad(struct sk_buff *skb, int pad, bool free_on_error);
 
 /**
  *  skb_pad         -   zero pad the tail of an skb
  *  @skb: buffer to pad
  *  @pad: space to pad
  *
  *  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.
  */
 static inline int skb_pad(struct sk_buff *skb, int pad)
 {
     return __skb_pad(skb, pad, true);
 }
 #define dev_kfree_skb(a)    consume_skb(a)
 
 int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
              int offset, size_t size);
 
 struct skb_seq_state {
     __u32       lower_offset;
     __u32       upper_offset;
     __u32       frag_idx;
     __u32       stepped_offset;
     struct sk_buff  *root_skb;
     struct sk_buff  *cur_skb;
     __u8        *frag_data;
     __u32       frag_off;
 };
 
 void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
               unsigned int to, struct skb_seq_state *st);
 unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
               struct skb_seq_state *st);
 void skb_abort_seq_read(struct skb_seq_state *st);
 
 unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
                unsigned int to, struct ts_config *config);
 
 /*
  * Packet hash types specify the type of hash in skb_set_hash.
  *
  * Hash types refer to the protocol layer addresses which are used to
  * construct a packet's hash. The hashes are used to differentiate or identify
  * flows of the protocol layer for the hash type. Hash types are either
  * layer-2 (L2), layer-3 (L3), or layer-4 (L4).
  *
  * Properties of hashes:
  *
  * 1) Two packets in different flows have different hash values
  * 2) Two packets in the same flow should have the same hash value
  *
  * A hash at a higher layer is considered to be more specific. A driver should
  * set the most specific hash possible.
  *
  * A driver cannot indicate a more specific hash than the layer at which a hash
  * was computed. For instance an L3 hash cannot be set as an L4 hash.
  *
  * A driver may indicate a hash level which is less specific than the
  * actual layer the hash was computed on. For instance, a hash computed
  * at L4 may be considered an L3 hash. This should only be done if the
  * driver can't unambiguously determine that the HW computed the hash at
  * the higher layer. Note that the "should" in the second property above
  * permits this.
  */
 enum pkt_hash_types {
     PKT_HASH_TYPE_NONE, /* Undefined type */
     PKT_HASH_TYPE_L2,   /* Input: src_MAC, dest_MAC */
     PKT_HASH_TYPE_L3,   /* Input: src_IP, dst_IP */
     PKT_HASH_TYPE_L4,   /* Input: src_IP, dst_IP, src_port, dst_port */
 };
 
 static inline void skb_clear_hash(struct sk_buff *skb)
 {
     skb->hash = 0;
     skb->sw_hash = 0;
     skb->l4_hash = 0;
 }
 
 static inline void skb_clear_hash_if_not_l4(struct sk_buff *skb)
 {
     if (!skb->l4_hash)
         skb_clear_hash(skb);
 }
 
 static inline void
 __skb_set_hash(struct sk_buff *skb, __u32 hash, bool is_sw, bool is_l4)
 {
     skb->l4_hash = is_l4;
     skb->sw_hash = is_sw;
     skb->hash = hash;
 }
 
 static inline void
 skb_set_hash(struct sk_buff *skb, __u32 hash, enum pkt_hash_types type)
 {
     /* Used by drivers to set hash from HW */
     __skb_set_hash(skb, hash, false, type == PKT_HASH_TYPE_L4);
 }
 
 static inline void
 __skb_set_sw_hash(struct sk_buff *skb, __u32 hash, bool is_l4)
 {
     __skb_set_hash(skb, hash, true, is_l4);
 }
 
 void __skb_get_hash(struct sk_buff *skb);
 u32 __skb_get_hash_symmetric(const struct sk_buff *skb);
 u32 skb_get_poff(const struct sk_buff *skb);
 u32 __skb_get_poff(const struct sk_buff *skb, const void *data,
            const struct flow_keys_basic *keys, int hlen);
 __be32 __skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto,
                 const void *data, int hlen_proto);
 
 static inline __be32 skb_flow_get_ports(const struct sk_buff *skb,
                     int thoff, u8 ip_proto)
 {
     return __skb_flow_get_ports(skb, thoff, ip_proto, NULL, 0);
 }
 
 void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
                  const struct flow_dissector_key *key,
                  unsigned int key_count);
 
 struct bpf_flow_dissector;
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
               __be16 proto, int nhoff, int hlen, unsigned int flags);
 
 bool __skb_flow_dissect(const struct net *net,
             const struct sk_buff *skb,
             struct flow_dissector *flow_dissector,
             void *target_container, const void *data,
             __be16 proto, int nhoff, int hlen, unsigned int flags);
 
 static inline bool skb_flow_dissect(const struct sk_buff *skb,
                     struct flow_dissector *flow_dissector,
                     void *target_container, unsigned int flags)
 {
     return __skb_flow_dissect(NULL, skb, flow_dissector,
                   target_container, NULL, 0, 0, 0, flags);
 }
 
 static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
                           struct flow_keys *flow,
                           unsigned int flags)
 {
     memset(flow, 0, sizeof(*flow));
     return __skb_flow_dissect(NULL, skb, &flow_keys_dissector,
                   flow, NULL, 0, 0, 0, flags);
 }
 
 static inline bool
 skb_flow_dissect_flow_keys_basic(const struct net *net,
                  const struct sk_buff *skb,
                  struct flow_keys_basic *flow,
                  const void *data, __be16 proto,
                  int nhoff, int hlen, unsigned int flags)
 {
     memset(flow, 0, sizeof(*flow));
     return __skb_flow_dissect(net, skb, &flow_keys_basic_dissector, flow,
                   data, proto, nhoff, hlen, flags);
 }
 
 void skb_flow_dissect_meta(const struct sk_buff *skb,
                struct flow_dissector *flow_dissector,
                void *target_container);
 
 /* Gets a skb connection tracking info, ctinfo map should be a
  * map of mapsize to translate enum ip_conntrack_info states
  * to user states.
  */
 void
 skb_flow_dissect_ct(const struct sk_buff *skb,
             struct flow_dissector *flow_dissector,
             void *target_container,
             u16 *ctinfo_map, size_t mapsize,
             bool post_ct, u16 zone);
 void
 skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
                  struct flow_dissector *flow_dissector,
                  void *target_container);
 
 void skb_flow_dissect_hash(const struct sk_buff *skb,
                struct flow_dissector *flow_dissector,
                void *target_container);
 
 static inline __u32 skb_get_hash(struct sk_buff *skb)
 {
     if (!skb->l4_hash && !skb->sw_hash)
         __skb_get_hash(skb);
 
     return skb->hash;
 }
 
 static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, const struct flowi6 *fl6)
 {
     if (!skb->l4_hash && !skb->sw_hash) {
         struct flow_keys keys;
         __u32 hash = __get_hash_from_flowi6(fl6, &keys);
 
         __skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
     }
 
     return skb->hash;
 }
 
 __u32 skb_get_hash_perturb(const struct sk_buff *skb,
                const siphash_key_t *perturb);
 
 static inline __u32 skb_get_hash_raw(const struct sk_buff *skb)
 {
     return skb->hash;
 }
 
 static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from)
 {
     to->hash = from->hash;
     to->sw_hash = from->sw_hash;
     to->l4_hash = from->l4_hash;
 };
 
 static inline void skb_copy_decrypted(struct sk_buff *to,
                       const struct sk_buff *from)
 {
 #ifdef CONFIG_TLS_DEVICE
     to->decrypted = from->decrypted;
 #endif
 }
 
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 {
     return skb->head + skb->end;
 }
 
 static inline unsigned int skb_end_offset(const struct sk_buff *skb)
 {
     return skb->end;
 }
 
 static inline void skb_set_end_offset(struct sk_buff *skb, unsigned int offset)
 {
     skb->end = offset;
 }
 #else
 static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 {
     return skb->end;
 }
 
 static inline unsigned int skb_end_offset(const struct sk_buff *skb)
 {
     return skb->end - skb->head;
 }
 
 static inline void skb_set_end_offset(struct sk_buff *skb, unsigned int offset)
 {
     skb->end = skb->head + offset;
 }
 #endif
 
 struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
                        struct ubuf_info *uarg);
 
 void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
 
 void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
                bool success);
 
 int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk,
                 struct sk_buff *skb, struct iov_iter *from,
                 size_t length);
 
 static inline int skb_zerocopy_iter_dgram(struct sk_buff *skb,
                       struct msghdr *msg, int len)
 {
     return __zerocopy_sg_from_iter(msg, skb->sk, skb, &msg->msg_iter, len);
 }
 
 int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
                  struct msghdr *msg, int len,
                  struct ubuf_info *uarg);
 
 /* Internal */
 #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
 
 static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
 {
     return &skb_shinfo(skb)->hwtstamps;
 }
 
 static inline struct ubuf_info *skb_zcopy(struct sk_buff *skb)
 {
     bool is_zcopy = skb && skb_shinfo(skb)->flags & SKBFL_ZEROCOPY_ENABLE;
 
     return is_zcopy ? skb_uarg(skb) : NULL;
 }
 
 static inline bool skb_zcopy_pure(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->flags & SKBFL_PURE_ZEROCOPY;
 }
 
 static inline bool skb_zcopy_managed(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->flags & SKBFL_MANAGED_FRAG_REFS;
 }
 
 static inline bool skb_pure_zcopy_same(const struct sk_buff *skb1,
                        const struct sk_buff *skb2)
 {
     return skb_zcopy_pure(skb1) == skb_zcopy_pure(skb2);
 }
 
 static inline void net_zcopy_get(struct ubuf_info *uarg)
 {
     refcount_inc(&uarg->refcnt);
 }
 
 static inline void skb_zcopy_init(struct sk_buff *skb, struct ubuf_info *uarg)
 {
     skb_shinfo(skb)->destructor_arg = uarg;
     skb_shinfo(skb)->flags |= uarg->flags;
 }
 
 static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
                  bool *have_ref)
 {
     if (skb && uarg && !skb_zcopy(skb)) {
         if (unlikely(have_ref && *have_ref))
             *have_ref = false;
         else
             net_zcopy_get(uarg);
         skb_zcopy_init(skb, uarg);
     }
 }
 
 static inline void skb_zcopy_set_nouarg(struct sk_buff *skb, void *val)
 {
     skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t) val | 0x1UL);
     skb_shinfo(skb)->flags |= SKBFL_ZEROCOPY_FRAG;
 }
 
 static inline bool skb_zcopy_is_nouarg(struct sk_buff *skb)
 {
     return (uintptr_t) skb_shinfo(skb)->destructor_arg & 0x1UL;
 }
 
 static inline void *skb_zcopy_get_nouarg(struct sk_buff *skb)
 {
     return (void *)((uintptr_t) skb_shinfo(skb)->destructor_arg & ~0x1UL);
 }
 
 static inline void net_zcopy_put(struct ubuf_info *uarg)
 {
     if (uarg)
         uarg->callback(NULL, uarg, true);
 }
 
 static inline void net_zcopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 {
     if (uarg) {
         if (uarg->callback == msg_zerocopy_callback)
             msg_zerocopy_put_abort(uarg, have_uref);
         else if (have_uref)
             net_zcopy_put(uarg);
     }
 }
 
 /* Release a reference on a zerocopy structure */
 static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy_success)
 {
     struct ubuf_info *uarg = skb_zcopy(skb);
 
     if (uarg) {
         if (!skb_zcopy_is_nouarg(skb))
             uarg->callback(skb, uarg, zerocopy_success);
 
         skb_shinfo(skb)->flags &= ~SKBFL_ALL_ZEROCOPY;
     }
 }
 
 void __skb_zcopy_downgrade_managed(struct sk_buff *skb);
 
 static inline void skb_zcopy_downgrade_managed(struct sk_buff *skb)
 {
     if (unlikely(skb_zcopy_managed(skb)))
         __skb_zcopy_downgrade_managed(skb);
 }
 
 static inline void skb_mark_not_on_list(struct sk_buff *skb)
 {
     skb->next = NULL;
 }
 
 /* Iterate through singly-linked GSO fragments of an skb. */
 #define skb_list_walk_safe(first, skb, next_skb)                               \
     for ((skb) = (first), (next_skb) = (skb) ? (skb)->next : NULL; (skb);  \
          (skb) = (next_skb), (next_skb) = (skb) ? (skb)->next : NULL)
 
 static inline void skb_list_del_init(struct sk_buff *skb)
 {
     __list_del_entry(&skb->list);
     skb_mark_not_on_list(skb);
 }
 
 /**
  *  skb_queue_empty - check if a queue is empty
  *  @list: queue head
  *
  *  Returns true if the queue is empty, false otherwise.
  */
 static inline int skb_queue_empty(const struct sk_buff_head *list)
 {
     return list->next == (const struct sk_buff *) list;
 }
 
 /**
  *  skb_queue_empty_lockless - check if a queue is empty
  *  @list: queue head
  *
  *  Returns true if the queue is empty, false otherwise.
  *  This variant can be used in lockless contexts.
  */
 static inline bool skb_queue_empty_lockless(const struct sk_buff_head *list)
 {
     return READ_ONCE(list->next) == (const struct sk_buff *) list;
 }
 
 
 /**
  *  skb_queue_is_last - check if skb is the last entry in the queue
  *  @list: queue head
  *  @skb: buffer
  *
  *  Returns true if @skb is the last buffer on the list.
  */
 static inline bool skb_queue_is_last(const struct sk_buff_head *list,
                      const struct sk_buff *skb)
 {
     return skb->next == (const struct sk_buff *) list;
 }
 
 /**
  *  skb_queue_is_first - check if skb is the first entry in the queue
  *  @list: queue head
  *  @skb: buffer
  *
  *  Returns true if @skb is the first buffer on the list.
  */
 static inline bool skb_queue_is_first(const struct sk_buff_head *list,
                       const struct sk_buff *skb)
 {
     return skb->prev == (const struct sk_buff *) list;
 }
 
 /**
  *  skb_queue_next - return the next packet in the queue
  *  @list: queue head
  *  @skb: current buffer
  *
  *  Return the next packet in @list after @skb.  It is only valid to
  *  call this if skb_queue_is_last() evaluates to false.
  */
 static inline struct sk_buff *skb_queue_next(const struct sk_buff_head *list,
                          const struct sk_buff *skb)
 {
     /* This BUG_ON may seem severe, but if we just return then we
      * are going to dereference garbage.
      */
     BUG_ON(skb_queue_is_last(list, skb));
     return skb->next;
 }
 
 /**
  *  skb_queue_prev - return the prev packet in the queue
  *  @list: queue head
  *  @skb: current buffer
  *
  *  Return the prev packet in @list before @skb.  It is only valid to
  *  call this if skb_queue_is_first() evaluates to false.
  */
 static inline struct sk_buff *skb_queue_prev(const struct sk_buff_head *list,
                          const struct sk_buff *skb)
 {
     /* This BUG_ON may seem severe, but if we just return then we
      * are going to dereference garbage.
      */
     BUG_ON(skb_queue_is_first(list, skb));
     return skb->prev;
 }
 
 /**
  *  skb_get - reference buffer
  *  @skb: buffer to reference
  *
  *  Makes another reference to a socket buffer and returns a pointer
  *  to the buffer.
  */
 static inline struct sk_buff *skb_get(struct sk_buff *skb)
 {
     refcount_inc(&skb->users);
     return skb;
 }
 
 /*
  * If users == 1, we are the only owner and can avoid redundant atomic changes.
  */
 
 /**
  *  skb_cloned - is the buffer a clone
  *  @skb: buffer to check
  *
  *  Returns true if the buffer was generated with skb_clone() and is
  *  one of multiple shared copies of the buffer. Cloned buffers are
  *  shared data so must not be written to under normal circumstances.
  */
 static inline int skb_cloned(const struct sk_buff *skb)
 {
     return skb->cloned &&
            (atomic_read(&skb_shinfo(skb)->dataref) & SKB_DATAREF_MASK) != 1;
 }
 
 static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
 {
     might_sleep_if(gfpflags_allow_blocking(pri));
 
     if (skb_cloned(skb))
         return pskb_expand_head(skb, 0, 0, pri);
 
     return 0;
 }
 
 /* This variant of skb_unclone() makes sure skb->truesize
  * and skb_end_offset() are not changed, whenever a new skb->head is needed.
  *
  * Indeed there is no guarantee that ksize(kmalloc(X)) == ksize(kmalloc(X))
  * when various debugging features are in place.
  */
 int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri);
 static inline int skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
 {
     might_sleep_if(gfpflags_allow_blocking(pri));
 
     if (skb_cloned(skb))
         return __skb_unclone_keeptruesize(skb, pri);
     return 0;
 }
 
 /**
  *  skb_header_cloned - is the header a clone
  *  @skb: buffer to check
  *
  *  Returns true if modifying the header part of the buffer requires
  *  the data to be copied.
  */
 static inline int skb_header_cloned(const struct sk_buff *skb)
 {
     int dataref;
 
     if (!skb->cloned)
         return 0;
 
     dataref = atomic_read(&skb_shinfo(skb)->dataref);
     dataref = (dataref & SKB_DATAREF_MASK) - (dataref >> SKB_DATAREF_SHIFT);
     return dataref != 1;
 }
 
 static inline int skb_header_unclone(struct sk_buff *skb, gfp_t pri)
 {
     might_sleep_if(gfpflags_allow_blocking(pri));
 
     if (skb_header_cloned(skb))
         return pskb_expand_head(skb, 0, 0, pri);
 
     return 0;
 }
 
 /**
  * __skb_header_release() - allow clones to use the headroom
  * @skb: buffer to operate on
  *
  * See "DOC: dataref and headerless skbs".
  */
 static inline void __skb_header_release(struct sk_buff *skb)
 {
     skb->nohdr = 1;
     atomic_set(&skb_shinfo(skb)->dataref, 1 + (1 << SKB_DATAREF_SHIFT));
 }
 
 
 /**
  *  skb_shared - is the buffer shared
  *  @skb: buffer to check
  *
  *  Returns true if more than one person has a reference to this
  *  buffer.
  */
 static inline int skb_shared(const struct sk_buff *skb)
 {
     return refcount_read(&skb->users) != 1;
 }
 
 /**
  *  skb_share_check - check if buffer is shared and if so clone it
  *  @skb: buffer to check
  *  @pri: priority for memory allocation
  *
  *  If the buffer is shared the buffer is cloned and the old copy
  *  drops a reference. A new clone with a single reference is returned.
  *  If the buffer is not shared the original buffer is returned. When
  *  being called from interrupt status or with spinlocks held pri must
  *  be GFP_ATOMIC.
  *
  *  NULL is returned on a memory allocation failure.
  */
 static inline struct sk_buff *skb_share_check(struct sk_buff *skb, gfp_t pri)
 {
     might_sleep_if(gfpflags_allow_blocking(pri));
     if (skb_shared(skb)) {
         struct sk_buff *nskb = skb_clone(skb, pri);
 
         if (likely(nskb))
             consume_skb(skb);
         else
             kfree_skb(skb);
         skb = nskb;
     }
     return skb;
 }
 
 /*
  *  Copy shared buffers into a new sk_buff. We effectively do COW on
  *  packets to handle cases where we have a local reader and forward
  *  and a couple of other messy ones. The normal one is tcpdumping
  *  a packet thats being forwarded.
  */
 
 /**
  *  skb_unshare - make a copy of a shared buffer
  *  @skb: buffer to check
  *  @pri: priority for memory allocation
  *
  *  If the socket buffer is a clone then this function creates a new
  *  copy of the data, drops a reference count on the old copy and returns
  *  the new copy with the reference count at 1. If the buffer is not a clone
  *  the original buffer is returned. When called with a spinlock held or
  *  from interrupt state @pri must be %GFP_ATOMIC
  *
  *  %NULL is returned on a memory allocation failure.
  */
 static inline struct sk_buff *skb_unshare(struct sk_buff *skb,
                       gfp_t pri)
 {
     might_sleep_if(gfpflags_allow_blocking(pri));
     if (skb_cloned(skb)) {
         struct sk_buff *nskb = skb_copy(skb, pri);
 
         /* Free our shared copy */
         if (likely(nskb))
             consume_skb(skb);
         else
             kfree_skb(skb);
         skb = nskb;
     }
     return skb;
 }
 
 /**
  *  skb_peek - peek at the head of an &sk_buff_head
  *  @list_: list to peek at
  *
  *  Peek an &sk_buff. Unlike most other operations you _MUST_
  *  be careful with this one. A peek leaves the buffer on the
  *  list and someone else may run off with it. You must hold
  *  the appropriate locks or have a private queue to do this.
  *
  *  Returns %NULL for an empty list or a pointer to the head element.
  *  The reference count is not incremented and the reference is therefore
  *  volatile. Use with caution.
  */
 static inline struct sk_buff *skb_peek(const struct sk_buff_head *list_)
 {
     struct sk_buff *skb = list_->next;
 
     if (skb == (struct sk_buff *)list_)
         skb = NULL;
     return skb;
 }
 
 /**
  *  __skb_peek - peek at the head of a non-empty &sk_buff_head
  *  @list_: list to peek at
  *
  *  Like skb_peek(), but the caller knows that the list is not empty.
  */
 static inline struct sk_buff *__skb_peek(const struct sk_buff_head *list_)
 {
     return list_->next;
 }
 
 /**
  *  skb_peek_next - peek skb following the given one from a queue
  *  @skb: skb to start from
  *  @list_: list to peek at
  *
  *  Returns %NULL when the end of the list is met or a pointer to the
  *  next element. The reference count is not incremented and the
  *  reference is therefore volatile. Use with caution.
  */
 static inline struct sk_buff *skb_peek_next(struct sk_buff *skb,
         const struct sk_buff_head *list_)
 {
     struct sk_buff *next = skb->next;
 
     if (next == (struct sk_buff *)list_)
         next = NULL;
     return next;
 }
 
 /**
  *  skb_peek_tail - peek at the tail of an &sk_buff_head
  *  @list_: list to peek at
  *
  *  Peek an &sk_buff. Unlike most other operations you _MUST_
  *  be careful with this one. A peek leaves the buffer on the
  *  list and someone else may run off with it. You must hold
  *  the appropriate locks or have a private queue to do this.
  *
  *  Returns %NULL for an empty list or a pointer to the tail element.
  *  The reference count is not incremented and the reference is therefore
  *  volatile. Use with caution.
  */
 static inline struct sk_buff *skb_peek_tail(const struct sk_buff_head *list_)
 {
     struct sk_buff *skb = READ_ONCE(list_->prev);
 
     if (skb == (struct sk_buff *)list_)
         skb = NULL;
     return skb;
 
 }
 
 /**
  *  skb_queue_len   - get queue length
  *  @list_: list to measure
  *
  *  Return the length of an &sk_buff queue.
  */
 static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
 {
     return list_->qlen;
 }
 
 /**
  *  skb_queue_len_lockless  - get queue length
  *  @list_: list to measure
  *
  *  Return the length of an &sk_buff queue.
  *  This variant can be used in lockless contexts.
  */
 static inline __u32 skb_queue_len_lockless(const struct sk_buff_head *list_)
 {
     return READ_ONCE(list_->qlen);
 }
 
 /**
  *  __skb_queue_head_init - initialize non-spinlock portions of sk_buff_head
  *  @list: queue to initialize
  *
  *  This initializes only the list and queue length aspects of
  *  an sk_buff_head object.  This allows to initialize the list
  *  aspects of an sk_buff_head without reinitializing things like
  *  the spinlock.  It can also be used for on-stack sk_buff_head
  *  objects where the spinlock is known to not be used.
  */
 static inline void __skb_queue_head_init(struct sk_buff_head *list)
 {
     list->prev = list->next = (struct sk_buff *)list;
     list->qlen = 0;
 }
 
 /*
  * This function creates a split out lock class for each invocation;
  * this is needed for now since a whole lot of users of the skb-queue
  * infrastructure in drivers have different locking usage (in hardirq)
  * than the networking core (in softirq only). In the long run either the
  * network layer or drivers should need annotation to consolidate the
  * main types of usage into 3 classes.
  */
 static inline void skb_queue_head_init(struct sk_buff_head *list)
 {
     spin_lock_init(&list->lock);
     __skb_queue_head_init(list);
 }
 
 static inline void skb_queue_head_init_class(struct sk_buff_head *list,
         struct lock_class_key *class)
 {
     skb_queue_head_init(list);
     lockdep_set_class(&list->lock, class);
 }
 
 /*
  *  Insert an sk_buff on a list.
  *
  *  The "__skb_xxxx()" functions are the non-atomic ones that
  *  can only be called with interrupts disabled.
  */
 static inline void __skb_insert(struct sk_buff *newsk,
                 struct sk_buff *prev, struct sk_buff *next,
                 struct sk_buff_head *list)
 {
     /* See skb_queue_empty_lockless() and skb_peek_tail()
      * for the opposite READ_ONCE()
      */
     WRITE_ONCE(newsk->next, next);
     WRITE_ONCE(newsk->prev, prev);
     WRITE_ONCE(((struct sk_buff_list *)next)->prev, newsk);
     WRITE_ONCE(((struct sk_buff_list *)prev)->next, newsk);
     WRITE_ONCE(list->qlen, list->qlen + 1);
 }
 
 static inline void __skb_queue_splice(const struct sk_buff_head *list,
                       struct sk_buff *prev,
                       struct sk_buff *next)
 {
     struct sk_buff *first = list->next;
     struct sk_buff *last = list->prev;
 
     WRITE_ONCE(first->prev, prev);
     WRITE_ONCE(prev->next, first);
 
     WRITE_ONCE(last->next, next);
     WRITE_ONCE(next->prev, last);
 }
 
 /**
  *  skb_queue_splice - join two skb lists, this is designed for stacks
  *  @list: the new list to add
  *  @head: the place to add it in the first list
  */
 static inline void skb_queue_splice(const struct sk_buff_head *list,
                     struct sk_buff_head *head)
 {
     if (!skb_queue_empty(list)) {
         __skb_queue_splice(list, (struct sk_buff *) head, head->next);
         head->qlen += list->qlen;
     }
 }
 
 /**
  *  skb_queue_splice_init - join two skb lists and reinitialise the emptied list
  *  @list: the new list to add
  *  @head: the place to add it in the first list
  *
  *  The list at @list is reinitialised
  */
 static inline void skb_queue_splice_init(struct sk_buff_head *list,
                      struct sk_buff_head *head)
 {
     if (!skb_queue_empty(list)) {
         __skb_queue_splice(list, (struct sk_buff *) head, head->next);
         head->qlen += list->qlen;
         __skb_queue_head_init(list);
     }
 }
 
 /**
  *  skb_queue_splice_tail - join two skb lists, each list being a queue
  *  @list: the new list to add
  *  @head: the place to add it in the first list
  */
 static inline void skb_queue_splice_tail(const struct sk_buff_head *list,
                      struct sk_buff_head *head)
 {
     if (!skb_queue_empty(list)) {
         __skb_queue_splice(list, head->prev, (struct sk_buff *) head);
         head->qlen += list->qlen;
     }
 }
 
 /**
  *  skb_queue_splice_tail_init - join two skb lists and reinitialise the emptied list
  *  @list: the new list to add
  *  @head: the place to add it in the first list
  *
  *  Each of the lists is a queue.
  *  The list at @list is reinitialised
  */
 static inline void skb_queue_splice_tail_init(struct sk_buff_head *list,
                           struct sk_buff_head *head)
 {
     if (!skb_queue_empty(list)) {
         __skb_queue_splice(list, head->prev, (struct sk_buff *) head);
         head->qlen += list->qlen;
         __skb_queue_head_init(list);
     }
 }
 
 /**
  *  __skb_queue_after - queue a buffer at the list head
  *  @list: list to use
  *  @prev: place after this buffer
  *  @newsk: buffer to queue
  *
  *  Queue a buffer int the middle of a list. This function takes no locks
  *  and you must therefore hold required locks before calling it.
  *
  *  A buffer cannot be placed on two lists at the same time.
  */
 static inline void __skb_queue_after(struct sk_buff_head *list,
                      struct sk_buff *prev,
                      struct sk_buff *newsk)
 {
     __skb_insert(newsk, prev, ((struct sk_buff_list *)prev)->next, list);
 }
 
 void skb_append(struct sk_buff *old, struct sk_buff *newsk,
         struct sk_buff_head *list);
 
 static inline void __skb_queue_before(struct sk_buff_head *list,
                       struct sk_buff *next,
                       struct sk_buff *newsk)
 {
     __skb_insert(newsk, ((struct sk_buff_list *)next)->prev, next, list);
 }
 
 /**
  *  __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 a list. This function takes no locks
  *  and you must therefore hold required locks before calling it.
  *
  *  A buffer cannot be placed on two lists at the same time.
  */
 static inline void __skb_queue_head(struct sk_buff_head *list,
                     struct sk_buff *newsk)
 {
     __skb_queue_after(list, (struct sk_buff *)list, newsk);
 }
 void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk);
 
 /**
  *  __skb_queue_tail - queue a buffer at the list tail
  *  @list: list to use
  *  @newsk: buffer to queue
  *
  *  Queue a buffer at the end of a list. This function takes no locks
  *  and you must therefore hold required locks before calling it.
  *
  *  A buffer cannot be placed on two lists at the same time.
  */
 static inline void __skb_queue_tail(struct sk_buff_head *list,
                    struct sk_buff *newsk)
 {
     __skb_queue_before(list, (struct sk_buff *)list, newsk);
 }
 void skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk);
 
 /*
  * remove sk_buff from list. _Must_ be called atomically, and with
  * the list known..
  */
 void skb_unlink(struct sk_buff *skb, struct sk_buff_head *list);
 static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
 {
     struct sk_buff *next, *prev;
 
     WRITE_ONCE(list->qlen, list->qlen - 1);
     next       = skb->next;
     prev       = skb->prev;
     skb->next  = skb->prev = NULL;
     WRITE_ONCE(next->prev, prev);
     WRITE_ONCE(prev->next, next);
 }
 
 /**
  *  __skb_dequeue - remove from the head of the queue
  *  @list: list to dequeue from
  *
  *  Remove the head of the list. This function does not take any locks
  *  so must be used with appropriate locks held only. The head item is
  *  returned or %NULL if the list is empty.
  */
 static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list)
 {
     struct sk_buff *skb = skb_peek(list);
     if (skb)
         __skb_unlink(skb, list);
     return skb;
 }
 struct sk_buff *skb_dequeue(struct sk_buff_head *list);
 
 /**
  *  __skb_dequeue_tail - remove from the tail of the queue
  *  @list: list to dequeue from
  *
  *  Remove the tail of the list. This function does not take any locks
  *  so must be used with appropriate locks held only. The tail item is
  *  returned or %NULL if the list is empty.
  */
 static inline struct sk_buff *__skb_dequeue_tail(struct sk_buff_head *list)
 {
     struct sk_buff *skb = skb_peek_tail(list);
     if (skb)
         __skb_unlink(skb, list);
     return skb;
 }
 struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list);
 
 
 static inline bool skb_is_nonlinear(const struct sk_buff *skb)
 {
     return skb->data_len;
 }
 
 static inline unsigned int skb_headlen(const struct sk_buff *skb)
 {
     return skb->len - skb->data_len;
 }
 
 static inline unsigned int __skb_pagelen(const struct sk_buff *skb)
 {
     unsigned int i, len = 0;
 
     for (i = skb_shinfo(skb)->nr_frags - 1; (int)i >= 0; i--)
         len += skb_frag_size(&skb_shinfo(skb)->frags[i]);
     return len;
 }
 
 static inline unsigned int skb_pagelen(const struct sk_buff *skb)
 {
     return skb_headlen(skb) + __skb_pagelen(skb);
 }
 
 static inline void __skb_fill_page_desc_noacc(struct skb_shared_info *shinfo,
                           int i, struct page *page,
                           int off, int size)
 {
     skb_frag_t *frag = &shinfo->frags[i];
 
     /*
      * Propagate page pfmemalloc to the skb if we can. The problem is
      * that not all callers have unique ownership of the page but rely
      * on page_is_pfmemalloc doing the right thing(tm).
      */
     frag->bv_page         = page;
     frag->bv_offset       = off;
     skb_frag_size_set(frag, size);
 }
 
 /**
  * skb_len_add - adds a number to len fields of skb
  * @skb: buffer to add len to
  * @delta: number of bytes to add
  */
 static inline void skb_len_add(struct sk_buff *skb, int delta)
 {
     skb->len += delta;
     skb->data_len += delta;
     skb->truesize += delta;
 }
 
 /**
  * __skb_fill_page_desc - initialise a paged fragment in an skb
  * @skb: buffer containing fragment to be initialised
  * @i: paged fragment index to initialise
  * @page: the page to use for this fragment
  * @off: the offset to the data with @page
  * @size: the length of the data
  *
  * Initialises the @i'th fragment of @skb to point to &size bytes at
  * offset @off within @page.
  *
  * Does not take any additional reference on the fragment.
  */
 static inline void __skb_fill_page_desc(struct sk_buff *skb, int i,
                     struct page *page, int off, int size)
 {
     __skb_fill_page_desc_noacc(skb_shinfo(skb), i, page, off, size);
     page = compound_head(page);
     if (page_is_pfmemalloc(page))
         skb->pfmemalloc = true;
 }
 
 /**
  * skb_fill_page_desc - initialise a paged fragment in an skb
  * @skb: buffer containing fragment to be initialised
  * @i: paged fragment index to initialise
  * @page: the page to use for this fragment
  * @off: the offset to the data with @page
  * @size: the length of the data
  *
  * As per __skb_fill_page_desc() -- initialises the @i'th fragment of
  * @skb to point to @size bytes at offset @off within @page. In
  * addition updates @skb such that @i is the last fragment.
  *
  * Does not take any additional reference on the fragment.
  */
 static inline void skb_fill_page_desc(struct sk_buff *skb, int i,
                       struct page *page, int off, int size)
 {
     __skb_fill_page_desc(skb, i, page, off, size);
     skb_shinfo(skb)->nr_frags = i + 1;
 }
 
 /**
  * skb_fill_page_desc_noacc - initialise a paged fragment in an skb
  * @skb: buffer containing fragment to be initialised
  * @i: paged fragment index to initialise
  * @page: the page to use for this fragment
  * @off: the offset to the data with @page
  * @size: the length of the data
  *
  * Variant of skb_fill_page_desc() which does not deal with
  * pfmemalloc, if page is not owned by us.
  */
 static inline void skb_fill_page_desc_noacc(struct sk_buff *skb, int i,
                         struct page *page, int off,
                         int size)
 {
     struct skb_shared_info *shinfo = skb_shinfo(skb);
 
     __skb_fill_page_desc_noacc(shinfo, i, page, off, size);
     shinfo->nr_frags = i + 1;
 }
 
 void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
              int size, unsigned int truesize);
 
 void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
               unsigned int truesize);
 
 #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
 
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
 {
     return skb->head + skb->tail;
 }
 
 static inline void skb_reset_tail_pointer(struct sk_buff *skb)
 {
     skb->tail = skb->data - skb->head;
 }
 
 static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 {
     skb_reset_tail_pointer(skb);
     skb->tail += offset;
 }
 
 #else /* NET_SKBUFF_DATA_USES_OFFSET */
 static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
 {
     return skb->tail;
 }
 
 static inline void skb_reset_tail_pointer(struct sk_buff *skb)
 {
     skb->tail = skb->data;
 }
 
 static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 {
     skb->tail = skb->data + offset;
 }
 
 #endif /* NET_SKBUFF_DATA_USES_OFFSET */
 
 static inline void skb_assert_len(struct sk_buff *skb)
 {
 #ifdef CONFIG_DEBUG_NET
     if (WARN_ONCE(!skb->len, "%s\n", __func__))
         DO_ONCE_LITE(skb_dump, KERN_ERR, skb, false);
 #endif /* CONFIG_DEBUG_NET */
 }
 
 /*
  *  Add data to an sk_buff
  */
 void *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len);
 void *skb_put(struct sk_buff *skb, unsigned int len);
 static inline 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;
     return tmp;
 }
 
 static inline void *__skb_put_zero(struct sk_buff *skb, unsigned int len)
 {
     void *tmp = __skb_put(skb, len);
 
     memset(tmp, 0, len);
     return tmp;
 }
 
 static inline void *__skb_put_data(struct sk_buff *skb, const void *data,
                    unsigned int len)
 {
     void *tmp = __skb_put(skb, len);
 
     memcpy(tmp, data, len);
     return tmp;
 }
 
 static inline void __skb_put_u8(struct sk_buff *skb, u8 val)
 {
     *(u8 *)__skb_put(skb, 1) = val;
 }
 
 static inline void *skb_put_zero(struct sk_buff *skb, unsigned int len)
 {
     void *tmp = skb_put(skb, len);
 
     memset(tmp, 0, len);
 
     return tmp;
 }
 
 static inline void *skb_put_data(struct sk_buff *skb, const void *data,
                  unsigned int len)
 {
     void *tmp = skb_put(skb, len);
 
     memcpy(tmp, data, len);
 
     return tmp;
 }
 
 static inline void skb_put_u8(struct sk_buff *skb, u8 val)
 {
     *(u8 *)skb_put(skb, 1) = val;
 }
 
 void *skb_push(struct sk_buff *skb, unsigned int len);
 static inline void *__skb_push(struct sk_buff *skb, unsigned int len)
 {
     skb->data -= len;
     skb->len  += len;
     return skb->data;
 }
 
 void *skb_pull(struct sk_buff *skb, unsigned int len);
 static inline void *__skb_pull(struct sk_buff *skb, unsigned int len)
 {
     skb->len -= len;
     if (unlikely(skb->len < skb->data_len)) {
 #if defined(CONFIG_DEBUG_NET)
         skb->len += len;
         pr_err("__skb_pull(len=%u)\n", len);
         skb_dump(KERN_ERR, skb, false);
 #endif
         BUG();
     }
     return skb->data += len;
 }
 
 static inline void *skb_pull_inline(struct sk_buff *skb, unsigned int len)
 {
     return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
 }
 
 void *skb_pull_data(struct sk_buff *skb, size_t len);
 
 void *__pskb_pull_tail(struct sk_buff *skb, int delta);
 
 static inline void *__pskb_pull(struct sk_buff *skb, unsigned int len)
 {
     if (len > skb_headlen(skb) &&
         !__pskb_pull_tail(skb, len - skb_headlen(skb)))
         return NULL;
     skb->len -= len;
     return skb->data += len;
 }
 
 static inline void *pskb_pull(struct sk_buff *skb, unsigned int len)
 {
     return unlikely(len > skb->len) ? NULL : __pskb_pull(skb, len);
 }
 
 static inline bool pskb_may_pull(struct sk_buff *skb, unsigned int len)
 {
     if (likely(len <= skb_headlen(skb)))
         return true;
     if (unlikely(len > skb->len))
         return false;
     return __pskb_pull_tail(skb, len - skb_headlen(skb)) != NULL;
 }
 
 void skb_condense(struct sk_buff *skb);
 
 /**
  *  skb_headroom - bytes at buffer head
  *  @skb: buffer to check
  *
  *  Return the number of bytes of free space at the head of an &sk_buff.
  */
 static inline unsigned int skb_headroom(const struct sk_buff *skb)
 {
     return skb->data - skb->head;
 }
 
 /**
  *  skb_tailroom - bytes at buffer end
  *  @skb: buffer to check
  *
  *  Return the number of bytes of free space at the tail of an sk_buff
  */
 static inline int skb_tailroom(const struct sk_buff *skb)
 {
     return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
 }
 
 /**
  *  skb_availroom - bytes at buffer end
  *  @skb: buffer to check
  *
  *  Return the number of bytes of free space at the tail of an sk_buff
  *  allocated by sk_stream_alloc()
  */
 static inline int skb_availroom(const struct sk_buff *skb)
 {
     if (skb_is_nonlinear(skb))
         return 0;
 
     return skb->end - skb->tail - skb->reserved_tailroom;
 }
 
 /**
  *  skb_reserve - adjust headroom
  *  @skb: buffer to alter
  *  @len: bytes to move
  *
  *  Increase the headroom of an empty &sk_buff by reducing the tail
  *  room. This is only allowed for an empty buffer.
  */
 static inline void skb_reserve(struct sk_buff *skb, int len)
 {
     skb->data += len;
     skb->tail += len;
 }
 
 /**
  *  skb_tailroom_reserve - adjust reserved_tailroom
  *  @skb: buffer to alter
  *  @mtu: maximum amount of headlen permitted
  *  @needed_tailroom: minimum amount of reserved_tailroom
  *
  *  Set reserved_tailroom so that headlen can be as large as possible but
  *  not larger than mtu and tailroom cannot be smaller than
  *  needed_tailroom.
  *  The required headroom should already have been reserved before using
  *  this function.
  */
 static inline void skb_tailroom_reserve(struct sk_buff *skb, unsigned int mtu,
                     unsigned int needed_tailroom)
 {
     SKB_LINEAR_ASSERT(skb);
     if (mtu < skb_tailroom(skb) - needed_tailroom)
         /* use at most mtu */
         skb->reserved_tailroom = skb_tailroom(skb) - mtu;
     else
         /* use up to all available space */
         skb->reserved_tailroom = needed_tailroom;
 }
 
 #define ENCAP_TYPE_ETHER    0
 #define ENCAP_TYPE_IPPROTO  1
 
 static inline void skb_set_inner_protocol(struct sk_buff *skb,
                       __be16 protocol)
 {
     skb->inner_protocol = protocol;
     skb->inner_protocol_type = ENCAP_TYPE_ETHER;
 }
 
 static inline void skb_set_inner_ipproto(struct sk_buff *skb,
                      __u8 ipproto)
 {
     skb->inner_ipproto = ipproto;
     skb->inner_protocol_type = ENCAP_TYPE_IPPROTO;
 }
 
 static inline void skb_reset_inner_headers(struct sk_buff *skb)
 {
     skb->inner_mac_header = skb->mac_header;
     skb->inner_network_header = skb->network_header;
     skb->inner_transport_header = skb->transport_header;
 }
 
 static inline void skb_reset_mac_len(struct sk_buff *skb)
 {
     skb->mac_len = skb->network_header - skb->mac_header;
 }
 
 static inline unsigned char *skb_inner_transport_header(const struct sk_buff
                             *skb)
 {
     return skb->head + skb->inner_transport_header;
 }
 
 static inline int skb_inner_transport_offset(const struct sk_buff *skb)
 {
     return skb_inner_transport_header(skb) - skb->data;
 }
 
 static inline void skb_reset_inner_transport_header(struct sk_buff *skb)
 {
     skb->inner_transport_header = skb->data - skb->head;
 }
 
 static inline void skb_set_inner_transport_header(struct sk_buff *skb,
                            const int offset)
 {
     skb_reset_inner_transport_header(skb);
     skb->inner_transport_header += offset;
 }
 
 static inline unsigned char *skb_inner_network_header(const struct sk_buff *skb)
 {
     return skb->head + skb->inner_network_header;
 }
 
 static inline void skb_reset_inner_network_header(struct sk_buff *skb)
 {
     skb->inner_network_header = skb->data - skb->head;
 }
 
 static inline void skb_set_inner_network_header(struct sk_buff *skb,
                         const int offset)
 {
     skb_reset_inner_network_header(skb);
     skb->inner_network_header += offset;
 }
 
 static inline unsigned char *skb_inner_mac_header(const struct sk_buff *skb)
 {
     return skb->head + skb->inner_mac_header;
 }
 
 static inline void skb_reset_inner_mac_header(struct sk_buff *skb)
 {
     skb->inner_mac_header = skb->data - skb->head;
 }
 
 static inline void skb_set_inner_mac_header(struct sk_buff *skb,
                         const int offset)
 {
     skb_reset_inner_mac_header(skb);
     skb->inner_mac_header += offset;
 }
 static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
 {
     return skb->transport_header != (typeof(skb->transport_header))~0U;
 }
 
 static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
 {
     DEBUG_NET_WARN_ON_ONCE(!skb_transport_header_was_set(skb));
     return skb->head + skb->transport_header;
 }
 
 static inline void skb_reset_transport_header(struct sk_buff *skb)
 {
     skb->transport_header = skb->data - skb->head;
 }
 
 static inline void skb_set_transport_header(struct sk_buff *skb,
                         const int offset)
 {
     skb_reset_transport_header(skb);
     skb->transport_header += offset;
 }
 
 static inline unsigned char *skb_network_header(const struct sk_buff *skb)
 {
     return skb->head + skb->network_header;
 }
 
 static inline void skb_reset_network_header(struct sk_buff *skb)
 {
     skb->network_header = skb->data - skb->head;
 }
 
 static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
 {
     skb_reset_network_header(skb);
     skb->network_header += offset;
 }
 
 static inline int skb_mac_header_was_set(const struct sk_buff *skb)
 {
     return skb->mac_header != (typeof(skb->mac_header))~0U;
 }
 
 static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
 {
     DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
     return skb->head + skb->mac_header;
 }
 
 static inline int skb_mac_offset(const struct sk_buff *skb)
 {
     return skb_mac_header(skb) - skb->data;
 }
 
 static inline u32 skb_mac_header_len(const struct sk_buff *skb)
 {
     DEBUG_NET_WARN_ON_ONCE(!skb_mac_header_was_set(skb));
     return skb->network_header - skb->mac_header;
 }
 
 static inline void skb_unset_mac_header(struct sk_buff *skb)
 {
     skb->mac_header = (typeof(skb->mac_header))~0U;
 }
 
 static inline void skb_reset_mac_header(struct sk_buff *skb)
 {
     skb->mac_header = skb->data - skb->head;
 }
 
 static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
 {
     skb_reset_mac_header(skb);
     skb->mac_header += offset;
 }
 
 static inline void skb_pop_mac_header(struct sk_buff *skb)
 {
     skb->mac_header = skb->network_header;
 }
 
 static inline void skb_probe_transport_header(struct sk_buff *skb)
 {
     struct flow_keys_basic keys;
 
     if (skb_transport_header_was_set(skb))
         return;
 
     if (skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
                          NULL, 0, 0, 0, 0))
         skb_set_transport_header(skb, keys.control.thoff);
 }
 
 static inline void skb_mac_header_rebuild(struct sk_buff *skb)
 {
     if (skb_mac_header_was_set(skb)) {
         const unsigned char *old_mac = skb_mac_header(skb);
 
         skb_set_mac_header(skb, -skb->mac_len);
         memmove(skb_mac_header(skb), old_mac, skb->mac_len);
     }
 }
 
 static inline int skb_checksum_start_offset(const struct sk_buff *skb)
 {
     return skb->csum_start - skb_headroom(skb);
 }
 
 static inline unsigned char *skb_checksum_start(const struct sk_buff *skb)
 {
     return skb->head + skb->csum_start;
 }
 
 static inline int skb_transport_offset(const struct sk_buff *skb)
 {
     return skb_transport_header(skb) - skb->data;
 }
 
 static inline u32 skb_network_header_len(const struct sk_buff *skb)
 {
     return skb->transport_header - skb->network_header;
 }
 
 static inline u32 skb_inner_network_header_len(const struct sk_buff *skb)
 {
     return skb->inner_transport_header - skb->inner_network_header;
 }
 
 static inline int skb_network_offset(const struct sk_buff *skb)
 {
     return skb_network_header(skb) - skb->data;
 }
 
 static inline int skb_inner_network_offset(const struct sk_buff *skb)
 {
     return skb_inner_network_header(skb) - skb->data;
 }
 
 static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len)
 {
     return pskb_may_pull(skb, skb_network_offset(skb) + len);
 }
 
 /*
  * CPUs often take a performance hit when accessing unaligned memory
  * locations. The actual performance hit varies, it can be small if the
  * hardware handles it or large if we have to take an exception and fix it
  * in software.
  *
  * Since an ethernet header is 14 bytes network drivers often end up with
  * the IP header at an unaligned offset. The IP header can be aligned by
  * shifting the start of the packet by 2 bytes. Drivers should do this
  * with:
  *
  * skb_reserve(skb, NET_IP_ALIGN);
  *
  * The downside to this alignment of the IP header is that the DMA is now
  * unaligned. On some architectures the cost of an unaligned DMA is high
  * and this cost outweighs the gains made by aligning the IP header.
  *
  * Since this trade off varies between architectures, we allow NET_IP_ALIGN
  * to be overridden.
  */
 #ifndef NET_IP_ALIGN
 #define NET_IP_ALIGN    2
 #endif
 
 /*
  * The networking layer reserves some headroom in skb data (via
  * dev_alloc_skb). This is used to avoid having to reallocate skb data when
  * the header has to grow. In the default case, if the header has to grow
  * 32 bytes or less we avoid the reallocation.
  *
  * Unfortunately this headroom changes the DMA alignment of the resulting
  * network packet. As for NET_IP_ALIGN, this unaligned DMA is expensive
  * on some architectures. An architecture can override this value,
  * perhaps setting it to a cacheline in size (since that will maintain
  * cacheline alignment of the DMA). It must be a power of 2.
  *
  * Various parts of the networking layer expect at least 32 bytes of
  * headroom, you should not reduce this.
  *
  * Using max(32, L1_CACHE_BYTES) makes sense (especially with RPS)
  * to reduce average number of cache lines per packet.
  * get_rps_cpu() for example only access one 64 bytes aligned block :
  * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
  */
 #ifndef NET_SKB_PAD
 #define NET_SKB_PAD max(32, L1_CACHE_BYTES)
 #endif
 
 int ___pskb_trim(struct sk_buff *skb, unsigned int len);
 
 static inline void __skb_set_length(struct sk_buff *skb, unsigned int len)
 {
     if (WARN_ON(skb_is_nonlinear(skb)))
         return;
     skb->len = len;
     skb_set_tail_pointer(skb, len);
 }
 
 static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
 {
     __skb_set_length(skb, len);
 }
 
 void skb_trim(struct sk_buff *skb, unsigned int len);
 
 static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
 {
     if (skb->data_len)
         return ___pskb_trim(skb, len);
     __skb_trim(skb, len);
     return 0;
 }
 
 static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
 {
     return (len < skb->len) ? __pskb_trim(skb, len) : 0;
 }
 
 /**
  *  pskb_trim_unique - remove end from a paged unique (not cloned) buffer
  *  @skb: buffer to alter
  *  @len: new length
  *
  *  This is identical to pskb_trim except that the caller knows that
  *  the skb is not cloned so we should never get an error due to out-
  *  of-memory.
  */
 static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
 {
     int err = pskb_trim(skb, len);
     BUG_ON(err);
 }
 
 static inline int __skb_grow(struct sk_buff *skb, unsigned int len)
 {
     unsigned int diff = len - skb->len;
 
     if (skb_tailroom(skb) < diff) {
         int ret = pskb_expand_head(skb, 0, diff - skb_tailroom(skb),
                        GFP_ATOMIC);
         if (ret)
             return ret;
     }
     __skb_set_length(skb, len);
     return 0;
 }
 
 /**
  *  skb_orphan - orphan a buffer
  *  @skb: buffer to orphan
  *
  *  If a buffer currently has an owner then we call the owner's
  *  destructor function and make the @skb unowned. The buffer continues
  *  to exist but is no longer charged to its former owner.
  */
 static inline void skb_orphan(struct sk_buff *skb)
 {
     if (skb->destructor) {
         skb->destructor(skb);
         skb->destructor = NULL;
         skb->sk     = NULL;
     } else {
         BUG_ON(skb->sk);
     }
 }
 
 /**
  *  skb_orphan_frags - orphan the frags contained in a buffer
  *  @skb: buffer to orphan frags from
  *  @gfp_mask: allocation mask for replacement pages
  *
  *  For each frag in the SKB which needs a destructor (i.e. has an
  *  owner) create a copy of that frag and release the original
  *  page by calling the destructor.
  */
 static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
 {
     if (likely(!skb_zcopy(skb)))
         return 0;
     if (skb_shinfo(skb)->flags & SKBFL_DONT_ORPHAN)
         return 0;
     return skb_copy_ubufs(skb, gfp_mask);
 }
 
 /* Frags must be orphaned, even if refcounted, if skb might loop to rx path */
 static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask)
 {
     if (likely(!skb_zcopy(skb)))
         return 0;
     return skb_copy_ubufs(skb, gfp_mask);
 }
 
 /**
  *  __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 does not take the
  *  list lock and the caller must hold the relevant locks to use it.
  */
 static inline void __skb_queue_purge(struct sk_buff_head *list)
 {
     struct sk_buff *skb;
     while ((skb = __skb_dequeue(list)) != NULL)
         kfree_skb(skb);
 }
 void skb_queue_purge(struct sk_buff_head *list);
 
 unsigned int skb_rbtree_purge(struct rb_root *root);
 
 void *__netdev_alloc_frag_align(unsigned int fragsz, unsigned int align_mask);
 
 /**
  * netdev_alloc_frag - allocate a page fragment
  * @fragsz: fragment size
  *
  * Allocates a frag from a page for receive buffer.
  * Uses GFP_ATOMIC allocations.
  */
 static inline void *netdev_alloc_frag(unsigned int fragsz)
 {
     return __netdev_alloc_frag_align(fragsz, ~0u);
 }
 
 static inline void *netdev_alloc_frag_align(unsigned int fragsz,
                         unsigned int align)
 {
     WARN_ON_ONCE(!is_power_of_2(align));
     return __netdev_alloc_frag_align(fragsz, -align);
 }
 
 struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int length,
                    gfp_t gfp_mask);
 
 /**
  *  netdev_alloc_skb - allocate an skbuff for rx on a specific device
  *  @dev: network device to receive on
  *  @length: length to allocate
  *
  *  Allocate a new &sk_buff and assign it a usage count of one. The
  *  buffer has unspecified 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. Although this function
  *  allocates memory it can be called from an interrupt.
  */
 static inline struct sk_buff *netdev_alloc_skb(struct net_device *dev,
                            unsigned int length)
 {
     return __netdev_alloc_skb(dev, length, GFP_ATOMIC);
 }
 
 /* legacy helper around __netdev_alloc_skb() */
 static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
                           gfp_t gfp_mask)
 {
     return __netdev_alloc_skb(NULL, length, gfp_mask);
 }
 
 /* legacy helper around netdev_alloc_skb() */
 static inline struct sk_buff *dev_alloc_skb(unsigned int length)
 {
     return netdev_alloc_skb(NULL, length);
 }
 
 
 static inline struct sk_buff *__netdev_alloc_skb_ip_align(struct net_device *dev,
         unsigned int length, gfp_t gfp)
 {
     struct sk_buff *skb = __netdev_alloc_skb(dev, length + NET_IP_ALIGN, gfp);
 
     if (NET_IP_ALIGN && skb)
         skb_reserve(skb, NET_IP_ALIGN);
     return skb;
 }
 
 static inline struct sk_buff *netdev_alloc_skb_ip_align(struct net_device *dev,
         unsigned int length)
 {
     return __netdev_alloc_skb_ip_align(dev, length, GFP_ATOMIC);
 }
 
 static inline void skb_free_frag(void *addr)
 {
     page_frag_free(addr);
 }
 
 void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask);
 
 static inline void *napi_alloc_frag(unsigned int fragsz)
 {
     return __napi_alloc_frag_align(fragsz, ~0u);
 }
 
 static inline void *napi_alloc_frag_align(unsigned int fragsz,
                       unsigned int align)
 {
     WARN_ON_ONCE(!is_power_of_2(align));
     return __napi_alloc_frag_align(fragsz, -align);
 }
 
 struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
                  unsigned int length, gfp_t gfp_mask);
 static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
                          unsigned int length)
 {
     return __napi_alloc_skb(napi, length, GFP_ATOMIC);
 }
 void napi_consume_skb(struct sk_buff *skb, int budget);
 
 void napi_skb_free_stolen_head(struct sk_buff *skb);
 void __kfree_skb_defer(struct sk_buff *skb);
 
 /**
  * __dev_alloc_pages - allocate page for network Rx
  * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
  * @order: size of the allocation
  *
  * Allocate a new page.
  *
  * %NULL is returned if there is no free memory.
 */
 static inline struct page *__dev_alloc_pages(gfp_t gfp_mask,
                          unsigned int order)
 {
     /* This piece of code contains several assumptions.
      * 1.  This is for device Rx, therefor a cold page is preferred.
      * 2.  The expectation is the user wants a compound page.
      * 3.  If requesting a order 0 page it will not be compound
      *     due to the check to see if order has a value in prep_new_page
      * 4.  __GFP_MEMALLOC is ignored if __GFP_NOMEMALLOC is set due to
      *     code in gfp_to_alloc_flags that should be enforcing this.
      */
     gfp_mask |= __GFP_COMP | __GFP_MEMALLOC;
 
     return alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
 }
 
 static inline struct page *dev_alloc_pages(unsigned int order)
 {
     return __dev_alloc_pages(GFP_ATOMIC | __GFP_NOWARN, order);
 }
 
 /**
  * __dev_alloc_page - allocate a page for network Rx
  * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
  *
  * Allocate a new page.
  *
  * %NULL is returned if there is no free memory.
  */
 static inline struct page *__dev_alloc_page(gfp_t gfp_mask)
 {
     return __dev_alloc_pages(gfp_mask, 0);
 }
 
 static inline struct page *dev_alloc_page(void)
 {
     return dev_alloc_pages(0);
 }
 
 /**
  * dev_page_is_reusable - check whether a page can be reused for network Rx
  * @page: the page to test
  *
  * A page shouldn't be considered for reusing/recycling if it was allocated
  * under memory pressure or at a distant memory node.
  *
  * Returns false if this page should be returned to page allocator, true
  * otherwise.
  */
 static inline bool dev_page_is_reusable(const struct page *page)
 {
     return likely(page_to_nid(page) == numa_mem_id() &&
               !page_is_pfmemalloc(page));
 }
 
 /**
  *  skb_propagate_pfmemalloc - Propagate pfmemalloc if skb is allocated after RX page
  *  @page: The page that was allocated from skb_alloc_page
  *  @skb: The skb that may need pfmemalloc set
  */
 static inline void skb_propagate_pfmemalloc(const struct page *page,
                         struct sk_buff *skb)
 {
     if (page_is_pfmemalloc(page))
         skb->pfmemalloc = true;
 }
 
 /**
  * skb_frag_off() - Returns the offset of a skb fragment
  * @frag: the paged fragment
  */
 static inline unsigned int skb_frag_off(const skb_frag_t *frag)
 {
     return frag->bv_offset;
 }
 
 /**
  * skb_frag_off_add() - Increments the offset of a skb fragment by @delta
  * @frag: skb fragment
  * @delta: value to add
  */
 static inline void skb_frag_off_add(skb_frag_t *frag, int delta)
 {
     frag->bv_offset += delta;
 }
 
 /**
  * skb_frag_off_set() - Sets the offset of a skb fragment
  * @frag: skb fragment
  * @offset: offset of fragment
  */
 static inline void skb_frag_off_set(skb_frag_t *frag, unsigned int offset)
 {
     frag->bv_offset = offset;
 }
 
 /**
  * skb_frag_off_copy() - Sets the offset of a skb fragment from another fragment
  * @fragto: skb fragment where offset is set
  * @fragfrom: skb fragment offset is copied from
  */
 static inline void skb_frag_off_copy(skb_frag_t *fragto,
                      const skb_frag_t *fragfrom)
 {
     fragto->bv_offset = fragfrom->bv_offset;
 }
 
 /**
  * skb_frag_page - retrieve the page referred to by a paged fragment
  * @frag: the paged fragment
  *
  * Returns the &struct page associated with @frag.
  */
 static inline struct page *skb_frag_page(const skb_frag_t *frag)
 {
     return frag->bv_page;
 }
 
 /**
  * __skb_frag_ref - take an addition reference on a paged fragment.
  * @frag: the paged fragment
  *
  * Takes an additional reference on the paged fragment @frag.
  */
 static inline void __skb_frag_ref(skb_frag_t *frag)
 {
     get_page(skb_frag_page(frag));
 }
 
 /**
  * skb_frag_ref - take an addition reference on a paged fragment of an skb.
  * @skb: the buffer
  * @f: the fragment offset.
  *
  * Takes an additional reference on the @f'th paged fragment of @skb.
  */
 static inline void skb_frag_ref(struct sk_buff *skb, int f)
 {
     __skb_frag_ref(&skb_shinfo(skb)->frags[f]);
 }
 
 /**
  * __skb_frag_unref - release a reference on a paged fragment.
  * @frag: the paged fragment
  * @recycle: recycle the page if allocated via page_pool
  *
  * Releases a reference on the paged fragment @frag
  * or recycles the page via the page_pool API.
  */
 static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
 {
     struct page *page = skb_frag_page(frag);
 
 #ifdef CONFIG_PAGE_POOL
     if (recycle && page_pool_return_skb_page(page))
         return;
 #endif
     put_page(page);
 }
 
 /**
  * skb_frag_unref - release a reference on a paged fragment of an skb.
  * @skb: the buffer
  * @f: the fragment offset
  *
  * Releases a reference on the @f'th paged fragment of @skb.
  */
 static inline void skb_frag_unref(struct sk_buff *skb, int f)
 {
     struct skb_shared_info *shinfo = skb_shinfo(skb);
 
     if (!skb_zcopy_managed(skb))
         __skb_frag_unref(&shinfo->frags[f], skb->pp_recycle);
 }
 
 /**
  * skb_frag_address - gets the address of the data contained in a paged fragment
  * @frag: the paged fragment buffer
  *
  * Returns the address of the data within @frag. The page must already
  * be mapped.
  */
 static inline void *skb_frag_address(const skb_frag_t *frag)
 {
     return page_address(skb_frag_page(frag)) + skb_frag_off(frag);
 }
 
 /**
  * skb_frag_address_safe - gets the address of the data contained in a paged fragment
  * @frag: the paged fragment buffer
  *
  * Returns the address of the data within @frag. Checks that the page
  * is mapped and returns %NULL otherwise.
  */
 static inline void *skb_frag_address_safe(const skb_frag_t *frag)
 {
     void *ptr = page_address(skb_frag_page(frag));
     if (unlikely(!ptr))
         return NULL;
 
     return ptr + skb_frag_off(frag);
 }
 
 /**
  * skb_frag_page_copy() - sets the page in a fragment from another fragment
  * @fragto: skb fragment where page is set
  * @fragfrom: skb fragment page is copied from
  */
 static inline void skb_frag_page_copy(skb_frag_t *fragto,
                       const skb_frag_t *fragfrom)
 {
     fragto->bv_page = fragfrom->bv_page;
 }
 
 /**
  * __skb_frag_set_page - sets the page contained in a paged fragment
  * @frag: the paged fragment
  * @page: the page to set
  *
  * Sets the fragment @frag to contain @page.
  */
 static inline void __skb_frag_set_page(skb_frag_t *frag, struct page *page)
 {
     frag->bv_page = page;
 }
 
 /**
  * skb_frag_set_page - sets the page contained in a paged fragment of an skb
  * @skb: the buffer
  * @f: the fragment offset
  * @page: the page to set
  *
  * Sets the @f'th fragment of @skb to contain @page.
  */
 static inline void skb_frag_set_page(struct sk_buff *skb, int f,
                      struct page *page)
 {
     __skb_frag_set_page(&skb_shinfo(skb)->frags[f], page);
 }
 
 bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio);
 
 /**
  * skb_frag_dma_map - maps a paged fragment via the DMA API
  * @dev: the device to map the fragment to
  * @frag: the paged fragment to map
  * @offset: the offset within the fragment (starting at the
  *          fragment's own offset)
  * @size: the number of bytes to map
  * @dir: the direction of the mapping (``PCI_DMA_*``)
  *
  * Maps the page associated with @frag to @device.
  */
 static inline dma_addr_t skb_frag_dma_map(struct device *dev,
                       const skb_frag_t *frag,
                       size_t offset, size_t size,
                       enum dma_data_direction dir)
 {
     return dma_map_page(dev, skb_frag_page(frag),
                 skb_frag_off(frag) + offset, size, dir);
 }
 
 static inline struct sk_buff *pskb_copy(struct sk_buff *skb,
                     gfp_t gfp_mask)
 {
     return __pskb_copy(skb, skb_headroom(skb), gfp_mask);
 }
 
 
 static inline struct sk_buff *pskb_copy_for_clone(struct sk_buff *skb,
                           gfp_t gfp_mask)
 {
     return __pskb_copy_fclone(skb, skb_headroom(skb), gfp_mask, true);
 }
 
 
 /**
  *  skb_clone_writable - is the header of a clone writable
  *  @skb: buffer to check
  *  @len: length up to which to write
  *
  *  Returns true if modifying the header part of the cloned buffer
  *  does not requires the data to be copied.
  */
 static inline int skb_clone_writable(const struct sk_buff *skb, unsigned int len)
 {
     return !skb_header_cloned(skb) &&
            skb_headroom(skb) + len <= skb->hdr_len;
 }
 
 static inline int skb_try_make_writable(struct sk_buff *skb,
                     unsigned int write_len)
 {
     return skb_cloned(skb) && !skb_clone_writable(skb, write_len) &&
            pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
 }
 
 static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom,
                 int cloned)
 {
     int delta = 0;
 
     if (headroom > skb_headroom(skb))
         delta = headroom - skb_headroom(skb);
 
     if (delta || cloned)
         return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,
                     GFP_ATOMIC);
     return 0;
 }
 
 /**
  *  skb_cow - copy header of skb when it is required
  *  @skb: buffer to cow
  *  @headroom: needed headroom
  *
  *  If the skb passed lacks sufficient headroom or its data part
  *  is shared, data is reallocated. If reallocation fails, an error
  *  is returned and original skb is not changed.
  *
  *  The result is skb with writable area skb->head...skb->tail
  *  and at least @headroom of space at head.
  */
 static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
 {
     return __skb_cow(skb, headroom, skb_cloned(skb));
 }
 
 /**
  *  skb_cow_head - skb_cow but only making the head writable
  *  @skb: buffer to cow
  *  @headroom: needed headroom
  *
  *  This function is identical to skb_cow except that we replace the
  *  skb_cloned check by skb_header_cloned.  It should be used when
  *  you only need to push on some header and do not need to modify
  *  the data.
  */
 static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
 {
     return __skb_cow(skb, headroom, skb_header_cloned(skb));
 }
 
 /**
  *  skb_padto   - pad an skbuff up to a minimal size
  *  @skb: buffer to pad
  *  @len: minimal length
  *
  *  Pads up a buffer to ensure the trailing bytes exist and are
  *  blanked. If the buffer already contains sufficient data it
  *  is untouched. Otherwise it is extended. Returns zero on
  *  success. The skb is freed on error.
  */
 static inline int skb_padto(struct sk_buff *skb, unsigned int len)
 {
     unsigned int size = skb->len;
     if (likely(size >= len))
         return 0;
     return skb_pad(skb, len - size);
 }
 
 /**
  *  __skb_put_padto - increase size and pad an skbuff up to a minimal size
  *  @skb: buffer to pad
  *  @len: minimal length
  *  @free_on_error: free buffer on error
  *
  *  Pads up a buffer to ensure the trailing bytes exist and are
  *  blanked. If the buffer already contains sufficient data it
  *  is untouched. Otherwise it is extended. Returns zero on
  *  success. The skb is freed on error if @free_on_error is true.
  */
 static inline int __must_check __skb_put_padto(struct sk_buff *skb,
                            unsigned int len,
                            bool free_on_error)
 {
     unsigned int size = skb->len;
 
     if (unlikely(size < len)) {
         len -= size;
         if (__skb_pad(skb, len, free_on_error))
             return -ENOMEM;
         __skb_put(skb, len);
     }
     return 0;
 }
 
 /**
  *  skb_put_padto - increase size and pad an skbuff up to a minimal size
  *  @skb: buffer to pad
  *  @len: minimal length
  *
  *  Pads up a buffer to ensure the trailing bytes exist and are
  *  blanked. If the buffer already contains sufficient data it
  *  is untouched. Otherwise it is extended. Returns zero on
  *  success. The skb is freed on error.
  */
 static inline int __must_check skb_put_padto(struct sk_buff *skb, unsigned int len)
 {
     return __skb_put_padto(skb, len, true);
 }
 
 static inline int skb_add_data(struct sk_buff *skb,
                    struct iov_iter *from, int copy)
 {
     const int off = skb->len;
 
     if (skb->ip_summed == CHECKSUM_NONE) {
         __wsum csum = 0;
         if (csum_and_copy_from_iter_full(skb_put(skb, copy), copy,
                              &csum, from)) {
             skb->csum = csum_block_add(skb->csum, csum, off);
             return 0;
         }
     } else if (copy_from_iter_full(skb_put(skb, copy), copy, from))
         return 0;
 
     __skb_trim(skb, off);
     return -EFAULT;
 }
 
 static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
                     const struct page *page, int off)
 {
     if (skb_zcopy(skb))
         return false;
     if (i) {
         const skb_frag_t *frag = &skb_shinfo(skb)->frags[i - 1];
 
         return page == skb_frag_page(frag) &&
                off == skb_frag_off(frag) + skb_frag_size(frag);
     }
     return false;
 }
 
 static inline int __skb_linearize(struct sk_buff *skb)
 {
     return __pskb_pull_tail(skb, skb->data_len) ? 0 : -ENOMEM;
 }
 
 /**
  *  skb_linearize - convert paged skb to linear one
  *  @skb: buffer to linarize
  *
  *  If there is no free memory -ENOMEM is returned, otherwise zero
  *  is returned and the old skb data released.
  */
 static inline int skb_linearize(struct sk_buff *skb)
 {
     return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
 }
 
 /**
  * skb_has_shared_frag - can any frag be overwritten
  * @skb: buffer to test
  *
  * Return true if the skb has at least one frag that might be modified
  * by an external entity (as in vmsplice()/sendfile())
  */
 static inline bool skb_has_shared_frag(const struct sk_buff *skb)
 {
     return skb_is_nonlinear(skb) &&
            skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG;
 }
 
 /**
  *  skb_linearize_cow - make sure skb is linear and writable
  *  @skb: buffer to process
  *
  *  If there is no free memory -ENOMEM is returned, otherwise zero
  *  is returned and the old skb data released.
  */
 static inline int skb_linearize_cow(struct sk_buff *skb)
 {
     return skb_is_nonlinear(skb) || skb_cloned(skb) ?
            __skb_linearize(skb) : 0;
 }
 
 static __always_inline void
 __skb_postpull_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
              unsigned int off)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->csum = csum_block_sub(skb->csum,
                        csum_partial(start, len, 0), off);
     else if (skb->ip_summed == CHECKSUM_PARTIAL &&
          skb_checksum_start_offset(skb) < 0)
         skb->ip_summed = CHECKSUM_NONE;
 }
 
 /**
  *  skb_postpull_rcsum - update checksum for received skb after pull
  *  @skb: buffer to update
  *  @start: start of data before pull
  *  @len: length of data pulled
  *
  *  After doing a pull on a received packet, you need to call this to
  *  update the CHECKSUM_COMPLETE checksum, or set ip_summed to
  *  CHECKSUM_NONE so that it can be recomputed from scratch.
  */
 static inline void skb_postpull_rcsum(struct sk_buff *skb,
                       const void *start, unsigned int len)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->csum = wsum_negate(csum_partial(start, len,
                              wsum_negate(skb->csum)));
     else if (skb->ip_summed == CHECKSUM_PARTIAL &&
          skb_checksum_start_offset(skb) < 0)
         skb->ip_summed = CHECKSUM_NONE;
 }
 
 static __always_inline void
 __skb_postpush_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
              unsigned int off)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->csum = csum_block_add(skb->csum,
                        csum_partial(start, len, 0), off);
 }
 
 /**
  *  skb_postpush_rcsum - update checksum for received skb after push
  *  @skb: buffer to update
  *  @start: start of data after push
  *  @len: length of data pushed
  *
  *  After doing a push on a received packet, you need to call this to
  *  update the CHECKSUM_COMPLETE checksum.
  */
 static inline void skb_postpush_rcsum(struct sk_buff *skb,
                       const void *start, unsigned int len)
 {
     __skb_postpush_rcsum(skb, start, len, 0);
 }
 
 void *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
 
 /**
  *  skb_push_rcsum - push skb and update receive checksum
  *  @skb: buffer to update
  *  @len: length of data pulled
  *
  *  This function performs an skb_push on the packet and updates
  *  the CHECKSUM_COMPLETE checksum.  It should be used on
  *  receive path processing instead of skb_push unless you know
  *  that the checksum difference is zero (e.g., a valid IP header)
  *  or you are setting ip_summed to CHECKSUM_NONE.
  */
 static inline void *skb_push_rcsum(struct sk_buff *skb, unsigned int len)
 {
     skb_push(skb, len);
     skb_postpush_rcsum(skb, skb->data, len);
     return skb->data;
 }
 
 int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len);
 /**
  *  pskb_trim_rcsum - trim received skb and update checksum
  *  @skb: buffer to trim
  *  @len: new length
  *
  *  This is exactly the same as pskb_trim except that it ensures the
  *  checksum of received packets are still valid after the operation.
  *  It can change skb pointers.
  */
 
 static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
 {
     if (likely(len >= skb->len))
         return 0;
     return pskb_trim_rcsum_slow(skb, len);
 }
 
 static inline int __skb_trim_rcsum(struct sk_buff *skb, unsigned int len)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->ip_summed = CHECKSUM_NONE;
     __skb_trim(skb, len);
     return 0;
 }
 
 static inline int __skb_grow_rcsum(struct sk_buff *skb, unsigned int len)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->ip_summed = CHECKSUM_NONE;
     return __skb_grow(skb, len);
 }
 
 #define rb_to_skb(rb) rb_entry_safe(rb, struct sk_buff, rbnode)
 #define skb_rb_first(root) rb_to_skb(rb_first(root))
 #define skb_rb_last(root)  rb_to_skb(rb_last(root))
 #define skb_rb_next(skb)   rb_to_skb(rb_next(&(skb)->rbnode))
 #define skb_rb_prev(skb)   rb_to_skb(rb_prev(&(skb)->rbnode))
 
 #define skb_queue_walk(queue, skb) \
         for (skb = (queue)->next;                   \
              skb != (struct sk_buff *)(queue);              \
              skb = skb->next)
 
 #define skb_queue_walk_safe(queue, skb, tmp)                    \
         for (skb = (queue)->next, tmp = skb->next;          \
              skb != (struct sk_buff *)(queue);              \
              skb = tmp, tmp = skb->next)
 
 #define skb_queue_walk_from(queue, skb)                     \
         for (; skb != (struct sk_buff *)(queue);            \
              skb = skb->next)
 
 #define skb_rbtree_walk(skb, root)                      \
         for (skb = skb_rb_first(root); skb != NULL;         \
              skb = skb_rb_next(skb))
 
 #define skb_rbtree_walk_from(skb)                       \
         for (; skb != NULL;                     \
              skb = skb_rb_next(skb))
 
 #define skb_rbtree_walk_from_safe(skb, tmp)                 \
         for (; tmp = skb ? skb_rb_next(skb) : NULL, (skb != NULL);  \
              skb = tmp)
 
 #define skb_queue_walk_from_safe(queue, skb, tmp)               \
         for (tmp = skb->next;                       \
              skb != (struct sk_buff *)(queue);              \
              skb = tmp, tmp = skb->next)
 
 #define skb_queue_reverse_walk(queue, skb) \
         for (skb = (queue)->prev;                   \
              skb != (struct sk_buff *)(queue);              \
              skb = skb->prev)
 
 #define skb_queue_reverse_walk_safe(queue, skb, tmp)                \
         for (skb = (queue)->prev, tmp = skb->prev;          \
              skb != (struct sk_buff *)(queue);              \
              skb = tmp, tmp = skb->prev)
 
 #define skb_queue_reverse_walk_from_safe(queue, skb, tmp)           \
         for (tmp = skb->prev;                       \
              skb != (struct sk_buff *)(queue);              \
              skb = tmp, tmp = skb->prev)
 
 static inline bool skb_has_frag_list(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->frag_list != NULL;
 }
 
 static inline void skb_frag_list_init(struct sk_buff *skb)
 {
     skb_shinfo(skb)->frag_list = NULL;
 }
 
 #define skb_walk_frags(skb, iter)   \
     for (iter = skb_shinfo(skb)->frag_list; iter; iter = iter->next)
 
 
 int __skb_wait_for_more_packets(struct sock *sk, struct sk_buff_head *queue,
                 int *err, long *timeo_p,
                 const struct sk_buff *skb);
 struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
                       struct sk_buff_head *queue,
                       unsigned int flags,
                       int *off, int *err,
                       struct sk_buff **last);
 struct sk_buff *__skb_try_recv_datagram(struct sock *sk,
                     struct sk_buff_head *queue,
                     unsigned int flags, int *off, int *err,
                     struct sk_buff **last);
 struct sk_buff *__skb_recv_datagram(struct sock *sk,
                     struct sk_buff_head *sk_queue,
                     unsigned int flags, int *off, int *err);
 struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned int flags, int *err);
 __poll_t datagram_poll(struct file *file, struct socket *sock,
                struct poll_table_struct *wait);
 int skb_copy_datagram_iter(const struct sk_buff *from, int offset,
                struct iov_iter *to, int size);
 static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
                     struct msghdr *msg, int size)
 {
     return skb_copy_datagram_iter(from, offset, &msg->msg_iter, size);
 }
 int skb_copy_and_csum_datagram_msg(struct sk_buff *skb, int hlen,
                    struct msghdr *msg);
 int skb_copy_and_hash_datagram_iter(const struct sk_buff *skb, int offset,
                struct iov_iter *to, int len,
                struct ahash_request *hash);
 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
                  struct iov_iter *from, int len);
 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
 void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
 static inline void skb_free_datagram_locked(struct sock *sk,
                         struct sk_buff *skb)
 {
     __skb_free_datagram_locked(sk, skb, 0);
 }
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
 int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);
 __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, u8 *to,
                   int len);
 int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
             struct pipe_inode_info *pipe, unsigned int len,
             unsigned int flags);
 int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
              int len);
 int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len);
 void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
 unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
 int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
          int len, int hlen);
 void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len);
 int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
 void skb_scrub_packet(struct sk_buff *skb, bool xnet);
 bool skb_gso_validate_network_len(const struct sk_buff *skb, unsigned int mtu);
 bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);
 struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
 struct sk_buff *skb_segment_list(struct sk_buff *skb, netdev_features_t features,
                  unsigned int offset);
 struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
 int skb_ensure_writable(struct sk_buff *skb, unsigned int write_len);
 int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci);
 int skb_vlan_pop(struct sk_buff *skb);
 int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
 int skb_eth_pop(struct sk_buff *skb);
 int skb_eth_push(struct sk_buff *skb, const unsigned char *dst,
          const unsigned char *src);
 int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
           int mac_len, bool ethernet);
 int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
          bool ethernet);
 int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse);
 int skb_mpls_dec_ttl(struct sk_buff *skb);
 struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
                  gfp_t gfp);
 
 static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
 {
     return copy_from_iter_full(data, len, &msg->msg_iter) ? 0 : -EFAULT;
 }
 
 static inline int memcpy_to_msg(struct msghdr *msg, void *data, int len)
 {
     return copy_to_iter(data, len, &msg->msg_iter) == len ? 0 : -EFAULT;
 }
 
 struct skb_checksum_ops {
     __wsum (*update)(const void *mem, int len, __wsum wsum);
     __wsum (*combine)(__wsum csum, __wsum csum2, int offset, int len);
 };
 
 extern const struct skb_checksum_ops *crc32c_csum_stub __read_mostly;
 
 __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
               __wsum csum, const struct skb_checksum_ops *ops);
 __wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
             __wsum csum);
 
 static inline void * __must_check
 __skb_header_pointer(const struct sk_buff *skb, int offset, int len,
              const void *data, int hlen, void *buffer)
 {
     if (likely(hlen - offset >= len))
         return (void *)data + offset;
 
     if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
         return NULL;
 
     return buffer;
 }
 
 static inline void * __must_check
 skb_header_pointer(const struct sk_buff *skb, int offset, int len, void *buffer)
 {
     return __skb_header_pointer(skb, offset, len, skb->data,
                     skb_headlen(skb), buffer);
 }
 
 /**
  *  skb_needs_linearize - check if we need to linearize a given skb
  *                depending on the given device features.
  *  @skb: socket buffer to check
  *  @features: net device features
  *
  *  Returns true if either:
  *  1. skb has frag_list and the device doesn't support FRAGLIST, or
  *  2. skb is fragmented and the device does not support SG.
  */
 static inline bool skb_needs_linearize(struct sk_buff *skb,
                        netdev_features_t features)
 {
     return skb_is_nonlinear(skb) &&
            ((skb_has_frag_list(skb) && !(features & NETIF_F_FRAGLIST)) ||
         (skb_shinfo(skb)->nr_frags && !(features & NETIF_F_SG)));
 }
 
 static inline void skb_copy_from_linear_data(const struct sk_buff *skb,
                          void *to,
                          const unsigned int len)
 {
     memcpy(to, skb->data, len);
 }
 
 static inline void skb_copy_from_linear_data_offset(const struct sk_buff *skb,
                             const int offset, void *to,
                             const unsigned int len)
 {
     memcpy(to, skb->data + offset, len);
 }
 
 static inline void skb_copy_to_linear_data(struct sk_buff *skb,
                        const void *from,
                        const unsigned int len)
 {
     memcpy(skb->data, from, len);
 }
 
 static inline void skb_copy_to_linear_data_offset(struct sk_buff *skb,
                           const int offset,
                           const void *from,
                           const unsigned int len)
 {
     memcpy(skb->data + offset, from, len);
 }
 
 void skb_init(void);
 
 static inline ktime_t skb_get_ktime(const struct sk_buff *skb)
 {
     return skb->tstamp;
 }
 
 /**
  *  skb_get_timestamp - get timestamp from a skb
  *  @skb: skb to get stamp from
  *  @stamp: pointer to struct __kernel_old_timeval to store stamp in
  *
  *  Timestamps are stored in the skb as offsets to a base timestamp.
  *  This function converts the offset back to a struct timeval and stores
  *  it in stamp.
  */
 static inline void skb_get_timestamp(const struct sk_buff *skb,
                      struct __kernel_old_timeval *stamp)
 {
     *stamp = ns_to_kernel_old_timeval(skb->tstamp);
 }
 
 static inline void skb_get_new_timestamp(const struct sk_buff *skb,
                      struct __kernel_sock_timeval *stamp)
 {
     struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
 
     stamp->tv_sec = ts.tv_sec;
     stamp->tv_usec = ts.tv_nsec / 1000;
 }
 
 static inline void skb_get_timestampns(const struct sk_buff *skb,
                        struct __kernel_old_timespec *stamp)
 {
     struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
 
     stamp->tv_sec = ts.tv_sec;
     stamp->tv_nsec = ts.tv_nsec;
 }
 
 static inline void skb_get_new_timestampns(const struct sk_buff *skb,
                        struct __kernel_timespec *stamp)
 {
     struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
 
     stamp->tv_sec = ts.tv_sec;
     stamp->tv_nsec = ts.tv_nsec;
 }
 
 static inline void __net_timestamp(struct sk_buff *skb)
 {
     skb->tstamp = ktime_get_real();
     skb->mono_delivery_time = 0;
 }
 
 static inline ktime_t net_timedelta(ktime_t t)
 {
     return ktime_sub(ktime_get_real(), t);
 }
 
 static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
                      bool mono)
 {
     skb->tstamp = kt;
     skb->mono_delivery_time = kt && mono;
 }
 
 DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
 
 /* It is used in the ingress path to clear the delivery_time.
  * If needed, set the skb->tstamp to the (rcv) timestamp.
  */
 static inline void skb_clear_delivery_time(struct sk_buff *skb)
 {
     if (skb->mono_delivery_time) {
         skb->mono_delivery_time = 0;
         if (static_branch_unlikely(&netstamp_needed_key))
             skb->tstamp = ktime_get_real();
         else
             skb->tstamp = 0;
     }
 }
 
 static inline void skb_clear_tstamp(struct sk_buff *skb)
 {
     if (skb->mono_delivery_time)
         return;
 
     skb->tstamp = 0;
 }
 
 static inline ktime_t skb_tstamp(const struct sk_buff *skb)
 {
     if (skb->mono_delivery_time)
         return 0;
 
     return skb->tstamp;
 }
 
 static inline ktime_t skb_tstamp_cond(const struct sk_buff *skb, bool cond)
 {
     if (!skb->mono_delivery_time && skb->tstamp)
         return skb->tstamp;
 
     if (static_branch_unlikely(&netstamp_needed_key) || cond)
         return ktime_get_real();
 
     return 0;
 }
 
 static inline u8 skb_metadata_len(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->meta_len;
 }
 
 static inline void *skb_metadata_end(const struct sk_buff *skb)
 {
     return skb_mac_header(skb);
 }
 
 static inline bool __skb_metadata_differs(const struct sk_buff *skb_a,
                       const struct sk_buff *skb_b,
                       u8 meta_len)
 {
     const void *a = skb_metadata_end(skb_a);
     const void *b = skb_metadata_end(skb_b);
     /* Using more efficient varaiant than plain call to memcmp(). */
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
     u64 diffs = 0;
 
     switch (meta_len) {
 #define __it(x, op) (x -= sizeof(u##op))
 #define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op))
     case 32: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case 24: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case 16: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case  8: diffs |= __it_diff(a, b, 64);
         break;
     case 28: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case 20: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case 12: diffs |= __it_diff(a, b, 64);
         fallthrough;
     case  4: diffs |= __it_diff(a, b, 32);
         break;
     }
     return diffs;
 #else
     return memcmp(a - meta_len, b - meta_len, meta_len);
 #endif
 }
 
 static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
                     const struct sk_buff *skb_b)
 {
     u8 len_a = skb_metadata_len(skb_a);
     u8 len_b = skb_metadata_len(skb_b);
 
     if (!(len_a | len_b))
         return false;
 
     return len_a != len_b ?
            true : __skb_metadata_differs(skb_a, skb_b, len_a);
 }
 
 static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
 {
     skb_shinfo(skb)->meta_len = meta_len;
 }
 
 static inline void skb_metadata_clear(struct sk_buff *skb)
 {
     skb_metadata_set(skb, 0);
 }
 
 struct sk_buff *skb_clone_sk(struct sk_buff *skb);
 
 #ifdef CONFIG_NETWORK_PHY_TIMESTAMPING
 
 void skb_clone_tx_timestamp(struct sk_buff *skb);
 bool skb_defer_rx_timestamp(struct sk_buff *skb);
 
 #else /* CONFIG_NETWORK_PHY_TIMESTAMPING */
 
 static inline void skb_clone_tx_timestamp(struct sk_buff *skb)
 {
 }
 
 static inline bool skb_defer_rx_timestamp(struct sk_buff *skb)
 {
     return false;
 }
 
 #endif /* !CONFIG_NETWORK_PHY_TIMESTAMPING */
 
 /**
  * skb_complete_tx_timestamp() - deliver cloned skb with tx timestamps
  *
  * PHY drivers may accept clones of transmitted packets for
  * timestamping via their phy_driver.txtstamp method. These drivers
  * must call this function to return the skb back to the stack with a
  * timestamp.
  *
  * @skb: clone of the original outgoing packet
  * @hwtstamps: hardware time stamps
  *
  */
 void skb_complete_tx_timestamp(struct sk_buff *skb,
                    struct skb_shared_hwtstamps *hwtstamps);
 
 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);
 
 /**
  * skb_tstamp_tx - queue clone of skb with send time stamps
  * @orig_skb:   the original outgoing packet
  * @hwtstamps:  hardware time stamps, may be NULL if not available
  *
  * If the skb has a socket associated, then this function clones the
  * skb (thus sharing the actual data and optional structures), stores
  * the optional hardware time stamping information (if non NULL) or
  * generates a software time stamp (otherwise), then queues the clone
  * to the error queue of the socket.  Errors are silently ignored.
  */
 void skb_tstamp_tx(struct sk_buff *orig_skb,
            struct skb_shared_hwtstamps *hwtstamps);
 
 /**
  * skb_tx_timestamp() - Driver hook for transmit timestamping
  *
  * Ethernet MAC Drivers should call this function in their hard_xmit()
  * function immediately before giving the sk_buff to the MAC hardware.
  *
  * Specifically, one should make absolutely sure that this function is
  * called before TX completion of this packet can trigger.  Otherwise
  * the packet could potentially already be freed.
  *
  * @skb: A socket buffer.
  */
 static inline void skb_tx_timestamp(struct sk_buff *skb)
 {
     skb_clone_tx_timestamp(skb);
     if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
         skb_tstamp_tx(skb, NULL);
 }
 
 /**
  * skb_complete_wifi_ack - deliver skb with wifi status
  *
  * @skb: the original outgoing packet
  * @acked: ack status
  *
  */
 void skb_complete_wifi_ack(struct sk_buff *skb, bool acked);
 
 __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len);
 __sum16 __skb_checksum_complete(struct sk_buff *skb);
 
 static inline int skb_csum_unnecessary(const struct sk_buff *skb)
 {
     return ((skb->ip_summed == CHECKSUM_UNNECESSARY) ||
         skb->csum_valid ||
         (skb->ip_summed == CHECKSUM_PARTIAL &&
          skb_checksum_start_offset(skb) >= 0));
 }
 
 /**
  *  skb_checksum_complete - Calculate checksum of an entire packet
  *  @skb: packet to process
  *
  *  This function calculates the checksum over the entire packet plus
  *  the value of skb->csum.  The latter can be used to supply the
  *  checksum of a pseudo header as used by TCP/UDP.  It returns the
  *  checksum.
  *
  *  For protocols that contain complete checksums such as ICMP/TCP/UDP,
  *  this function can be used to verify that checksum on received
  *  packets.  In that case the function should return zero if the
  *  checksum is correct.  In particular, this function will return zero
  *  if skb->ip_summed is CHECKSUM_UNNECESSARY which indicates that the
  *  hardware has already verified the correctness of the checksum.
  */
 static inline __sum16 skb_checksum_complete(struct sk_buff *skb)
 {
     return skb_csum_unnecessary(skb) ?
            0 : __skb_checksum_complete(skb);
 }
 
 static inline void __skb_decr_checksum_unnecessary(struct sk_buff *skb)
 {
     if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
         if (skb->csum_level == 0)
             skb->ip_summed = CHECKSUM_NONE;
         else
             skb->csum_level--;
     }
 }
 
 static inline void __skb_incr_checksum_unnecessary(struct sk_buff *skb)
 {
     if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
         if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
             skb->csum_level++;
     } else if (skb->ip_summed == CHECKSUM_NONE) {
         skb->ip_summed = CHECKSUM_UNNECESSARY;
         skb->csum_level = 0;
     }
 }
 
 static inline void __skb_reset_checksum_unnecessary(struct sk_buff *skb)
 {
     if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
         skb->ip_summed = CHECKSUM_NONE;
         skb->csum_level = 0;
     }
 }
 
 /* Check if we need to perform checksum complete validation.
  *
  * Returns true if checksum complete is needed, false otherwise
  * (either checksum is unnecessary or zero checksum is allowed).
  */
 static inline bool __skb_checksum_validate_needed(struct sk_buff *skb,
                           bool zero_okay,
                           __sum16 check)
 {
     if (skb_csum_unnecessary(skb) || (zero_okay && !check)) {
         skb->csum_valid = 1;
         __skb_decr_checksum_unnecessary(skb);
         return false;
     }
 
     return true;
 }
 
 /* For small packets <= CHECKSUM_BREAK perform checksum complete directly
  * in checksum_init.
  */
 #define CHECKSUM_BREAK 76
 
 /* Unset checksum-complete
  *
  * Unset checksum complete can be done when packet is being modified
  * (uncompressed for instance) and checksum-complete value is
  * invalidated.
  */
 static inline void skb_checksum_complete_unset(struct sk_buff *skb)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->ip_summed = CHECKSUM_NONE;
 }
 
 /* Validate (init) checksum based on checksum complete.
  *
  * Return values:
  *   0: checksum is validated or try to in skb_checksum_complete. In the latter
  *  case the ip_summed will not be CHECKSUM_UNNECESSARY and the pseudo
  *  checksum is stored in skb->csum for use in __skb_checksum_complete
  *   non-zero: value of invalid checksum
  *
  */
 static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
                                bool complete,
                                __wsum psum)
 {
     if (skb->ip_summed == CHECKSUM_COMPLETE) {
         if (!csum_fold(csum_add(psum, skb->csum))) {
             skb->csum_valid = 1;
             return 0;
         }
     }
 
     skb->csum = psum;
 
     if (complete || skb->len <= CHECKSUM_BREAK) {
         __sum16 csum;
 
         csum = __skb_checksum_complete(skb);
         skb->csum_valid = !csum;
         return csum;
     }
 
     return 0;
 }
 
 static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
 {
     return 0;
 }
 
 /* Perform checksum validate (init). Note that this is a macro since we only
  * want to calculate the pseudo header which is an input function if necessary.
  * First we try to validate without any computation (checksum unnecessary) and
  * then calculate based on checksum complete calling the function to compute
  * pseudo header.
  *
  * Return values:
  *   0: checksum is validated or try to in skb_checksum_complete
  *   non-zero: value of invalid checksum
  */
 #define __skb_checksum_validate(skb, proto, complete,           \
                 zero_okay, check, compute_pseudo)   \
 ({                                  \
     __sum16 __ret = 0;                      \
     skb->csum_valid = 0;                        \
     if (__skb_checksum_validate_needed(skb, zero_okay, check))  \
         __ret = __skb_checksum_validate_complete(skb,       \
                 complete, compute_pseudo(skb, proto));  \
     __ret;                              \
 })
 
 #define skb_checksum_init(skb, proto, compute_pseudo)           \
     __skb_checksum_validate(skb, proto, false, false, 0, compute_pseudo)
 
 #define skb_checksum_init_zero_check(skb, proto, check, compute_pseudo) \
     __skb_checksum_validate(skb, proto, false, true, check, compute_pseudo)
 
 #define skb_checksum_validate(skb, proto, compute_pseudo)       \
     __skb_checksum_validate(skb, proto, true, false, 0, compute_pseudo)
 
 #define skb_checksum_validate_zero_check(skb, proto, check,     \
                      compute_pseudo)        \
     __skb_checksum_validate(skb, proto, true, true, check, compute_pseudo)
 
 #define skb_checksum_simple_validate(skb)               \
     __skb_checksum_validate(skb, 0, true, false, 0, null_compute_pseudo)
 
 static inline bool __skb_checksum_convert_check(struct sk_buff *skb)
 {
     return (skb->ip_summed == CHECKSUM_NONE && skb->csum_valid);
 }
 
 static inline void __skb_checksum_convert(struct sk_buff *skb, __wsum pseudo)
 {
     skb->csum = ~pseudo;
     skb->ip_summed = CHECKSUM_COMPLETE;
 }
 
 #define skb_checksum_try_convert(skb, proto, compute_pseudo)    \
 do {                                    \
     if (__skb_checksum_convert_check(skb))              \
         __skb_checksum_convert(skb, compute_pseudo(skb, proto)); \
 } while (0)
 
 static inline void skb_remcsum_adjust_partial(struct sk_buff *skb, void *ptr,
                           u16 start, u16 offset)
 {
     skb->ip_summed = CHECKSUM_PARTIAL;
     skb->csum_start = ((unsigned char *)ptr + start) - skb->head;
     skb->csum_offset = offset - start;
 }
 
 /* Update skbuf and packet to reflect the remote checksum offload operation.
  * When called, ptr indicates the starting point for skb->csum when
  * ip_summed is CHECKSUM_COMPLETE. If we need create checksum complete
  * here, skb_postpull_rcsum is done so skb->csum start is ptr.
  */
 static inline void skb_remcsum_process(struct sk_buff *skb, void *ptr,
                        int start, int offset, bool nopartial)
 {
     __wsum delta;
 
     if (!nopartial) {
         skb_remcsum_adjust_partial(skb, ptr, start, offset);
         return;
     }
 
     if (unlikely(skb->ip_summed != CHECKSUM_COMPLETE)) {
         __skb_checksum_complete(skb);
         skb_postpull_rcsum(skb, skb->data, ptr - (void *)skb->data);
     }
 
     delta = remcsum_adjust(ptr, skb->csum, start, offset);
 
     /* Adjust skb->csum since we changed the packet */
     skb->csum = csum_add(skb->csum, delta);
 }
 
 static inline struct nf_conntrack *skb_nfct(const struct sk_buff *skb)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
     return (void *)(skb->_nfct & NFCT_PTRMASK);
 #else
     return NULL;
 #endif
 }
 
 static inline unsigned long skb_get_nfct(const struct sk_buff *skb)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
     return skb->_nfct;
 #else
     return 0UL;
 #endif
 }
 
 static inline void skb_set_nfct(struct sk_buff *skb, unsigned long nfct)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
     skb->slow_gro |= !!nfct;
     skb->_nfct = nfct;
 #endif
 }
 
 #ifdef CONFIG_SKB_EXTENSIONS
 enum skb_ext_id {
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
     SKB_EXT_BRIDGE_NF,
 #endif
 #ifdef CONFIG_XFRM
     SKB_EXT_SEC_PATH,
 #endif
 #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
     TC_SKB_EXT,
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
     SKB_EXT_MPTCP,
 #endif
 #if IS_ENABLED(CONFIG_MCTP_FLOWS)
     SKB_EXT_MCTP,
 #endif
     SKB_EXT_NUM, /* must be last */
 };
 
 /**
  *  struct skb_ext - sk_buff extensions
  *  @refcnt: 1 on allocation, deallocated on 0
  *  @offset: offset to add to @data to obtain extension address
  *  @chunks: size currently allocated, stored in SKB_EXT_ALIGN_SHIFT units
  *  @data: start of extension data, variable sized
  *
  *  Note: offsets/lengths are stored in chunks of 8 bytes, this allows
  *  to use 'u8' types while allowing up to 2kb worth of extension data.
  */
 struct skb_ext {
     refcount_t refcnt;
     u8 offset[SKB_EXT_NUM]; /* in chunks of 8 bytes */
     u8 chunks;      /* same */
     char data[] __aligned(8);
 };
 
 struct skb_ext *__skb_ext_alloc(gfp_t flags);
 void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
             struct skb_ext *ext);
 void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id);
 void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id);
 void __skb_ext_put(struct skb_ext *ext);
 
 static inline void skb_ext_put(struct sk_buff *skb)
 {
     if (skb->active_extensions)
         __skb_ext_put(skb->extensions);
 }
 
 static inline void __skb_ext_copy(struct sk_buff *dst,
                   const struct sk_buff *src)
 {
     dst->active_extensions = src->active_extensions;
 
     if (src->active_extensions) {
         struct skb_ext *ext = src->extensions;
 
         refcount_inc(&ext->refcnt);
         dst->extensions = ext;
     }
 }
 
 static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *src)
 {
     skb_ext_put(dst);
     __skb_ext_copy(dst, src);
 }
 
 static inline bool __skb_ext_exist(const struct skb_ext *ext, enum skb_ext_id i)
 {
     return !!ext->offset[i];
 }
 
 static inline bool skb_ext_exist(const struct sk_buff *skb, enum skb_ext_id id)
 {
     return skb->active_extensions & (1 << id);
 }
 
 static inline void skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
 {
     if (skb_ext_exist(skb, id))
         __skb_ext_del(skb, id);
 }
 
 static inline void *skb_ext_find(const struct sk_buff *skb, enum skb_ext_id id)
 {
     if (skb_ext_exist(skb, id)) {
         struct skb_ext *ext = skb->extensions;
 
         return (void *)ext + (ext->offset[id] << 3);
     }
 
     return NULL;
 }
 
 static inline void skb_ext_reset(struct sk_buff *skb)
 {
     if (unlikely(skb->active_extensions)) {
         __skb_ext_put(skb->extensions);
         skb->active_extensions = 0;
     }
 }
 
 static inline bool skb_has_extensions(struct sk_buff *skb)
 {
     return unlikely(skb->active_extensions);
 }
 #else
 static inline void skb_ext_put(struct sk_buff *skb) {}
 static inline void skb_ext_reset(struct sk_buff *skb) {}
 static inline void skb_ext_del(struct sk_buff *skb, int unused) {}
 static inline void __skb_ext_copy(struct sk_buff *d, const struct sk_buff *s) {}
 static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *s) {}
 static inline bool skb_has_extensions(struct sk_buff *skb) { return false; }
 #endif /* CONFIG_SKB_EXTENSIONS */
 
 static inline void nf_reset_ct(struct sk_buff *skb)
 {
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
     nf_conntrack_put(skb_nfct(skb));
     skb->_nfct = 0;
 #endif
 }
 
 static inline void nf_reset_trace(struct sk_buff *skb)
 {
 #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
     skb->nf_trace = 0;
 #endif
 }
 
 static inline void ipvs_reset(struct sk_buff *skb)
 {
 #if IS_ENABLED(CONFIG_IP_VS)
     skb->ipvs_property = 0;
 #endif
 }
 
 /* Note: This doesn't put any conntrack info in dst. */
 static inline void __nf_copy(struct sk_buff *dst, const struct sk_buff *src,
                  bool copy)
 {
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
     dst->_nfct = src->_nfct;
     nf_conntrack_get(skb_nfct(src));
 #endif
 #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
     if (copy)
         dst->nf_trace = src->nf_trace;
 #endif
 }
 
 static inline void nf_copy(struct sk_buff *dst, const struct sk_buff *src)
 {
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
     nf_conntrack_put(skb_nfct(dst));
 #endif
     dst->slow_gro = src->slow_gro;
     __nf_copy(dst, src, true);
 }
 
 #ifdef CONFIG_NETWORK_SECMARK
 static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
 {
     to->secmark = from->secmark;
 }
 
 static inline void skb_init_secmark(struct sk_buff *skb)
 {
     skb->secmark = 0;
 }
 #else
 static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
 { }
 
 static inline void skb_init_secmark(struct sk_buff *skb)
 { }
 #endif
 
 static inline int secpath_exists(const struct sk_buff *skb)
 {
 #ifdef CONFIG_XFRM
     return skb_ext_exist(skb, SKB_EXT_SEC_PATH);
 #else
     return 0;
 #endif
 }
 
 static inline bool skb_irq_freeable(const struct sk_buff *skb)
 {
     return !skb->destructor &&
         !secpath_exists(skb) &&
         !skb_nfct(skb) &&
         !skb->_skb_refdst &&
         !skb_has_frag_list(skb);
 }
 
 static inline void skb_set_queue_mapping(struct sk_buff *skb, u16 queue_mapping)
 {
     skb->queue_mapping = queue_mapping;
 }
 
 static inline u16 skb_get_queue_mapping(const struct sk_buff *skb)
 {
     return skb->queue_mapping;
 }
 
 static inline void skb_copy_queue_mapping(struct sk_buff *to, const struct sk_buff *from)
 {
     to->queue_mapping = from->queue_mapping;
 }
 
 static inline void skb_record_rx_queue(struct sk_buff *skb, u16 rx_queue)
 {
     skb->queue_mapping = rx_queue + 1;
 }
 
 static inline u16 skb_get_rx_queue(const struct sk_buff *skb)
 {
     return skb->queue_mapping - 1;
 }
 
 static inline bool skb_rx_queue_recorded(const struct sk_buff *skb)
 {
     return skb->queue_mapping != 0;
 }
 
 static inline void skb_set_dst_pending_confirm(struct sk_buff *skb, u32 val)
 {
     skb->dst_pending_confirm = val;
 }
 
 static inline bool skb_get_dst_pending_confirm(const struct sk_buff *skb)
 {
     return skb->dst_pending_confirm != 0;
 }
 
 static inline struct sec_path *skb_sec_path(const struct sk_buff *skb)
 {
 #ifdef CONFIG_XFRM
     return skb_ext_find(skb, SKB_EXT_SEC_PATH);
 #else
     return NULL;
 #endif
 }
 
 /* Keeps track of mac header offset relative to skb->head.
  * It is useful for TSO of Tunneling protocol. e.g. GRE.
  * For non-tunnel skb it points to skb_mac_header() and for
  * tunnel skb it points to outer mac header.
  * Keeps track of level of encapsulation of network headers.
  */
 struct skb_gso_cb {
     union {
         int mac_offset;
         int data_offset;
     };
     int encap_level;
     __wsum  csum;
     __u16   csum_start;
 };
 #define SKB_GSO_CB_OFFSET   32
 #define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_GSO_CB_OFFSET))
 
 static inline int skb_tnl_header_len(const struct sk_buff *inner_skb)
 {
     return (skb_mac_header(inner_skb) - inner_skb->head) -
         SKB_GSO_CB(inner_skb)->mac_offset;
 }
 
 static inline int gso_pskb_expand_head(struct sk_buff *skb, int extra)
 {
     int new_headroom, headroom;
     int ret;
 
     headroom = skb_headroom(skb);
     ret = pskb_expand_head(skb, extra, 0, GFP_ATOMIC);
     if (ret)
         return ret;
 
     new_headroom = skb_headroom(skb);
     SKB_GSO_CB(skb)->mac_offset += (new_headroom - headroom);
     return 0;
 }
 
 static inline void gso_reset_checksum(struct sk_buff *skb, __wsum res)
 {
     /* Do not update partial checksums if remote checksum is enabled. */
     if (skb->remcsum_offload)
         return;
 
     SKB_GSO_CB(skb)->csum = res;
     SKB_GSO_CB(skb)->csum_start = skb_checksum_start(skb) - skb->head;
 }
 
 /* Compute the checksum for a gso segment. First compute the checksum value
  * from the start of transport header to SKB_GSO_CB(skb)->csum_start, and
  * then add in skb->csum (checksum from csum_start to end of packet).
  * skb->csum and csum_start are then updated to reflect the checksum of the
  * resultant packet starting from the transport header-- the resultant checksum
  * is in the res argument (i.e. normally zero or ~ of checksum of a pseudo
  * header.
  */
 static inline __sum16 gso_make_checksum(struct sk_buff *skb, __wsum res)
 {
     unsigned char *csum_start = skb_transport_header(skb);
     int plen = (skb->head + SKB_GSO_CB(skb)->csum_start) - csum_start;
     __wsum partial = SKB_GSO_CB(skb)->csum;
 
     SKB_GSO_CB(skb)->csum = res;
     SKB_GSO_CB(skb)->csum_start = csum_start - skb->head;
 
     return csum_fold(csum_partial(csum_start, plen, partial));
 }
 
 static inline bool skb_is_gso(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->gso_size;
 }
 
 /* Note: Should be called only if skb_is_gso(skb) is true */
 static inline bool skb_is_gso_v6(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
 }
 
 /* Note: Should be called only if skb_is_gso(skb) is true */
 static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
 }
 
 /* Note: Should be called only if skb_is_gso(skb) is true */
 static inline bool skb_is_gso_tcp(const struct sk_buff *skb)
 {
     return skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6);
 }
 
 static inline void skb_gso_reset(struct sk_buff *skb)
 {
     skb_shinfo(skb)->gso_size = 0;
     skb_shinfo(skb)->gso_segs = 0;
     skb_shinfo(skb)->gso_type = 0;
 }
 
 static inline void skb_increase_gso_size(struct skb_shared_info *shinfo,
                      u16 increment)
 {
     if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
         return;
     shinfo->gso_size += increment;
 }
 
 static inline void skb_decrease_gso_size(struct skb_shared_info *shinfo,
                      u16 decrement)
 {
     if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
         return;
     shinfo->gso_size -= decrement;
 }
 
 void __skb_warn_lro_forwarding(const struct sk_buff *skb);
 
 static inline bool skb_warn_if_lro(const struct sk_buff *skb)
 {
     /* LRO sets gso_size but not gso_type, whereas if GSO is really
      * wanted then gso_type will be set. */
     const struct skb_shared_info *shinfo = skb_shinfo(skb);
 
     if (skb_is_nonlinear(skb) && shinfo->gso_size != 0 &&
         unlikely(shinfo->gso_type == 0)) {
         __skb_warn_lro_forwarding(skb);
         return true;
     }
     return false;
 }
 
 static inline void skb_forward_csum(struct sk_buff *skb)
 {
     /* Unfortunately we don't support this one.  Any brave souls? */
     if (skb->ip_summed == CHECKSUM_COMPLETE)
         skb->ip_summed = CHECKSUM_NONE;
 }
 
 /**
  * skb_checksum_none_assert - make sure skb ip_summed is CHECKSUM_NONE
  * @skb: skb to check
  *
  * fresh skbs have their ip_summed set to CHECKSUM_NONE.
  * Instead of forcing ip_summed to CHECKSUM_NONE, we can
  * use this helper, to document places where we make this assertion.
  */
 static inline void skb_checksum_none_assert(const struct sk_buff *skb)
 {
     DEBUG_NET_WARN_ON_ONCE(skb->ip_summed != CHECKSUM_NONE);
 }
 
 bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
 
 int skb_checksum_setup(struct sk_buff *skb, bool recalculate);
 struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
                      unsigned int transport_len,
                      __sum16(*skb_chkf)(struct sk_buff *skb));
 
 /**
  * skb_head_is_locked - Determine if the skb->head is locked down
  * @skb: skb to check
  *
  * The head on skbs build around a head frag can be removed if they are
  * not cloned.  This function returns true if the skb head is locked down
  * due to either being allocated via kmalloc, or by being a clone with
  * multiple references to the head.
  */
 static inline bool skb_head_is_locked(const struct sk_buff *skb)
 {
     return !skb->head_frag || skb_cloned(skb);
 }
 
 /* Local Checksum Offload.
  * Compute outer checksum based on the assumption that the
  * inner checksum will be offloaded later.
  * See Documentation/networking/checksum-offloads.rst for
  * explanation of how this works.
  * Fill in outer checksum adjustment (e.g. with sum of outer
  * pseudo-header) before calling.
  * Also ensure that inner checksum is in linear data area.
  */
 static inline __wsum lco_csum(struct sk_buff *skb)
 {
     unsigned char *csum_start = skb_checksum_start(skb);
     unsigned char *l4_hdr = skb_transport_header(skb);
     __wsum partial;
 
     /* Start with complement of inner checksum adjustment */
     partial = ~csum_unfold(*(__force __sum16 *)(csum_start +
                             skb->csum_offset));
 
     /* Add in checksum of our headers (incl. outer checksum
      * adjustment filled in by caller) and return result.
      */
     return csum_partial(l4_hdr, csum_start - l4_hdr, partial);
 }
 
 static inline bool skb_is_redirected(const struct sk_buff *skb)
 {
     return skb->redirected;
 }
 
 static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
 {
     skb->redirected = 1;
 #ifdef CONFIG_NET_REDIRECT
     skb->from_ingress = from_ingress;
     if (skb->from_ingress)
         skb_clear_tstamp(skb);
 #endif
 }
 
 static inline void skb_reset_redirect(struct sk_buff *skb)
 {
     skb->redirected = 0;
 }
 
 static inline bool skb_csum_is_sctp(struct sk_buff *skb)
 {
     return skb->csum_not_inet;
 }
 
 static inline void skb_set_kcov_handle(struct sk_buff *skb,
                        const u64 kcov_handle)
 {
 #ifdef CONFIG_KCOV
     skb->kcov_handle = kcov_handle;
 #endif
 }
 
 static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
 {
 #ifdef CONFIG_KCOV
     return skb->kcov_handle;
 #else
     return 0;
 #endif
 }
 
 #ifdef CONFIG_PAGE_POOL
 static inline void skb_mark_for_recycle(struct sk_buff *skb)
 {
     skb->pp_recycle = 1;
 }
 #endif
 
 static inline bool skb_pp_recycle(struct sk_buff *skb, void *data)
 {
     if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
         return false;
     return page_pool_return_skb_page(virt_to_page(data));
 }
 
 #endif  /* __KERNEL__ */
 #endif  /* _LINUX_SKBUFF_H */