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

 /*
  * blkfront.c
  *
  * XenLinux virtual block device driver.
  *
  * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
  * Modifications by Mark A. Williamson are (c) Intel Research Cambridge
  * Copyright (c) 2004, Christian Limpach
  * Copyright (c) 2004, Andrew Warfield
  * Copyright (c) 2005, Christopher Clark
  * Copyright (c) 2005, XenSource Ltd
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2
  * as published by the Free Software Foundation; or, when distributed
  * separately from the Linux kernel or incorporated into other
  * software packages, subject to the following license:
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this source file (the "Software"), to deal in the Software without
  * restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
  * and to permit persons to whom the Software is furnished to do so, subject to
  * the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */
 
 #include <linux/interrupt.h>
 #include <linux/blkdev.h>
 #include <linux/blk-mq.h>
 #include <linux/hdreg.h>
 #include <linux/cdrom.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/major.h>
 #include <linux/mutex.h>
 #include <linux/scatterlist.h>
 #include <linux/bitmap.h>
 #include <linux/list.h>
 #include <linux/workqueue.h>
 #include <linux/sched/mm.h>
 
 #include <xen/xen.h>
 #include <xen/xenbus.h>
 #include <xen/grant_table.h>
 #include <xen/events.h>
 #include <xen/page.h>
 #include <xen/platform_pci.h>
 
 #include <xen/interface/grant_table.h>
 #include <xen/interface/io/blkif.h>
 #include <xen/interface/io/protocols.h>
 
 #include <asm/xen/hypervisor.h>
 
 /*
  * The minimal size of segment supported by the block framework is PAGE_SIZE.
  * When Linux is using a different page size than Xen, it may not be possible
  * to put all the data in a single segment.
  * This can happen when the backend doesn't support indirect descriptor and
  * therefore the maximum amount of data that a request can carry is
  * BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE = 44KB
  *
  * Note that we only support one extra request. So the Linux page size
  * should be <= ( 2 * BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE) =
  * 88KB.
  */
 #define HAS_EXTRA_REQ (BLKIF_MAX_SEGMENTS_PER_REQUEST < XEN_PFN_PER_PAGE)
 
 enum blkif_state {
     BLKIF_STATE_DISCONNECTED,
     BLKIF_STATE_CONNECTED,
     BLKIF_STATE_SUSPENDED,
     BLKIF_STATE_ERROR,
 };
 
 struct grant {
     grant_ref_t gref;
     struct page *page;
     struct list_head node;
 };
 
 enum blk_req_status {
     REQ_PROCESSING,
     REQ_WAITING,
     REQ_DONE,
     REQ_ERROR,
     REQ_EOPNOTSUPP,
 };
 
 struct blk_shadow {
     struct blkif_request req;
     struct request *request;
     struct grant **grants_used;
     struct grant **indirect_grants;
     struct scatterlist *sg;
     unsigned int num_sg;
     enum blk_req_status status;
 
     #define NO_ASSOCIATED_ID ~0UL
     /*
      * Id of the sibling if we ever need 2 requests when handling a
      * block I/O request
      */
     unsigned long associated_id;
 };
 
 struct blkif_req {
     blk_status_t    error;
 };
 
 static inline struct blkif_req *blkif_req(struct request *rq)
 {
     return blk_mq_rq_to_pdu(rq);
 }
 
 static DEFINE_MUTEX(blkfront_mutex);
 static const struct block_device_operations xlvbd_block_fops;
 static struct delayed_work blkfront_work;
 static LIST_HEAD(info_list);
 
 /*
  * Maximum number of segments in indirect requests, the actual value used by
  * the frontend driver is the minimum of this value and the value provided
  * by the backend driver.
  */
 
 static unsigned int xen_blkif_max_segments = 32;
 module_param_named(max_indirect_segments, xen_blkif_max_segments, uint, 0444);
 MODULE_PARM_DESC(max_indirect_segments,
          "Maximum amount of segments in indirect requests (default is 32)");
 
 static unsigned int xen_blkif_max_queues = 4;
 module_param_named(max_queues, xen_blkif_max_queues, uint, 0444);
 MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues/rings used per virtual disk");
 
 /*
  * Maximum order of pages to be used for the shared ring between front and
  * backend, 4KB page granularity is used.
  */
 static unsigned int xen_blkif_max_ring_order;
 module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, 0444);
 MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");
 
 static bool __read_mostly xen_blkif_trusted = true;
 module_param_named(trusted, xen_blkif_trusted, bool, 0644);
 MODULE_PARM_DESC(trusted, "Is the backend trusted");
 
 #define BLK_RING_SIZE(info) \
     __CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * (info)->nr_ring_pages)
 
 /*
  * ring-ref%u i=(-1UL) would take 11 characters + 'ring-ref' is 8, so 19
  * characters are enough. Define to 20 to keep consistent with backend.
  */
 #define RINGREF_NAME_LEN (20)
 /*
  * queue-%u would take 7 + 10(UINT_MAX) = 17 characters.
  */
 #define QUEUE_NAME_LEN (17)
 
 /*
  *  Per-ring info.
  *  Every blkfront device can associate with one or more blkfront_ring_info,
  *  depending on how many hardware queues/rings to be used.
  */
 struct blkfront_ring_info {
     /* Lock to protect data in every ring buffer. */
     spinlock_t ring_lock;
     struct blkif_front_ring ring;
     unsigned int ring_ref[XENBUS_MAX_RING_GRANTS];
     unsigned int evtchn, irq;
     struct work_struct work;
     struct gnttab_free_callback callback;
     struct list_head indirect_pages;
     struct list_head grants;
     unsigned int persistent_gnts_c;
     unsigned long shadow_free;
     struct blkfront_info *dev_info;
     struct blk_shadow shadow[];
 };
 
 /*
  * We have one of these per vbd, whether ide, scsi or 'other'.  They
  * hang in private_data off the gendisk structure. We may end up
  * putting all kinds of interesting stuff here :-)
  */
 struct blkfront_info
 {
     struct mutex mutex;
     struct xenbus_device *xbdev;
     struct gendisk *gd;
     u16 sector_size;
     unsigned int physical_sector_size;
     unsigned long vdisk_info;
     int vdevice;
     blkif_vdev_t handle;
     enum blkif_state connected;
     /* Number of pages per ring buffer. */
     unsigned int nr_ring_pages;
     struct request_queue *rq;
     unsigned int feature_flush:1;
     unsigned int feature_fua:1;
     unsigned int feature_discard:1;
     unsigned int feature_secdiscard:1;
     /* Connect-time cached feature_persistent parameter */
     unsigned int feature_persistent_parm:1;
     /* Persistent grants feature negotiation result */
     unsigned int feature_persistent:1;
     unsigned int bounce:1;
     unsigned int discard_granularity;
     unsigned int discard_alignment;
     /* Number of 4KB segments handled */
     unsigned int max_indirect_segments;
     int is_ready;
     struct blk_mq_tag_set tag_set;
     struct blkfront_ring_info *rinfo;
     unsigned int nr_rings;
     unsigned int rinfo_size;
     /* Save uncomplete reqs and bios for migration. */
     struct list_head requests;
     struct bio_list bio_list;
     struct list_head info_list;
 };
 
 static unsigned int nr_minors;
 static unsigned long *minors;
 static DEFINE_SPINLOCK(minor_lock);
 
 #define PARTS_PER_DISK      16
 #define PARTS_PER_EXT_DISK      256
 
 #define BLKIF_MAJOR(dev) ((dev)>>8)
 #define BLKIF_MINOR(dev) ((dev) & 0xff)
 
 #define EXT_SHIFT 28
 #define EXTENDED (1<<EXT_SHIFT)
 #define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
 #define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
 #define EMULATED_HD_DISK_MINOR_OFFSET (0)
 #define EMULATED_HD_DISK_NAME_OFFSET (EMULATED_HD_DISK_MINOR_OFFSET / 256)
 #define EMULATED_SD_DISK_MINOR_OFFSET (0)
 #define EMULATED_SD_DISK_NAME_OFFSET (EMULATED_SD_DISK_MINOR_OFFSET / 256)
 
 #define DEV_NAME    "xvd"   /* name in /dev */
 
 /*
  * Grants are always the same size as a Xen page (i.e 4KB).
  * A physical segment is always the same size as a Linux page.
  * Number of grants per physical segment
  */
 #define GRANTS_PER_PSEG (PAGE_SIZE / XEN_PAGE_SIZE)
 
 #define GRANTS_PER_INDIRECT_FRAME \
     (XEN_PAGE_SIZE / sizeof(struct blkif_request_segment))
 
 #define INDIRECT_GREFS(_grants)     \
     DIV_ROUND_UP(_grants, GRANTS_PER_INDIRECT_FRAME)
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo);
 static void blkfront_gather_backend_features(struct blkfront_info *info);
 static int negotiate_mq(struct blkfront_info *info);
 
 #define for_each_rinfo(info, ptr, idx)              \
     for ((ptr) = (info)->rinfo, (idx) = 0;          \
          (idx) < (info)->nr_rings;              \
          (idx)++, (ptr) = (void *)(ptr) + (info)->rinfo_size)
 
 static inline struct blkfront_ring_info *
 get_rinfo(const struct blkfront_info *info, unsigned int i)
 {
     BUG_ON(i >= info->nr_rings);
     return (void *)info->rinfo + i * info->rinfo_size;
 }
 
 static int get_id_from_freelist(struct blkfront_ring_info *rinfo)
 {
     unsigned long free = rinfo->shadow_free;
 
     BUG_ON(free >= BLK_RING_SIZE(rinfo->dev_info));
     rinfo->shadow_free = rinfo->shadow[free].req.u.rw.id;
     rinfo->shadow[free].req.u.rw.id = 0x0fffffee; /* debug */
     return free;
 }
 
 static int add_id_to_freelist(struct blkfront_ring_info *rinfo,
                   unsigned long id)
 {
     if (rinfo->shadow[id].req.u.rw.id != id)
         return -EINVAL;
     if (rinfo->shadow[id].request == NULL)
         return -EINVAL;
     rinfo->shadow[id].req.u.rw.id  = rinfo->shadow_free;
     rinfo->shadow[id].request = NULL;
     rinfo->shadow_free = id;
     return 0;
 }
 
 static int fill_grant_buffer(struct blkfront_ring_info *rinfo, int num)
 {
     struct blkfront_info *info = rinfo->dev_info;
     struct page *granted_page;
     struct grant *gnt_list_entry, *n;
     int i = 0;
 
     while (i < num) {
         gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
         if (!gnt_list_entry)
             goto out_of_memory;
 
         if (info->bounce) {
             granted_page = alloc_page(GFP_NOIO | __GFP_ZERO);
             if (!granted_page) {
                 kfree(gnt_list_entry);
                 goto out_of_memory;
             }
             gnt_list_entry->page = granted_page;
         }
 
         gnt_list_entry->gref = INVALID_GRANT_REF;
         list_add(&gnt_list_entry->node, &rinfo->grants);
         i++;
     }
 
     return 0;
 
 out_of_memory:
     list_for_each_entry_safe(gnt_list_entry, n,
                              &rinfo->grants, node) {
         list_del(&gnt_list_entry->node);
         if (info->bounce)
             __free_page(gnt_list_entry->page);
         kfree(gnt_list_entry);
         i--;
     }
     BUG_ON(i != 0);
     return -ENOMEM;
 }
 
 static struct grant *get_free_grant(struct blkfront_ring_info *rinfo)
 {
     struct grant *gnt_list_entry;
 
     BUG_ON(list_empty(&rinfo->grants));
     gnt_list_entry = list_first_entry(&rinfo->grants, struct grant,
                       node);
     list_del(&gnt_list_entry->node);
 
     if (gnt_list_entry->gref != INVALID_GRANT_REF)
         rinfo->persistent_gnts_c--;
 
     return gnt_list_entry;
 }
 
 static inline void grant_foreign_access(const struct grant *gnt_list_entry,
                     const struct blkfront_info *info)
 {
     gnttab_page_grant_foreign_access_ref_one(gnt_list_entry->gref,
                          info->xbdev->otherend_id,
                          gnt_list_entry->page,
                          0);
 }
 
 static struct grant *get_grant(grant_ref_t *gref_head,
                    unsigned long gfn,
                    struct blkfront_ring_info *rinfo)
 {
     struct grant *gnt_list_entry = get_free_grant(rinfo);
     struct blkfront_info *info = rinfo->dev_info;
 
     if (gnt_list_entry->gref != INVALID_GRANT_REF)
         return gnt_list_entry;
 
     /* Assign a gref to this page */
     gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
     BUG_ON(gnt_list_entry->gref == -ENOSPC);
     if (info->bounce)
         grant_foreign_access(gnt_list_entry, info);
     else {
         /* Grant access to the GFN passed by the caller */
         gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
                         info->xbdev->otherend_id,
                         gfn, 0);
     }
 
     return gnt_list_entry;
 }
 
 static struct grant *get_indirect_grant(grant_ref_t *gref_head,
                     struct blkfront_ring_info *rinfo)
 {
     struct grant *gnt_list_entry = get_free_grant(rinfo);
     struct blkfront_info *info = rinfo->dev_info;
 
     if (gnt_list_entry->gref != INVALID_GRANT_REF)
         return gnt_list_entry;
 
     /* Assign a gref to this page */
     gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
     BUG_ON(gnt_list_entry->gref == -ENOSPC);
     if (!info->bounce) {
         struct page *indirect_page;
 
         /* Fetch a pre-allocated page to use for indirect grefs */
         BUG_ON(list_empty(&rinfo->indirect_pages));
         indirect_page = list_first_entry(&rinfo->indirect_pages,
                          struct page, lru);
         list_del(&indirect_page->lru);
         gnt_list_entry->page = indirect_page;
     }
     grant_foreign_access(gnt_list_entry, info);
 
     return gnt_list_entry;
 }
 
 static const char *op_name(int op)
 {
     static const char *const names[] = {
         [BLKIF_OP_READ] = "read",
         [BLKIF_OP_WRITE] = "write",
         [BLKIF_OP_WRITE_BARRIER] = "barrier",
         [BLKIF_OP_FLUSH_DISKCACHE] = "flush",
         [BLKIF_OP_DISCARD] = "discard" };
 
     if (op < 0 || op >= ARRAY_SIZE(names))
         return "unknown";
 
     if (!names[op])
         return "reserved";
 
     return names[op];
 }
 static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
 {
     unsigned int end = minor + nr;
     int rc;
 
     if (end > nr_minors) {
         unsigned long *bitmap, *old;
 
         bitmap = kcalloc(BITS_TO_LONGS(end), sizeof(*bitmap),
                  GFP_KERNEL);
         if (bitmap == NULL)
             return -ENOMEM;
 
         spin_lock(&minor_lock);
         if (end > nr_minors) {
             old = minors;
             memcpy(bitmap, minors,
                    BITS_TO_LONGS(nr_minors) * sizeof(*bitmap));
             minors = bitmap;
             nr_minors = BITS_TO_LONGS(end) * BITS_PER_LONG;
         } else
             old = bitmap;
         spin_unlock(&minor_lock);
         kfree(old);
     }
 
     spin_lock(&minor_lock);
     if (find_next_bit(minors, end, minor) >= end) {
         bitmap_set(minors, minor, nr);
         rc = 0;
     } else
         rc = -EBUSY;
     spin_unlock(&minor_lock);
 
     return rc;
 }
 
 static void xlbd_release_minors(unsigned int minor, unsigned int nr)
 {
     unsigned int end = minor + nr;
 
     BUG_ON(end > nr_minors);
     spin_lock(&minor_lock);
     bitmap_clear(minors,  minor, nr);
     spin_unlock(&minor_lock);
 }
 
 static void blkif_restart_queue_callback(void *arg)
 {
     struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)arg;
     schedule_work(&rinfo->work);
 }
 
 static int blkif_getgeo(struct block_device *bd, struct hd_geometry *hg)
 {
     /* We don't have real geometry info, but let's at least return
        values consistent with the size of the device */
     sector_t nsect = get_capacity(bd->bd_disk);
     sector_t cylinders = nsect;
 
     hg->heads = 0xff;
     hg->sectors = 0x3f;
     sector_div(cylinders, hg->heads * hg->sectors);
     hg->cylinders = cylinders;
     if ((sector_t)(hg->cylinders + 1) * hg->heads * hg->sectors < nsect)
         hg->cylinders = 0xffff;
     return 0;
 }
 
 static int blkif_ioctl(struct block_device *bdev, fmode_t mode,
                unsigned command, unsigned long argument)
 {
     struct blkfront_info *info = bdev->bd_disk->private_data;
     int i;
 
     switch (command) {
     case CDROMMULTISESSION:
         for (i = 0; i < sizeof(struct cdrom_multisession); i++)
             if (put_user(0, (char __user *)(argument + i)))
                 return -EFAULT;
         return 0;
     case CDROM_GET_CAPABILITY:
         if (!(info->vdisk_info & VDISK_CDROM))
             return -EINVAL;
         return 0;
     default:
         return -EINVAL;
     }
 }
 
 static unsigned long blkif_ring_get_request(struct blkfront_ring_info *rinfo,
                         struct request *req,
                         struct blkif_request **ring_req)
 {
     unsigned long id;
 
     *ring_req = RING_GET_REQUEST(&rinfo->ring, rinfo->ring.req_prod_pvt);
     rinfo->ring.req_prod_pvt++;
 
     id = get_id_from_freelist(rinfo);
     rinfo->shadow[id].request = req;
     rinfo->shadow[id].status = REQ_PROCESSING;
     rinfo->shadow[id].associated_id = NO_ASSOCIATED_ID;
 
     rinfo->shadow[id].req.u.rw.id = id;
 
     return id;
 }
 
 static int blkif_queue_discard_req(struct request *req, struct blkfront_ring_info *rinfo)
 {
     struct blkfront_info *info = rinfo->dev_info;
     struct blkif_request *ring_req, *final_ring_req;
     unsigned long id;
 
     /* Fill out a communications ring structure. */
     id = blkif_ring_get_request(rinfo, req, &final_ring_req);
     ring_req = &rinfo->shadow[id].req;
 
     ring_req->operation = BLKIF_OP_DISCARD;
     ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
     ring_req->u.discard.id = id;
     ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
     if (req_op(req) == REQ_OP_SECURE_ERASE && info->feature_secdiscard)
         ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
     else
         ring_req->u.discard.flag = 0;
 
     /* Copy the request to the ring page. */
     *final_ring_req = *ring_req;
     rinfo->shadow[id].status = REQ_WAITING;
 
     return 0;
 }
 
 struct setup_rw_req {
     unsigned int grant_idx;
     struct blkif_request_segment *segments;
     struct blkfront_ring_info *rinfo;
     struct blkif_request *ring_req;
     grant_ref_t gref_head;
     unsigned int id;
     /* Only used when persistent grant is used and it's a write request */
     bool need_copy;
     unsigned int bvec_off;
     char *bvec_data;
 
     bool require_extra_req;
     struct blkif_request *extra_ring_req;
 };
 
 static void blkif_setup_rw_req_grant(unsigned long gfn, unsigned int offset,
                      unsigned int len, void *data)
 {
     struct setup_rw_req *setup = data;
     int n, ref;
     struct grant *gnt_list_entry;
     unsigned int fsect, lsect;
     /* Convenient aliases */
     unsigned int grant_idx = setup->grant_idx;
     struct blkif_request *ring_req = setup->ring_req;
     struct blkfront_ring_info *rinfo = setup->rinfo;
     /*
      * We always use the shadow of the first request to store the list
      * of grant associated to the block I/O request. This made the
      * completion more easy to handle even if the block I/O request is
      * split.
      */
     struct blk_shadow *shadow = &rinfo->shadow[setup->id];
 
     if (unlikely(setup->require_extra_req &&
              grant_idx >= BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
         /*
          * We are using the second request, setup grant_idx
          * to be the index of the segment array.
          */
         grant_idx -= BLKIF_MAX_SEGMENTS_PER_REQUEST;
         ring_req = setup->extra_ring_req;
     }
 
     if ((ring_req->operation == BLKIF_OP_INDIRECT) &&
         (grant_idx % GRANTS_PER_INDIRECT_FRAME == 0)) {
         if (setup->segments)
             kunmap_atomic(setup->segments);
 
         n = grant_idx / GRANTS_PER_INDIRECT_FRAME;
         gnt_list_entry = get_indirect_grant(&setup->gref_head, rinfo);
         shadow->indirect_grants[n] = gnt_list_entry;
         setup->segments = kmap_atomic(gnt_list_entry->page);
         ring_req->u.indirect.indirect_grefs[n] = gnt_list_entry->gref;
     }
 
     gnt_list_entry = get_grant(&setup->gref_head, gfn, rinfo);
     ref = gnt_list_entry->gref;
     /*
      * All the grants are stored in the shadow of the first
      * request. Therefore we have to use the global index.
      */
     shadow->grants_used[setup->grant_idx] = gnt_list_entry;
 
     if (setup->need_copy) {
         void *shared_data;
 
         shared_data = kmap_atomic(gnt_list_entry->page);
         /*
          * this does not wipe data stored outside the
          * range sg->offset..sg->offset+sg->length.
          * Therefore, blkback *could* see data from
          * previous requests. This is OK as long as
          * persistent grants are shared with just one
          * domain. It may need refactoring if this
          * changes
          */
         memcpy(shared_data + offset,
                setup->bvec_data + setup->bvec_off,
                len);
 
         kunmap_atomic(shared_data);
         setup->bvec_off += len;
     }
 
     fsect = offset >> 9;
     lsect = fsect + (len >> 9) - 1;
     if (ring_req->operation != BLKIF_OP_INDIRECT) {
         ring_req->u.rw.seg[grant_idx] =
             (struct blkif_request_segment) {
                 .gref       = ref,
                 .first_sect = fsect,
                 .last_sect  = lsect };
     } else {
         setup->segments[grant_idx % GRANTS_PER_INDIRECT_FRAME] =
             (struct blkif_request_segment) {
                 .gref       = ref,
                 .first_sect = fsect,
                 .last_sect  = lsect };
     }
 
     (setup->grant_idx)++;
 }
 
 static void blkif_setup_extra_req(struct blkif_request *first,
                   struct blkif_request *second)
 {
     uint16_t nr_segments = first->u.rw.nr_segments;
 
     /*
      * The second request is only present when the first request uses
      * all its segments. It's always the continuity of the first one.
      */
     first->u.rw.nr_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
 
     second->u.rw.nr_segments = nr_segments - BLKIF_MAX_SEGMENTS_PER_REQUEST;
     second->u.rw.sector_number = first->u.rw.sector_number +
         (BLKIF_MAX_SEGMENTS_PER_REQUEST * XEN_PAGE_SIZE) / 512;
 
     second->u.rw.handle = first->u.rw.handle;
     second->operation = first->operation;
 }
 
 static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *rinfo)
 {
     struct blkfront_info *info = rinfo->dev_info;
     struct blkif_request *ring_req, *extra_ring_req = NULL;
     struct blkif_request *final_ring_req, *final_extra_ring_req = NULL;
     unsigned long id, extra_id = NO_ASSOCIATED_ID;
     bool require_extra_req = false;
     int i;
     struct setup_rw_req setup = {
         .grant_idx = 0,
         .segments = NULL,
         .rinfo = rinfo,
         .need_copy = rq_data_dir(req) && info->bounce,
     };
 
     /*
      * Used to store if we are able to queue the request by just using
      * existing persistent grants, or if we have to get new grants,
      * as there are not sufficiently many free.
      */
     bool new_persistent_gnts = false;
     struct scatterlist *sg;
     int num_sg, max_grefs, num_grant;
 
     max_grefs = req->nr_phys_segments * GRANTS_PER_PSEG;
     if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
         /*
          * If we are using indirect segments we need to account
          * for the indirect grefs used in the request.
          */
         max_grefs += INDIRECT_GREFS(max_grefs);
 
     /* Check if we have enough persistent grants to allocate a requests */
     if (rinfo->persistent_gnts_c < max_grefs) {
         new_persistent_gnts = true;
 
         if (gnttab_alloc_grant_references(
             max_grefs - rinfo->persistent_gnts_c,
             &setup.gref_head) < 0) {
             gnttab_request_free_callback(
                 &rinfo->callback,
                 blkif_restart_queue_callback,
                 rinfo,
                 max_grefs - rinfo->persistent_gnts_c);
             return 1;
         }
     }
 
     /* Fill out a communications ring structure. */
     id = blkif_ring_get_request(rinfo, req, &final_ring_req);
     ring_req = &rinfo->shadow[id].req;
 
     num_sg = blk_rq_map_sg(req->q, req, rinfo->shadow[id].sg);
     num_grant = 0;
     /* Calculate the number of grant used */
     for_each_sg(rinfo->shadow[id].sg, sg, num_sg, i)
            num_grant += gnttab_count_grant(sg->offset, sg->length);
 
     require_extra_req = info->max_indirect_segments == 0 &&
         num_grant > BLKIF_MAX_SEGMENTS_PER_REQUEST;
     BUG_ON(!HAS_EXTRA_REQ && require_extra_req);
 
     rinfo->shadow[id].num_sg = num_sg;
     if (num_grant > BLKIF_MAX_SEGMENTS_PER_REQUEST &&
         likely(!require_extra_req)) {
         /*
          * The indirect operation can only be a BLKIF_OP_READ or
          * BLKIF_OP_WRITE
          */
         BUG_ON(req_op(req) == REQ_OP_FLUSH || req->cmd_flags & REQ_FUA);
         ring_req->operation = BLKIF_OP_INDIRECT;
         ring_req->u.indirect.indirect_op = rq_data_dir(req) ?
             BLKIF_OP_WRITE : BLKIF_OP_READ;
         ring_req->u.indirect.sector_number = (blkif_sector_t)blk_rq_pos(req);
         ring_req->u.indirect.handle = info->handle;
         ring_req->u.indirect.nr_segments = num_grant;
     } else {
         ring_req->u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
         ring_req->u.rw.handle = info->handle;
         ring_req->operation = rq_data_dir(req) ?
             BLKIF_OP_WRITE : BLKIF_OP_READ;
         if (req_op(req) == REQ_OP_FLUSH || req->cmd_flags & REQ_FUA) {
             /*
              * Ideally we can do an unordered flush-to-disk.
              * In case the backend onlysupports barriers, use that.
              * A barrier request a superset of FUA, so we can
              * implement it the same way.  (It's also a FLUSH+FUA,
              * since it is guaranteed ordered WRT previous writes.)
              */
             if (info->feature_flush && info->feature_fua)
                 ring_req->operation =
                     BLKIF_OP_WRITE_BARRIER;
             else if (info->feature_flush)
                 ring_req->operation =
                     BLKIF_OP_FLUSH_DISKCACHE;
             else
                 ring_req->operation = 0;
         }
         ring_req->u.rw.nr_segments = num_grant;
         if (unlikely(require_extra_req)) {
             extra_id = blkif_ring_get_request(rinfo, req,
                               &final_extra_ring_req);
             extra_ring_req = &rinfo->shadow[extra_id].req;
 
             /*
              * Only the first request contains the scatter-gather
              * list.
              */
             rinfo->shadow[extra_id].num_sg = 0;
 
             blkif_setup_extra_req(ring_req, extra_ring_req);
 
             /* Link the 2 requests together */
             rinfo->shadow[extra_id].associated_id = id;
             rinfo->shadow[id].associated_id = extra_id;
         }
     }
 
     setup.ring_req = ring_req;
     setup.id = id;
 
     setup.require_extra_req = require_extra_req;
     if (unlikely(require_extra_req))
         setup.extra_ring_req = extra_ring_req;
 
     for_each_sg(rinfo->shadow[id].sg, sg, num_sg, i) {
         BUG_ON(sg->offset + sg->length > PAGE_SIZE);
 
         if (setup.need_copy) {
             setup.bvec_off = sg->offset;
             setup.bvec_data = kmap_atomic(sg_page(sg));
         }
 
         gnttab_foreach_grant_in_range(sg_page(sg),
                           sg->offset,
                           sg->length,
                           blkif_setup_rw_req_grant,
                           &setup);
 
         if (setup.need_copy)
             kunmap_atomic(setup.bvec_data);
     }
     if (setup.segments)
         kunmap_atomic(setup.segments);
 
     /* Copy request(s) to the ring page. */
     *final_ring_req = *ring_req;
     rinfo->shadow[id].status = REQ_WAITING;
     if (unlikely(require_extra_req)) {
         *final_extra_ring_req = *extra_ring_req;
         rinfo->shadow[extra_id].status = REQ_WAITING;
     }
 
     if (new_persistent_gnts)
         gnttab_free_grant_references(setup.gref_head);
 
     return 0;
 }
 
 /*
  * Generate a Xen blkfront IO request from a blk layer request.  Reads
  * and writes are handled as expected.
  *
  * @req: a request struct
  */
 static int blkif_queue_request(struct request *req, struct blkfront_ring_info *rinfo)
 {
     if (unlikely(rinfo->dev_info->connected != BLKIF_STATE_CONNECTED))
         return 1;
 
     if (unlikely(req_op(req) == REQ_OP_DISCARD ||
              req_op(req) == REQ_OP_SECURE_ERASE))
         return blkif_queue_discard_req(req, rinfo);
     else
         return blkif_queue_rw_req(req, rinfo);
 }
 
 static inline void flush_requests(struct blkfront_ring_info *rinfo)
 {
     int notify;
 
     RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&rinfo->ring, notify);
 
     if (notify)
         notify_remote_via_irq(rinfo->irq);
 }
 
 static inline bool blkif_request_flush_invalid(struct request *req,
                            struct blkfront_info *info)
 {
     return (blk_rq_is_passthrough(req) ||
         ((req_op(req) == REQ_OP_FLUSH) &&
          !info->feature_flush) ||
         ((req->cmd_flags & REQ_FUA) &&
          !info->feature_fua));
 }
 
 static blk_status_t blkif_queue_rq(struct blk_mq_hw_ctx *hctx,
               const struct blk_mq_queue_data *qd)
 {
     unsigned long flags;
     int qid = hctx->queue_num;
     struct blkfront_info *info = hctx->queue->queuedata;
     struct blkfront_ring_info *rinfo = NULL;
 
     rinfo = get_rinfo(info, qid);
     blk_mq_start_request(qd->rq);
     spin_lock_irqsave(&rinfo->ring_lock, flags);
     if (RING_FULL(&rinfo->ring))
         goto out_busy;
 
     if (blkif_request_flush_invalid(qd->rq, rinfo->dev_info))
         goto out_err;
 
     if (blkif_queue_request(qd->rq, rinfo))
         goto out_busy;
 
     flush_requests(rinfo);
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
     return BLK_STS_OK;
 
 out_err:
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
     return BLK_STS_IOERR;
 
 out_busy:
     blk_mq_stop_hw_queue(hctx);
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
     return BLK_STS_DEV_RESOURCE;
 }
 
 static void blkif_complete_rq(struct request *rq)
 {
     blk_mq_end_request(rq, blkif_req(rq)->error);
 }
 
 static const struct blk_mq_ops blkfront_mq_ops = {
     .queue_rq = blkif_queue_rq,
     .complete = blkif_complete_rq,
 };
 
 static void blkif_set_queue_limits(struct blkfront_info *info)
 {
     struct request_queue *rq = info->rq;
     struct gendisk *gd = info->gd;
     unsigned int segments = info->max_indirect_segments ? :
                 BLKIF_MAX_SEGMENTS_PER_REQUEST;
 
     blk_queue_flag_set(QUEUE_FLAG_VIRT, rq);
 
     if (info->feature_discard) {
         blk_queue_max_discard_sectors(rq, get_capacity(gd));
         rq->limits.discard_granularity = info->discard_granularity ?:
                          info->physical_sector_size;
         rq->limits.discard_alignment = info->discard_alignment;
         if (info->feature_secdiscard)
             blk_queue_max_secure_erase_sectors(rq,
                                get_capacity(gd));
     }
 
     /* Hard sector size and max sectors impersonate the equiv. hardware. */
     blk_queue_logical_block_size(rq, info->sector_size);
     blk_queue_physical_block_size(rq, info->physical_sector_size);
     blk_queue_max_hw_sectors(rq, (segments * XEN_PAGE_SIZE) / 512);
 
     /* Each segment in a request is up to an aligned page in size. */
     blk_queue_segment_boundary(rq, PAGE_SIZE - 1);
     blk_queue_max_segment_size(rq, PAGE_SIZE);
 
     /* Ensure a merged request will fit in a single I/O ring slot. */
     blk_queue_max_segments(rq, segments / GRANTS_PER_PSEG);
 
     /* Make sure buffer addresses are sector-aligned. */
     blk_queue_dma_alignment(rq, 511);
 }
 
 static const char *flush_info(struct blkfront_info *info)
 {
     if (info->feature_flush && info->feature_fua)
         return "barrier: enabled;";
     else if (info->feature_flush)
         return "flush diskcache: enabled;";
     else
         return "barrier or flush: disabled;";
 }
 
 static void xlvbd_flush(struct blkfront_info *info)
 {
     blk_queue_write_cache(info->rq, info->feature_flush ? true : false,
                   info->feature_fua ? true : false);
     pr_info("blkfront: %s: %s %s %s %s %s %s %s\n",
         info->gd->disk_name, flush_info(info),
         "persistent grants:", info->feature_persistent ?
         "enabled;" : "disabled;", "indirect descriptors:",
         info->max_indirect_segments ? "enabled;" : "disabled;",
         "bounce buffer:", info->bounce ? "enabled" : "disabled;");
 }
 
 static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
 {
     int major;
     major = BLKIF_MAJOR(vdevice);
     *minor = BLKIF_MINOR(vdevice);
     switch (major) {
         case XEN_IDE0_MAJOR:
             *offset = (*minor / 64) + EMULATED_HD_DISK_NAME_OFFSET;
             *minor = ((*minor / 64) * PARTS_PER_DISK) +
                 EMULATED_HD_DISK_MINOR_OFFSET;
             break;
         case XEN_IDE1_MAJOR:
             *offset = (*minor / 64) + 2 + EMULATED_HD_DISK_NAME_OFFSET;
             *minor = (((*minor / 64) + 2) * PARTS_PER_DISK) +
                 EMULATED_HD_DISK_MINOR_OFFSET;
             break;
         case XEN_SCSI_DISK0_MAJOR:
             *offset = (*minor / PARTS_PER_DISK) + EMULATED_SD_DISK_NAME_OFFSET;
             *minor = *minor + EMULATED_SD_DISK_MINOR_OFFSET;
             break;
         case XEN_SCSI_DISK1_MAJOR:
         case XEN_SCSI_DISK2_MAJOR:
         case XEN_SCSI_DISK3_MAJOR:
         case XEN_SCSI_DISK4_MAJOR:
         case XEN_SCSI_DISK5_MAJOR:
         case XEN_SCSI_DISK6_MAJOR:
         case XEN_SCSI_DISK7_MAJOR:
             *offset = (*minor / PARTS_PER_DISK) + 
                 ((major - XEN_SCSI_DISK1_MAJOR + 1) * 16) +
                 EMULATED_SD_DISK_NAME_OFFSET;
             *minor = *minor +
                 ((major - XEN_SCSI_DISK1_MAJOR + 1) * 16 * PARTS_PER_DISK) +
                 EMULATED_SD_DISK_MINOR_OFFSET;
             break;
         case XEN_SCSI_DISK8_MAJOR:
         case XEN_SCSI_DISK9_MAJOR:
         case XEN_SCSI_DISK10_MAJOR:
         case XEN_SCSI_DISK11_MAJOR:
         case XEN_SCSI_DISK12_MAJOR:
         case XEN_SCSI_DISK13_MAJOR:
         case XEN_SCSI_DISK14_MAJOR:
         case XEN_SCSI_DISK15_MAJOR:
             *offset = (*minor / PARTS_PER_DISK) + 
                 ((major - XEN_SCSI_DISK8_MAJOR + 8) * 16) +
                 EMULATED_SD_DISK_NAME_OFFSET;
             *minor = *minor +
                 ((major - XEN_SCSI_DISK8_MAJOR + 8) * 16 * PARTS_PER_DISK) +
                 EMULATED_SD_DISK_MINOR_OFFSET;
             break;
         case XENVBD_MAJOR:
             *offset = *minor / PARTS_PER_DISK;
             break;
         default:
             printk(KERN_WARNING "blkfront: your disk configuration is "
                     "incorrect, please use an xvd device instead\n");
             return -ENODEV;
     }
     return 0;
 }
 
 static char *encode_disk_name(char *ptr, unsigned int n)
 {
     if (n >= 26)
         ptr = encode_disk_name(ptr, n / 26 - 1);
     *ptr = 'a' + n % 26;
     return ptr + 1;
 }
 
 static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
         struct blkfront_info *info, u16 sector_size,
         unsigned int physical_sector_size)
 {
     struct gendisk *gd;
     int nr_minors = 1;
     int err;
     unsigned int offset;
     int minor;
     int nr_parts;
     char *ptr;
 
     BUG_ON(info->gd != NULL);
     BUG_ON(info->rq != NULL);
 
     if ((info->vdevice>>EXT_SHIFT) > 1) {
         /* this is above the extended range; something is wrong */
         printk(KERN_WARNING "blkfront: vdevice 0x%x is above the extended range; ignoring\n", info->vdevice);
         return -ENODEV;
     }
 
     if (!VDEV_IS_EXTENDED(info->vdevice)) {
         err = xen_translate_vdev(info->vdevice, &minor, &offset);
         if (err)
             return err;
         nr_parts = PARTS_PER_DISK;
     } else {
         minor = BLKIF_MINOR_EXT(info->vdevice);
         nr_parts = PARTS_PER_EXT_DISK;
         offset = minor / nr_parts;
         if (xen_hvm_domain() && offset < EMULATED_HD_DISK_NAME_OFFSET + 4)
             printk(KERN_WARNING "blkfront: vdevice 0x%x might conflict with "
                     "emulated IDE disks,\n\t choose an xvd device name"
                     "from xvde on\n", info->vdevice);
     }
     if (minor >> MINORBITS) {
         pr_warn("blkfront: %#x's minor (%#x) out of range; ignoring\n",
             info->vdevice, minor);
         return -ENODEV;
     }
 
     if ((minor % nr_parts) == 0)
         nr_minors = nr_parts;
 
     err = xlbd_reserve_minors(minor, nr_minors);
     if (err)
         return err;
 
     memset(&info->tag_set, 0, sizeof(info->tag_set));
     info->tag_set.ops = &blkfront_mq_ops;
     info->tag_set.nr_hw_queues = info->nr_rings;
     if (HAS_EXTRA_REQ && info->max_indirect_segments == 0) {
         /*
          * When indirect descriptior is not supported, the I/O request
          * will be split between multiple request in the ring.
          * To avoid problems when sending the request, divide by
          * 2 the depth of the queue.
          */
         info->tag_set.queue_depth =  BLK_RING_SIZE(info) / 2;
     } else
         info->tag_set.queue_depth = BLK_RING_SIZE(info);
     info->tag_set.numa_node = NUMA_NO_NODE;
     info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
     info->tag_set.cmd_size = sizeof(struct blkif_req);
     info->tag_set.driver_data = info;
 
     err = blk_mq_alloc_tag_set(&info->tag_set);
     if (err)
         goto out_release_minors;
 
     gd = blk_mq_alloc_disk(&info->tag_set, info);
     if (IS_ERR(gd)) {
         err = PTR_ERR(gd);
         goto out_free_tag_set;
     }
 
     strcpy(gd->disk_name, DEV_NAME);
     ptr = encode_disk_name(gd->disk_name + sizeof(DEV_NAME) - 1, offset);
     BUG_ON(ptr >= gd->disk_name + DISK_NAME_LEN);
     if (nr_minors > 1)
         *ptr = 0;
     else
         snprintf(ptr, gd->disk_name + DISK_NAME_LEN - ptr,
              "%d", minor & (nr_parts - 1));
 
     gd->major = XENVBD_MAJOR;
     gd->first_minor = minor;
     gd->minors = nr_minors;
     gd->fops = &xlvbd_block_fops;
     gd->private_data = info;
     set_capacity(gd, capacity);
 
     info->rq = gd->queue;
     info->gd = gd;
     info->sector_size = sector_size;
     info->physical_sector_size = physical_sector_size;
     blkif_set_queue_limits(info);
 
     xlvbd_flush(info);
 
     if (info->vdisk_info & VDISK_READONLY)
         set_disk_ro(gd, 1);
     if (info->vdisk_info & VDISK_REMOVABLE)
         gd->flags |= GENHD_FL_REMOVABLE;
 
     return 0;
 
 out_free_tag_set:
     blk_mq_free_tag_set(&info->tag_set);
 out_release_minors:
     xlbd_release_minors(minor, nr_minors);
     return err;
 }
 
 /* Already hold rinfo->ring_lock. */
 static inline void kick_pending_request_queues_locked(struct blkfront_ring_info *rinfo)
 {
     if (!RING_FULL(&rinfo->ring))
         blk_mq_start_stopped_hw_queues(rinfo->dev_info->rq, true);
 }
 
 static void kick_pending_request_queues(struct blkfront_ring_info *rinfo)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&rinfo->ring_lock, flags);
     kick_pending_request_queues_locked(rinfo);
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
 }
 
 static void blkif_restart_queue(struct work_struct *work)
 {
     struct blkfront_ring_info *rinfo = container_of(work, struct blkfront_ring_info, work);
 
     if (rinfo->dev_info->connected == BLKIF_STATE_CONNECTED)
         kick_pending_request_queues(rinfo);
 }
 
 static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 {
     struct grant *persistent_gnt, *n;
     struct blkfront_info *info = rinfo->dev_info;
     int i, j, segs;
 
     /*
      * Remove indirect pages, this only happens when using indirect
      * descriptors but not persistent grants
      */
     if (!list_empty(&rinfo->indirect_pages)) {
         struct page *indirect_page, *n;
 
         BUG_ON(info->bounce);
         list_for_each_entry_safe(indirect_page, n, &rinfo->indirect_pages, lru) {
             list_del(&indirect_page->lru);
             __free_page(indirect_page);
         }
     }
 
     /* Remove all persistent grants. */
     if (!list_empty(&rinfo->grants)) {
         list_for_each_entry_safe(persistent_gnt, n,
                      &rinfo->grants, node) {
             list_del(&persistent_gnt->node);
             if (persistent_gnt->gref != INVALID_GRANT_REF) {
                 gnttab_end_foreign_access(persistent_gnt->gref,
                               NULL);
                 rinfo->persistent_gnts_c--;
             }
             if (info->bounce)
                 __free_page(persistent_gnt->page);
             kfree(persistent_gnt);
         }
     }
     BUG_ON(rinfo->persistent_gnts_c != 0);
 
     for (i = 0; i < BLK_RING_SIZE(info); i++) {
         /*
          * Clear persistent grants present in requests already
          * on the shared ring
          */
         if (!rinfo->shadow[i].request)
             goto free_shadow;
 
         segs = rinfo->shadow[i].req.operation == BLKIF_OP_INDIRECT ?
                rinfo->shadow[i].req.u.indirect.nr_segments :
                rinfo->shadow[i].req.u.rw.nr_segments;
         for (j = 0; j < segs; j++) {
             persistent_gnt = rinfo->shadow[i].grants_used[j];
             gnttab_end_foreign_access(persistent_gnt->gref, NULL);
             if (info->bounce)
                 __free_page(persistent_gnt->page);
             kfree(persistent_gnt);
         }
 
         if (rinfo->shadow[i].req.operation != BLKIF_OP_INDIRECT)
             /*
              * If this is not an indirect operation don't try to
              * free indirect segments
              */
             goto free_shadow;
 
         for (j = 0; j < INDIRECT_GREFS(segs); j++) {
             persistent_gnt = rinfo->shadow[i].indirect_grants[j];
             gnttab_end_foreign_access(persistent_gnt->gref, NULL);
             __free_page(persistent_gnt->page);
             kfree(persistent_gnt);
         }
 
 free_shadow:
         kvfree(rinfo->shadow[i].grants_used);
         rinfo->shadow[i].grants_used = NULL;
         kvfree(rinfo->shadow[i].indirect_grants);
         rinfo->shadow[i].indirect_grants = NULL;
         kvfree(rinfo->shadow[i].sg);
         rinfo->shadow[i].sg = NULL;
     }
 
     /* No more gnttab callback work. */
     gnttab_cancel_free_callback(&rinfo->callback);
 
     /* Flush gnttab callback work. Must be done with no locks held. */
     flush_work(&rinfo->work);
 
     /* Free resources associated with old device channel. */
     xenbus_teardown_ring((void **)&rinfo->ring.sring, info->nr_ring_pages,
                  rinfo->ring_ref);
 
     if (rinfo->irq)
         unbind_from_irqhandler(rinfo->irq, rinfo);
     rinfo->evtchn = rinfo->irq = 0;
 }
 
 static void blkif_free(struct blkfront_info *info, int suspend)
 {
     unsigned int i;
     struct blkfront_ring_info *rinfo;
 
     /* Prevent new requests being issued until we fix things up. */
     info->connected = suspend ?
         BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
     /* No more blkif_request(). */
     if (info->rq)
         blk_mq_stop_hw_queues(info->rq);
 
     for_each_rinfo(info, rinfo, i)
         blkif_free_ring(rinfo);
 
     kvfree(info->rinfo);
     info->rinfo = NULL;
     info->nr_rings = 0;
 }
 
 struct copy_from_grant {
     const struct blk_shadow *s;
     unsigned int grant_idx;
     unsigned int bvec_offset;
     char *bvec_data;
 };
 
 static void blkif_copy_from_grant(unsigned long gfn, unsigned int offset,
                   unsigned int len, void *data)
 {
     struct copy_from_grant *info = data;
     char *shared_data;
     /* Convenient aliases */
     const struct blk_shadow *s = info->s;
 
     shared_data = kmap_atomic(s->grants_used[info->grant_idx]->page);
 
     memcpy(info->bvec_data + info->bvec_offset,
            shared_data + offset, len);
 
     info->bvec_offset += len;
     info->grant_idx++;
 
     kunmap_atomic(shared_data);
 }
 
 static enum blk_req_status blkif_rsp_to_req_status(int rsp)
 {
     switch (rsp)
     {
     case BLKIF_RSP_OKAY:
         return REQ_DONE;
     case BLKIF_RSP_EOPNOTSUPP:
         return REQ_EOPNOTSUPP;
     case BLKIF_RSP_ERROR:
     default:
         return REQ_ERROR;
     }
 }
 
 /*
  * Get the final status of the block request based on two ring response
  */
 static int blkif_get_final_status(enum blk_req_status s1,
                   enum blk_req_status s2)
 {
     BUG_ON(s1 < REQ_DONE);
     BUG_ON(s2 < REQ_DONE);
 
     if (s1 == REQ_ERROR || s2 == REQ_ERROR)
         return BLKIF_RSP_ERROR;
     else if (s1 == REQ_EOPNOTSUPP || s2 == REQ_EOPNOTSUPP)
         return BLKIF_RSP_EOPNOTSUPP;
     return BLKIF_RSP_OKAY;
 }
 
 /*
  * Return values:
  *  1 response processed.
  *  0 missing further responses.
  * -1 error while processing.
  */
 static int blkif_completion(unsigned long *id,
                 struct blkfront_ring_info *rinfo,
                 struct blkif_response *bret)
 {
     int i = 0;
     struct scatterlist *sg;
     int num_sg, num_grant;
     struct blkfront_info *info = rinfo->dev_info;
     struct blk_shadow *s = &rinfo->shadow[*id];
     struct copy_from_grant data = {
         .grant_idx = 0,
     };
 
     num_grant = s->req.operation == BLKIF_OP_INDIRECT ?
         s->req.u.indirect.nr_segments : s->req.u.rw.nr_segments;
 
     /* The I/O request may be split in two. */
     if (unlikely(s->associated_id != NO_ASSOCIATED_ID)) {
         struct blk_shadow *s2 = &rinfo->shadow[s->associated_id];
 
         /* Keep the status of the current response in shadow. */
         s->status = blkif_rsp_to_req_status(bret->status);
 
         /* Wait the second response if not yet here. */
         if (s2->status < REQ_DONE)
             return 0;
 
         bret->status = blkif_get_final_status(s->status,
                               s2->status);
 
         /*
          * All the grants is stored in the first shadow in order
          * to make the completion code simpler.
          */
         num_grant += s2->req.u.rw.nr_segments;
 
         /*
          * The two responses may not come in order. Only the
          * first request will store the scatter-gather list.
          */
         if (s2->num_sg != 0) {
             /* Update "id" with the ID of the first response. */
             *id = s->associated_id;
             s = s2;
         }
 
         /*
          * We don't need anymore the second request, so recycling
          * it now.
          */
         if (add_id_to_freelist(rinfo, s->associated_id))
             WARN(1, "%s: can't recycle the second part (id = %ld) of the request\n",
                  info->gd->disk_name, s->associated_id);
     }
 
     data.s = s;
     num_sg = s->num_sg;
 
     if (bret->operation == BLKIF_OP_READ && info->bounce) {
         for_each_sg(s->sg, sg, num_sg, i) {
             BUG_ON(sg->offset + sg->length > PAGE_SIZE);
 
             data.bvec_offset = sg->offset;
             data.bvec_data = kmap_atomic(sg_page(sg));
 
             gnttab_foreach_grant_in_range(sg_page(sg),
                               sg->offset,
                               sg->length,
                               blkif_copy_from_grant,
                               &data);
 
             kunmap_atomic(data.bvec_data);
         }
     }
     /* Add the persistent grant into the list of free grants */
     for (i = 0; i < num_grant; i++) {
         if (!gnttab_try_end_foreign_access(s->grants_used[i]->gref)) {
             /*
              * If the grant is still mapped by the backend (the
              * backend has chosen to make this grant persistent)
              * we add it at the head of the list, so it will be
              * reused first.
              */
             if (!info->feature_persistent) {
                 pr_alert("backed has not unmapped grant: %u\n",
                      s->grants_used[i]->gref);
                 return -1;
             }
             list_add(&s->grants_used[i]->node, &rinfo->grants);
             rinfo->persistent_gnts_c++;
         } else {
             /*
              * If the grant is not mapped by the backend we add it
              * to the tail of the list, so it will not be picked
              * again unless we run out of persistent grants.
              */
             s->grants_used[i]->gref = INVALID_GRANT_REF;
             list_add_tail(&s->grants_used[i]->node, &rinfo->grants);
         }
     }
     if (s->req.operation == BLKIF_OP_INDIRECT) {
         for (i = 0; i < INDIRECT_GREFS(num_grant); i++) {
             if (!gnttab_try_end_foreign_access(s->indirect_grants[i]->gref)) {
                 if (!info->feature_persistent) {
                     pr_alert("backed has not unmapped grant: %u\n",
                          s->indirect_grants[i]->gref);
                     return -1;
                 }
                 list_add(&s->indirect_grants[i]->node, &rinfo->grants);
                 rinfo->persistent_gnts_c++;
             } else {
                 struct page *indirect_page;
 
                 /*
                  * Add the used indirect page back to the list of
                  * available pages for indirect grefs.
                  */
                 if (!info->bounce) {
                     indirect_page = s->indirect_grants[i]->page;
                     list_add(&indirect_page->lru, &rinfo->indirect_pages);
                 }
                 s->indirect_grants[i]->gref = INVALID_GRANT_REF;
                 list_add_tail(&s->indirect_grants[i]->node, &rinfo->grants);
             }
         }
     }
 
     return 1;
 }
 
 static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 {
     struct request *req;
     struct blkif_response bret;
     RING_IDX i, rp;
     unsigned long flags;
     struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)dev_id;
     struct blkfront_info *info = rinfo->dev_info;
     unsigned int eoiflag = XEN_EOI_FLAG_SPURIOUS;
 
     if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
         xen_irq_lateeoi(irq, XEN_EOI_FLAG_SPURIOUS);
         return IRQ_HANDLED;
     }
 
     spin_lock_irqsave(&rinfo->ring_lock, flags);
  again:
     rp = READ_ONCE(rinfo->ring.sring->rsp_prod);
     virt_rmb(); /* Ensure we see queued responses up to 'rp'. */
     if (RING_RESPONSE_PROD_OVERFLOW(&rinfo->ring, rp)) {
         pr_alert("%s: illegal number of responses %u\n",
              info->gd->disk_name, rp - rinfo->ring.rsp_cons);
         goto err;
     }
 
     for (i = rinfo->ring.rsp_cons; i != rp; i++) {
         unsigned long id;
         unsigned int op;
 
         eoiflag = 0;
 
         RING_COPY_RESPONSE(&rinfo->ring, i, &bret);
         id = bret.id;
 
         /*
          * The backend has messed up and given us an id that we would
          * never have given to it (we stamp it up to BLK_RING_SIZE -
          * look in get_id_from_freelist.
          */
         if (id >= BLK_RING_SIZE(info)) {
             pr_alert("%s: response has incorrect id (%ld)\n",
                  info->gd->disk_name, id);
             goto err;
         }
         if (rinfo->shadow[id].status != REQ_WAITING) {
             pr_alert("%s: response references no pending request\n",
                  info->gd->disk_name);
             goto err;
         }
 
         rinfo->shadow[id].status = REQ_PROCESSING;
         req  = rinfo->shadow[id].request;
 
         op = rinfo->shadow[id].req.operation;
         if (op == BLKIF_OP_INDIRECT)
             op = rinfo->shadow[id].req.u.indirect.indirect_op;
         if (bret.operation != op) {
             pr_alert("%s: response has wrong operation (%u instead of %u)\n",
                  info->gd->disk_name, bret.operation, op);
             goto err;
         }
 
         if (bret.operation != BLKIF_OP_DISCARD) {
             int ret;
 
             /*
              * We may need to wait for an extra response if the
              * I/O request is split in 2
              */
             ret = blkif_completion(&id, rinfo, &bret);
             if (!ret)
                 continue;
             if (unlikely(ret < 0))
                 goto err;
         }
 
         if (add_id_to_freelist(rinfo, id)) {
             WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
                  info->gd->disk_name, op_name(bret.operation), id);
             continue;
         }
 
         if (bret.status == BLKIF_RSP_OKAY)
             blkif_req(req)->error = BLK_STS_OK;
         else
             blkif_req(req)->error = BLK_STS_IOERR;
 
         switch (bret.operation) {
         case BLKIF_OP_DISCARD:
             if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
                 struct request_queue *rq = info->rq;
 
                 pr_warn_ratelimited("blkfront: %s: %s op failed\n",
                        info->gd->disk_name, op_name(bret.operation));
                 blkif_req(req)->error = BLK_STS_NOTSUPP;
                 info->feature_discard = 0;
                 info->feature_secdiscard = 0;
                 blk_queue_max_discard_sectors(rq, 0);
                 blk_queue_max_secure_erase_sectors(rq, 0);
             }
             break;
         case BLKIF_OP_FLUSH_DISKCACHE:
         case BLKIF_OP_WRITE_BARRIER:
             if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
                 pr_warn_ratelimited("blkfront: %s: %s op failed\n",
                        info->gd->disk_name, op_name(bret.operation));
                 blkif_req(req)->error = BLK_STS_NOTSUPP;
             }
             if (unlikely(bret.status == BLKIF_RSP_ERROR &&
                      rinfo->shadow[id].req.u.rw.nr_segments == 0)) {
                 pr_warn_ratelimited("blkfront: %s: empty %s op failed\n",
                        info->gd->disk_name, op_name(bret.operation));
                 blkif_req(req)->error = BLK_STS_NOTSUPP;
             }
             if (unlikely(blkif_req(req)->error)) {
                 if (blkif_req(req)->error == BLK_STS_NOTSUPP)
                     blkif_req(req)->error = BLK_STS_OK;
                 info->feature_fua = 0;
                 info->feature_flush = 0;
                 xlvbd_flush(info);
             }
             fallthrough;
         case BLKIF_OP_READ:
         case BLKIF_OP_WRITE:
             if (unlikely(bret.status != BLKIF_RSP_OKAY))
                 dev_dbg_ratelimited(&info->xbdev->dev,
                     "Bad return from blkdev data request: %#x\n",
                     bret.status);
 
             break;
         default:
             BUG();
         }
 
         if (likely(!blk_should_fake_timeout(req->q)))
             blk_mq_complete_request(req);
     }
 
     rinfo->ring.rsp_cons = i;
 
     if (i != rinfo->ring.req_prod_pvt) {
         int more_to_do;
         RING_FINAL_CHECK_FOR_RESPONSES(&rinfo->ring, more_to_do);
         if (more_to_do)
             goto again;
     } else
         rinfo->ring.sring->rsp_event = i + 1;
 
     kick_pending_request_queues_locked(rinfo);
 
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
 
     xen_irq_lateeoi(irq, eoiflag);
 
     return IRQ_HANDLED;
 
  err:
     info->connected = BLKIF_STATE_ERROR;
 
     spin_unlock_irqrestore(&rinfo->ring_lock, flags);
 
     /* No EOI in order to avoid further interrupts. */
 
     pr_alert("%s disabled for further use\n", info->gd->disk_name);
     return IRQ_HANDLED;
 }
 
 
 static int setup_blkring(struct xenbus_device *dev,
              struct blkfront_ring_info *rinfo)
 {
     struct blkif_sring *sring;
     int err;
     struct blkfront_info *info = rinfo->dev_info;
     unsigned long ring_size = info->nr_ring_pages * XEN_PAGE_SIZE;
 
     err = xenbus_setup_ring(dev, GFP_NOIO, (void **)&sring,
                 info->nr_ring_pages, rinfo->ring_ref);
     if (err)
         goto fail;
 
     XEN_FRONT_RING_INIT(&rinfo->ring, sring, ring_size);
 
     err = xenbus_alloc_evtchn(dev, &rinfo->evtchn);
     if (err)
         goto fail;
 
     err = bind_evtchn_to_irqhandler_lateeoi(rinfo->evtchn, blkif_interrupt,
                         0, "blkif", rinfo);
     if (err <= 0) {
         xenbus_dev_fatal(dev, err,
                  "bind_evtchn_to_irqhandler failed");
         goto fail;
     }
     rinfo->irq = err;
 
     return 0;
 fail:
     blkif_free(info, 0);
     return err;
 }
 
 /*
  * Write out per-ring/queue nodes including ring-ref and event-channel, and each
  * ring buffer may have multi pages depending on ->nr_ring_pages.
  */
 static int write_per_ring_nodes(struct xenbus_transaction xbt,
                 struct blkfront_ring_info *rinfo, const char *dir)
 {
     int err;
     unsigned int i;
     const char *message = NULL;
     struct blkfront_info *info = rinfo->dev_info;
 
     if (info->nr_ring_pages == 1) {
         err = xenbus_printf(xbt, dir, "ring-ref", "%u", rinfo->ring_ref[0]);
         if (err) {
             message = "writing ring-ref";
             goto abort_transaction;
         }
     } else {
         for (i = 0; i < info->nr_ring_pages; i++) {
             char ring_ref_name[RINGREF_NAME_LEN];
 
             snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
             err = xenbus_printf(xbt, dir, ring_ref_name,
                         "%u", rinfo->ring_ref[i]);
             if (err) {
                 message = "writing ring-ref";
                 goto abort_transaction;
             }
         }
     }
 
     err = xenbus_printf(xbt, dir, "event-channel", "%u", rinfo->evtchn);
     if (err) {
         message = "writing event-channel";
         goto abort_transaction;
     }
 
     return 0;
 
 abort_transaction:
     xenbus_transaction_end(xbt, 1);
     if (message)
         xenbus_dev_fatal(info->xbdev, err, "%s", message);
 
     return err;
 }
 
 /* Enable the persistent grants feature. */
 static bool feature_persistent = true;
 module_param(feature_persistent, bool, 0644);
 MODULE_PARM_DESC(feature_persistent,
         "Enables the persistent grants feature");
 
 /* Common code used when first setting up, and when resuming. */
 static int talk_to_blkback(struct xenbus_device *dev,
                struct blkfront_info *info)
 {
     const char *message = NULL;
     struct xenbus_transaction xbt;
     int err;
     unsigned int i, max_page_order;
     unsigned int ring_page_order;
     struct blkfront_ring_info *rinfo;
 
     if (!info)
         return -ENODEV;
 
     /* Check if backend is trusted. */
     info->bounce = !xen_blkif_trusted ||
                !xenbus_read_unsigned(dev->nodename, "trusted", 1);
 
     max_page_order = xenbus_read_unsigned(info->xbdev->otherend,
                           "max-ring-page-order", 0);
     ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
     info->nr_ring_pages = 1 << ring_page_order;
 
     err = negotiate_mq(info);
     if (err)
         goto destroy_blkring;
 
     for_each_rinfo(info, rinfo, i) {
         /* Create shared ring, alloc event channel. */
         err = setup_blkring(dev, rinfo);
         if (err)
             goto destroy_blkring;
     }
 
 again:
     err = xenbus_transaction_start(&xbt);
     if (err) {
         xenbus_dev_fatal(dev, err, "starting transaction");
         goto destroy_blkring;
     }
 
     if (info->nr_ring_pages > 1) {
         err = xenbus_printf(xbt, dev->nodename, "ring-page-order", "%u",
                     ring_page_order);
         if (err) {
             message = "writing ring-page-order";
             goto abort_transaction;
         }
     }
 
     /* We already got the number of queues/rings in _probe */
     if (info->nr_rings == 1) {
         err = write_per_ring_nodes(xbt, info->rinfo, dev->nodename);
         if (err)
             goto destroy_blkring;
     } else {
         char *path;
         size_t pathsize;
 
         err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u",
                     info->nr_rings);
         if (err) {
             message = "writing multi-queue-num-queues";
             goto abort_transaction;
         }
 
         pathsize = strlen(dev->nodename) + QUEUE_NAME_LEN;
         path = kmalloc(pathsize, GFP_KERNEL);
         if (!path) {
             err = -ENOMEM;
             message = "ENOMEM while writing ring references";
             goto abort_transaction;
         }
 
         for_each_rinfo(info, rinfo, i) {
             memset(path, 0, pathsize);
             snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
             err = write_per_ring_nodes(xbt, rinfo, path);
             if (err) {
                 kfree(path);
                 goto destroy_blkring;
             }
         }
         kfree(path);
     }
     err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
                 XEN_IO_PROTO_ABI_NATIVE);
     if (err) {
         message = "writing protocol";
         goto abort_transaction;
     }
     info->feature_persistent_parm = feature_persistent;
     err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
             info->feature_persistent_parm);
     if (err)
         dev_warn(&dev->dev,
              "writing persistent grants feature to xenbus");
 
     err = xenbus_transaction_end(xbt, 0);
     if (err) {
         if (err == -EAGAIN)
             goto again;
         xenbus_dev_fatal(dev, err, "completing transaction");
         goto destroy_blkring;
     }
 
     for_each_rinfo(info, rinfo, i) {
         unsigned int j;
 
         for (j = 0; j < BLK_RING_SIZE(info); j++)
             rinfo->shadow[j].req.u.rw.id = j + 1;
         rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
     }
     xenbus_switch_state(dev, XenbusStateInitialised);
 
     return 0;
 
  abort_transaction:
     xenbus_transaction_end(xbt, 1);
     if (message)
         xenbus_dev_fatal(dev, err, "%s", message);
  destroy_blkring:
     blkif_free(info, 0);
     return err;
 }
 
 static int negotiate_mq(struct blkfront_info *info)
 {
     unsigned int backend_max_queues;
     unsigned int i;
     struct blkfront_ring_info *rinfo;
 
     BUG_ON(info->nr_rings);
 
     /* Check if backend supports multiple queues. */
     backend_max_queues = xenbus_read_unsigned(info->xbdev->otherend,
                           "multi-queue-max-queues", 1);
     info->nr_rings = min(backend_max_queues, xen_blkif_max_queues);
     /* We need at least one ring. */
     if (!info->nr_rings)
         info->nr_rings = 1;
 
     info->rinfo_size = struct_size(info->rinfo, shadow,
                        BLK_RING_SIZE(info));
     info->rinfo = kvcalloc(info->nr_rings, info->rinfo_size, GFP_KERNEL);
     if (!info->rinfo) {
         xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
         info->nr_rings = 0;
         return -ENOMEM;
     }
 
     for_each_rinfo(info, rinfo, i) {
         INIT_LIST_HEAD(&rinfo->indirect_pages);
         INIT_LIST_HEAD(&rinfo->grants);
         rinfo->dev_info = info;
         INIT_WORK(&rinfo->work, blkif_restart_queue);
         spin_lock_init(&rinfo->ring_lock);
     }
     return 0;
 }
 
 /*
  * Entry point to this code when a new device is created.  Allocate the basic
  * structures and the ring buffer for communication with the backend, and
  * inform the backend of the appropriate details for those.  Switch to
  * Initialised state.
  */
 static int blkfront_probe(struct xenbus_device *dev,
               const struct xenbus_device_id *id)
 {
     int err, vdevice;
     struct blkfront_info *info;
 
     /* FIXME: Use dynamic device id if this is not set. */
     err = xenbus_scanf(XBT_NIL, dev->nodename,
                "virtual-device", "%i", &vdevice);
     if (err != 1) {
         /* go looking in the extended area instead */
         err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device-ext",
                    "%i", &vdevice);
         if (err != 1) {
             xenbus_dev_fatal(dev, err, "reading virtual-device");
             return err;
         }
     }
 
     if (xen_hvm_domain()) {
         char *type;
         int len;
         /* no unplug has been done: do not hook devices != xen vbds */
         if (xen_has_pv_and_legacy_disk_devices()) {
             int major;
 
             if (!VDEV_IS_EXTENDED(vdevice))
                 major = BLKIF_MAJOR(vdevice);
             else
                 major = XENVBD_MAJOR;
 
             if (major != XENVBD_MAJOR) {
                 printk(KERN_INFO
                         "%s: HVM does not support vbd %d as xen block device\n",
                         __func__, vdevice);
                 return -ENODEV;
             }
         }
         /* do not create a PV cdrom device if we are an HVM guest */
         type = xenbus_read(XBT_NIL, dev->nodename, "device-type", &len);
         if (IS_ERR(type))
             return -ENODEV;
         if (strncmp(type, "cdrom", 5) == 0) {
             kfree(type);
             return -ENODEV;
         }
         kfree(type);
     }
     info = kzalloc(sizeof(*info), GFP_KERNEL);
     if (!info) {
         xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");
         return -ENOMEM;
     }
 
     info->xbdev = dev;
 
     mutex_init(&info->mutex);
     info->vdevice = vdevice;
     info->connected = BLKIF_STATE_DISCONNECTED;
 
     /* Front end dir is a number, which is used as the id. */
     info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
     dev_set_drvdata(&dev->dev, info);
 
     mutex_lock(&blkfront_mutex);
     list_add(&info->info_list, &info_list);
     mutex_unlock(&blkfront_mutex);
 
     return 0;
 }
 
 static int blkif_recover(struct blkfront_info *info)
 {
     unsigned int r_index;
     struct request *req, *n;
     int rc;
     struct bio *bio;
     unsigned int segs;
     struct blkfront_ring_info *rinfo;
 
     blkfront_gather_backend_features(info);
     /* Reset limits changed by blk_mq_update_nr_hw_queues(). */
     blkif_set_queue_limits(info);
     segs = info->max_indirect_segments ? : BLKIF_MAX_SEGMENTS_PER_REQUEST;
     blk_queue_max_segments(info->rq, segs / GRANTS_PER_PSEG);
 
     for_each_rinfo(info, rinfo, r_index) {
         rc = blkfront_setup_indirect(rinfo);
         if (rc)
             return rc;
     }
     xenbus_switch_state(info->xbdev, XenbusStateConnected);
 
     /* Now safe for us to use the shared ring */
     info->connected = BLKIF_STATE_CONNECTED;
 
     for_each_rinfo(info, rinfo, r_index) {
         /* Kick any other new requests queued since we resumed */
         kick_pending_request_queues(rinfo);
     }
 
     list_for_each_entry_safe(req, n, &info->requests, queuelist) {
         /* Requeue pending requests (flush or discard) */
         list_del_init(&req->queuelist);
         BUG_ON(req->nr_phys_segments > segs);
         blk_mq_requeue_request(req, false);
     }
     blk_mq_start_stopped_hw_queues(info->rq, true);
     blk_mq_kick_requeue_list(info->rq);
 
     while ((bio = bio_list_pop(&info->bio_list)) != NULL) {
         /* Traverse the list of pending bios and re-queue them */
         submit_bio(bio);
     }
 
     return 0;
 }
 
 /*
  * We are reconnecting to the backend, due to a suspend/resume, or a backend
  * driver restart.  We tear down our blkif structure and recreate it, but
  * leave the device-layer structures intact so that this is transparent to the
  * rest of the kernel.
  */
 static int blkfront_resume(struct xenbus_device *dev)
 {
     struct blkfront_info *info = dev_get_drvdata(&dev->dev);
     int err = 0;
     unsigned int i, j;
     struct blkfront_ring_info *rinfo;
 
     dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);
 
     bio_list_init(&info->bio_list);
     INIT_LIST_HEAD(&info->requests);
     for_each_rinfo(info, rinfo, i) {
         struct bio_list merge_bio;
         struct blk_shadow *shadow = rinfo->shadow;
 
         for (j = 0; j < BLK_RING_SIZE(info); j++) {
             /* Not in use? */
             if (!shadow[j].request)
                 continue;
 
             /*
              * Get the bios in the request so we can re-queue them.
              */
             if (req_op(shadow[j].request) == REQ_OP_FLUSH ||
                 req_op(shadow[j].request) == REQ_OP_DISCARD ||
                 req_op(shadow[j].request) == REQ_OP_SECURE_ERASE ||
                 shadow[j].request->cmd_flags & REQ_FUA) {
                 /*
                  * Flush operations don't contain bios, so
                  * we need to requeue the whole request
                  *
                  * XXX: but this doesn't make any sense for a
                  * write with the FUA flag set..
                  */
                 list_add(&shadow[j].request->queuelist, &info->requests);
                 continue;
             }
             merge_bio.head = shadow[j].request->bio;
             merge_bio.tail = shadow[j].request->biotail;
             bio_list_merge(&info->bio_list, &merge_bio);
             shadow[j].request->bio = NULL;
             blk_mq_end_request(shadow[j].request, BLK_STS_OK);
         }
     }
 
     blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
 
     err = talk_to_blkback(dev, info);
     if (!err)
         blk_mq_update_nr_hw_queues(&info->tag_set, info->nr_rings);
 
     /*
      * We have to wait for the backend to switch to
      * connected state, since we want to read which
      * features it supports.
      */
 
     return err;
 }
 
 static void blkfront_closing(struct blkfront_info *info)
 {
     struct xenbus_device *xbdev = info->xbdev;
     struct blkfront_ring_info *rinfo;
     unsigned int i;
 
     if (xbdev->state == XenbusStateClosing)
         return;
 
     /* No more blkif_request(). */
     if (info->rq && info->gd) {
         blk_mq_stop_hw_queues(info->rq);
         blk_mark_disk_dead(info->gd);
         set_capacity(info->gd, 0);
     }
 
     for_each_rinfo(info, rinfo, i) {
         /* No more gnttab callback work. */
         gnttab_cancel_free_callback(&rinfo->callback);
 
         /* Flush gnttab callback work. Must be done with no locks held. */
         flush_work(&rinfo->work);
     }
 
     xenbus_frontend_closed(xbdev);
 }
 
 static void blkfront_setup_discard(struct blkfront_info *info)
 {
     info->feature_discard = 1;
     info->discard_granularity = xenbus_read_unsigned(info->xbdev->otherend,
                              "discard-granularity",
                              0);
     info->discard_alignment = xenbus_read_unsigned(info->xbdev->otherend,
                                "discard-alignment", 0);
     info->feature_secdiscard =
         !!xenbus_read_unsigned(info->xbdev->otherend, "discard-secure",
                        0);
 }
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo)
 {
     unsigned int psegs, grants, memflags;
     int err, i;
     struct blkfront_info *info = rinfo->dev_info;
 
     memflags = memalloc_noio_save();
 
     if (info->max_indirect_segments == 0) {
         if (!HAS_EXTRA_REQ)
             grants = BLKIF_MAX_SEGMENTS_PER_REQUEST;
         else {
             /*
              * When an extra req is required, the maximum
              * grants supported is related to the size of the
              * Linux block segment.
              */
             grants = GRANTS_PER_PSEG;
         }
     }
     else
         grants = info->max_indirect_segments;
     psegs = DIV_ROUND_UP(grants, GRANTS_PER_PSEG);
 
     err = fill_grant_buffer(rinfo,
                 (grants + INDIRECT_GREFS(grants)) * BLK_RING_SIZE(info));
     if (err)
         goto out_of_memory;
 
     if (!info->bounce && info->max_indirect_segments) {
         /*
          * We are using indirect descriptors but don't have a bounce
          * buffer, we need to allocate a set of pages that can be
          * used for mapping indirect grefs
          */
         int num = INDIRECT_GREFS(grants) * BLK_RING_SIZE(info);
 
         BUG_ON(!list_empty(&rinfo->indirect_pages));
         for (i = 0; i < num; i++) {
             struct page *indirect_page = alloc_page(GFP_KERNEL |
                                 __GFP_ZERO);
             if (!indirect_page)
                 goto out_of_memory;
             list_add(&indirect_page->lru, &rinfo->indirect_pages);
         }
     }
 
     for (i = 0; i < BLK_RING_SIZE(info); i++) {
         rinfo->shadow[i].grants_used =
             kvcalloc(grants,
                  sizeof(rinfo->shadow[i].grants_used[0]),
                  GFP_KERNEL);
         rinfo->shadow[i].sg = kvcalloc(psegs,
                            sizeof(rinfo->shadow[i].sg[0]),
                            GFP_KERNEL);
         if (info->max_indirect_segments)
             rinfo->shadow[i].indirect_grants =
                 kvcalloc(INDIRECT_GREFS(grants),
                      sizeof(rinfo->shadow[i].indirect_grants[0]),
                      GFP_KERNEL);
         if ((rinfo->shadow[i].grants_used == NULL) ||
             (rinfo->shadow[i].sg == NULL) ||
              (info->max_indirect_segments &&
              (rinfo->shadow[i].indirect_grants == NULL)))
             goto out_of_memory;
         sg_init_table(rinfo->shadow[i].sg, psegs);
     }
 
     memalloc_noio_restore(memflags);
 
     return 0;
 
 out_of_memory:
     for (i = 0; i < BLK_RING_SIZE(info); i++) {
         kvfree(rinfo->shadow[i].grants_used);
         rinfo->shadow[i].grants_used = NULL;
         kvfree(rinfo->shadow[i].sg);
         rinfo->shadow[i].sg = NULL;
         kvfree(rinfo->shadow[i].indirect_grants);
         rinfo->shadow[i].indirect_grants = NULL;
     }
     if (!list_empty(&rinfo->indirect_pages)) {
         struct page *indirect_page, *n;
         list_for_each_entry_safe(indirect_page, n, &rinfo->indirect_pages, lru) {
             list_del(&indirect_page->lru);
             __free_page(indirect_page);
         }
     }
 
     memalloc_noio_restore(memflags);
 
     return -ENOMEM;
 }
 
 /*
  * Gather all backend feature-*
  */
 static void blkfront_gather_backend_features(struct blkfront_info *info)
 {
     unsigned int indirect_segments;
 
     info->feature_flush = 0;
     info->feature_fua = 0;
 
     /*
      * If there's no "feature-barrier" defined, then it means
      * we're dealing with a very old backend which writes
      * synchronously; nothing to do.
      *
      * If there are barriers, then we use flush.
      */
     if (xenbus_read_unsigned(info->xbdev->otherend, "feature-barrier", 0)) {
         info->feature_flush = 1;
         info->feature_fua = 1;
     }
 
     /*
      * And if there is "feature-flush-cache" use that above
      * barriers.
      */
     if (xenbus_read_unsigned(info->xbdev->otherend, "feature-flush-cache",
                  0)) {
         info->feature_flush = 1;
         info->feature_fua = 0;
     }
 
     if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
         blkfront_setup_discard(info);
 
     if (info->feature_persistent_parm)
         info->feature_persistent =
             !!xenbus_read_unsigned(info->xbdev->otherend,
                            "feature-persistent", 0);
     if (info->feature_persistent)
         info->bounce = true;
 
     indirect_segments = xenbus_read_unsigned(info->xbdev->otherend,
                     "feature-max-indirect-segments", 0);
     if (indirect_segments > xen_blkif_max_segments)
         indirect_segments = xen_blkif_max_segments;
     if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST)
         indirect_segments = 0;
     info->max_indirect_segments = indirect_segments;
 
     if (info->feature_persistent) {
         mutex_lock(&blkfront_mutex);
         schedule_delayed_work(&blkfront_work, HZ * 10);
         mutex_unlock(&blkfront_mutex);
     }
 }
 
 /*
  * Invoked when the backend is finally 'ready' (and has told produced
  * the details about the physical device - #sectors, size, etc).
  */
 static void blkfront_connect(struct blkfront_info *info)
 {
     unsigned long long sectors;
     unsigned long sector_size;
     unsigned int physical_sector_size;
     int err, i;
     struct blkfront_ring_info *rinfo;
 
     switch (info->connected) {
     case BLKIF_STATE_CONNECTED:
         /*
          * Potentially, the back-end may be signalling
          * a capacity change; update the capacity.
          */
         err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                    "sectors", "%Lu", &sectors);
         if (XENBUS_EXIST_ERR(err))
             return;
         printk(KERN_INFO "Setting capacity to %Lu\n",
                sectors);
         set_capacity_and_notify(info->gd, sectors);
 
         return;
     case BLKIF_STATE_SUSPENDED:
         /*
          * If we are recovering from suspension, we need to wait
          * for the backend to announce it's features before
          * reconnecting, at least we need to know if the backend
          * supports indirect descriptors, and how many.
          */
         blkif_recover(info);
         return;
 
     default:
         break;
     }
 
     dev_dbg(&info->xbdev->dev, "%s:%s.\n",
         __func__, info->xbdev->otherend);
 
     err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                 "sectors", "%llu", &sectors,
                 "info", "%u", &info->vdisk_info,
                 "sector-size", "%lu", &sector_size,
                 NULL);
     if (err) {
         xenbus_dev_fatal(info->xbdev, err,
                  "reading backend fields at %s",
                  info->xbdev->otherend);
         return;
     }
 
     /*
      * physical-sector-size is a newer field, so old backends may not
      * provide this. Assume physical sector size to be the same as
      * sector_size in that case.
      */
     physical_sector_size = xenbus_read_unsigned(info->xbdev->otherend,
                             "physical-sector-size",
                             sector_size);
     blkfront_gather_backend_features(info);
     for_each_rinfo(info, rinfo, i) {
         err = blkfront_setup_indirect(rinfo);
         if (err) {
             xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
                      info->xbdev->otherend);
             blkif_free(info, 0);
             break;
         }
     }
 
     err = xlvbd_alloc_gendisk(sectors, info, sector_size,
                   physical_sector_size);
     if (err) {
         xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
                  info->xbdev->otherend);
         goto fail;
     }
 
     xenbus_switch_state(info->xbdev, XenbusStateConnected);
 
     /* Kick pending requests. */
     info->connected = BLKIF_STATE_CONNECTED;
     for_each_rinfo(info, rinfo, i)
         kick_pending_request_queues(rinfo);
 
     err = device_add_disk(&info->xbdev->dev, info->gd, NULL);
     if (err) {
         put_disk(info->gd);
         blk_mq_free_tag_set(&info->tag_set);
         info->rq = NULL;
         goto fail;
     }
 
     info->is_ready = 1;
     return;
 
 fail:
     blkif_free(info, 0);
     return;
 }
 
 /*
  * Callback received when the backend's state changes.
  */
 static void blkback_changed(struct xenbus_device *dev,
                 enum xenbus_state backend_state)
 {
     struct blkfront_info *info = dev_get_drvdata(&dev->dev);
 
     dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);
 
     switch (backend_state) {
     case XenbusStateInitWait:
         if (dev->state != XenbusStateInitialising)
             break;
         if (talk_to_blkback(dev, info))
             break;
         break;
     case XenbusStateInitialising:
     case XenbusStateInitialised:
     case XenbusStateReconfiguring:
     case XenbusStateReconfigured:
     case XenbusStateUnknown:
         break;
 
     case XenbusStateConnected:
         /*
          * talk_to_blkback sets state to XenbusStateInitialised
          * and blkfront_connect sets it to XenbusStateConnected
          * (if connection went OK).
          *
          * If the backend (or toolstack) decides to poke at backend
          * state (and re-trigger the watch by setting the state repeatedly
          * to XenbusStateConnected (4)) we need to deal with this.
          * This is allowed as this is used to communicate to the guest
          * that the size of disk has changed!
          */
         if ((dev->state != XenbusStateInitialised) &&
             (dev->state != XenbusStateConnected)) {
             if (talk_to_blkback(dev, info))
                 break;
         }
 
         blkfront_connect(info);
         break;
 
     case XenbusStateClosed:
         if (dev->state == XenbusStateClosed)
             break;
         fallthrough;
     case XenbusStateClosing:
         blkfront_closing(info);
         break;
     }
 }
 
 static int blkfront_remove(struct xenbus_device *xbdev)
 {
     struct blkfront_info *info = dev_get_drvdata(&xbdev->dev);
 
     dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);
 
     if (info->gd)
         del_gendisk(info->gd);
 
     mutex_lock(&blkfront_mutex);
     list_del(&info->info_list);
     mutex_unlock(&blkfront_mutex);
 
     blkif_free(info, 0);
     if (info->gd) {
         xlbd_release_minors(info->gd->first_minor, info->gd->minors);
         put_disk(info->gd);
         blk_mq_free_tag_set(&info->tag_set);
     }
 
     kfree(info);
     return 0;
 }
 
 static int blkfront_is_ready(struct xenbus_device *dev)
 {
     struct blkfront_info *info = dev_get_drvdata(&dev->dev);
 
     return info->is_ready && info->xbdev;
 }
 
 static const struct block_device_operations xlvbd_block_fops =
 {
     .owner = THIS_MODULE,
     .getgeo = blkif_getgeo,
     .ioctl = blkif_ioctl,
     .compat_ioctl = blkdev_compat_ptr_ioctl,
 };
 
 
 static const struct xenbus_device_id blkfront_ids[] = {
     { "vbd" },
     { "" }
 };
 
 static struct xenbus_driver blkfront_driver = {
     .ids  = blkfront_ids,
     .probe = blkfront_probe,
     .remove = blkfront_remove,
     .resume = blkfront_resume,
     .otherend_changed = blkback_changed,
     .is_ready = blkfront_is_ready,
 };
 
 static void purge_persistent_grants(struct blkfront_info *info)
 {
     unsigned int i;
     unsigned long flags;
     struct blkfront_ring_info *rinfo;
 
     for_each_rinfo(info, rinfo, i) {
         struct grant *gnt_list_entry, *tmp;
         LIST_HEAD(grants);
 
         spin_lock_irqsave(&rinfo->ring_lock, flags);
 
         if (rinfo->persistent_gnts_c == 0) {
             spin_unlock_irqrestore(&rinfo->ring_lock, flags);
             continue;
         }
 
         list_for_each_entry_safe(gnt_list_entry, tmp, &rinfo->grants,
                      node) {
             if (gnt_list_entry->gref == INVALID_GRANT_REF ||
                 !gnttab_try_end_foreign_access(gnt_list_entry->gref))
                 continue;
 
             list_del(&gnt_list_entry->node);
             rinfo->persistent_gnts_c--;
             gnt_list_entry->gref = INVALID_GRANT_REF;
             list_add_tail(&gnt_list_entry->node, &grants);
         }
 
         list_splice_tail(&grants, &rinfo->grants);
 
         spin_unlock_irqrestore(&rinfo->ring_lock, flags);
     }
 }
 
 static void blkfront_delay_work(struct work_struct *work)
 {
     struct blkfront_info *info;
     bool need_schedule_work = false;
 
     /*
      * Note that when using bounce buffers but not persistent grants
      * there's no need to run blkfront_delay_work because grants are
      * revoked in blkif_completion or else an error is reported and the
      * connection is closed.
      */
 
     mutex_lock(&blkfront_mutex);
 
     list_for_each_entry(info, &info_list, info_list) {
         if (info->feature_persistent) {
             need_schedule_work = true;
             mutex_lock(&info->mutex);
             purge_persistent_grants(info);
             mutex_unlock(&info->mutex);
         }
     }
 
     if (need_schedule_work)
         schedule_delayed_work(&blkfront_work, HZ * 10);
 
     mutex_unlock(&blkfront_mutex);
 }
 
 static int __init xlblk_init(void)
 {
     int ret;
     int nr_cpus = num_online_cpus();
 
     if (!xen_domain())
         return -ENODEV;
 
     if (!xen_has_pv_disk_devices())
         return -ENODEV;
 
     if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
         pr_warn("xen_blk: can't get major %d with name %s\n",
             XENVBD_MAJOR, DEV_NAME);
         return -ENODEV;
     }
 
     if (xen_blkif_max_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST)
         xen_blkif_max_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
 
     if (xen_blkif_max_ring_order > XENBUS_MAX_RING_GRANT_ORDER) {
         pr_info("Invalid max_ring_order (%d), will use default max: %d.\n",
             xen_blkif_max_ring_order, XENBUS_MAX_RING_GRANT_ORDER);
         xen_blkif_max_ring_order = XENBUS_MAX_RING_GRANT_ORDER;
     }
 
     if (xen_blkif_max_queues > nr_cpus) {
         pr_info("Invalid max_queues (%d), will use default max: %d.\n",
             xen_blkif_max_queues, nr_cpus);
         xen_blkif_max_queues = nr_cpus;
     }
 
     INIT_DELAYED_WORK(&blkfront_work, blkfront_delay_work);
 
     ret = xenbus_register_frontend(&blkfront_driver);
     if (ret) {
         unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
         return ret;
     }
 
     return 0;
 }
 module_init(xlblk_init);
 
 
 static void __exit xlblk_exit(void)
 {
     cancel_delayed_work_sync(&blkfront_work);
 
     xenbus_unregister_driver(&blkfront_driver);
     unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
     kfree(minors);
 }
 module_exit(xlblk_exit);
 
 MODULE_DESCRIPTION("Xen virtual block device frontend");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_BLOCKDEV_MAJOR(XENVBD_MAJOR);
 MODULE_ALIAS("xen:vbd");
 MODULE_ALIAS("xenblk");