Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[cris-mirror.git] / drivers / block / xen-blkfront.c

/*
 * 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/mutex.h>
#include <linux/scatterlist.h>
#include <linux/bitmap.h>
#include <linux/list.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,
};

struct grant {
        grant_ref_t gref;
        struct page *page;
        struct list_head node;
};

enum blk_req_status {
        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 split_bio {
        struct bio *bio;
        atomic_t pending;
};

static DEFINE_MUTEX(blkfront_mutex);
static const struct block_device_operations xlvbd_block_fops;

/*
 * 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,
                   S_IRUGO);
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, S_IRUGO);
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, S_IRUGO);
MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");

#define BLK_RING_SIZE(info)     \
        __CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * (info)->nr_ring_pages)

#define BLK_MAX_RING_SIZE       \
        __CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * XENBUS_MAX_RING_GRANTS)

/*
 * 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 blk_shadow shadow[BLK_MAX_RING_SIZE];
        struct list_head indirect_pages;
        struct list_head grants;
        unsigned int persistent_gnts_c;
        unsigned long shadow_free;
        struct blkfront_info *dev_info;
};

/*
 * 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;
        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;
        unsigned int feature_fua;
        unsigned int feature_discard:1;
        unsigned int feature_secdiscard:1;
        unsigned int discard_granularity;
        unsigned int discard_alignment;
        unsigned int feature_persistent:1;
        /* 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;
        /* Save uncomplete reqs and bios for migration. */
        struct list_head requests;
        struct bio_list bio_list;
};

static unsigned int nr_minors;
static unsigned long *minors;
static DEFINE_SPINLOCK(minor_lock);

#define GRANT_INVALID_REF       0

#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 PSEGS_PER_INDIRECT_FRAME        \
        (GRANTS_INDIRECT_FRAME / GRANTS_PSEGS)

#define INDIRECT_GREFS(_grants)         \
        DIV_ROUND_UP(_grants, GRANTS_PER_INDIRECT_FRAME)

#define GREFS(_psegs)   ((_psegs) * GRANTS_PER_PSEG)

static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo);
static void blkfront_gather_backend_features(struct blkfront_info *info);

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->feature_persistent) {
                        granted_page = alloc_page(GFP_NOIO);
                        if (!granted_page) {
                                kfree(gnt_list_entry);
                                goto out_of_memory;
                        }
                        gnt_list_entry->page = granted_page;
                }

                gnt_list_entry->gref = GRANT_INVALID_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->feature_persistent)
                        __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 != GRANT_INVALID_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 != GRANT_INVALID_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->feature_persistent)
                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 != GRANT_INVALID_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->feature_persistent) {
                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;

        dev_dbg(&info->xbdev->dev, "command: 0x%x, argument: 0x%lx\n",
                command, (long)argument);

        switch (command) {
        case CDROMMULTISESSION:
                dev_dbg(&info->xbdev->dev, "FIXME: support multisession CDs later\n");
                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: {
                struct gendisk *gd = info->gd;
                if (gd->flags & GENHD_FL_CD)
                        return 0;
                return -EINVAL;
        }

        default:
                /*printk(KERN_ALERT "ioctl %08x not supported by Xen blkdev\n",
                  command);*/
                return -EINVAL; /* same return as native Linux */
        }

        return 0;
}

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_WAITING;
        rinfo->shadow[id].associated_id = NO_ASSOCIATED_ID;

        (*ring_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;
        unsigned long id;

        /* Fill out a communications ring structure. */
        id = blkif_ring_get_request(rinfo, req, &ring_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;

        /* Keep a private copy so we can reissue requests when recovering. */
        rinfo->shadow[id].req = *ring_req;

        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 read 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;
        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->feature_persistent,
        };

        /*
         * 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.
         */
        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);

        /*
         * We have to reserve 'max_grefs' grants because persistent
         * grants are shared by all rings.
         */
        if (max_grefs > 0)
                if (gnttab_alloc_grant_references(max_grefs, &setup.gref_head) < 0) {
                        gnttab_request_free_callback(
                                &rinfo->callback,
                                blkif_restart_queue_callback,
                                rinfo,
                                max_grefs);
                        return 1;
                }

        /* Fill out a communications ring structure. */
        id = blkif_ring_get_request(rinfo, req, &ring_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,
                                                          &extra_ring_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);

        /* Keep a private copy so we can reissue requests when recovering. */
        rinfo->shadow[id].req = *ring_req;
        if (unlikely(require_extra_req))
                rinfo->shadow[extra_id].req = *extra_ring_req;

        if (max_grefs > 0)
                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 ((req->cmd_type != REQ_TYPE_FS) ||
                ((req_op(req) == REQ_OP_FLUSH) &&
                 !info->feature_flush) ||
                ((req->cmd_flags & REQ_FUA) &&
                 !info->feature_fua));
}

static int 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;

        BUG_ON(info->nr_rings <= qid);
        rinfo = &info->rinfo[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_MQ_RQ_QUEUE_OK;

out_err:
        spin_unlock_irqrestore(&rinfo->ring_lock, flags);
        return BLK_MQ_RQ_QUEUE_ERROR;

out_busy:
        spin_unlock_irqrestore(&rinfo->ring_lock, flags);
        blk_mq_stop_hw_queue(hctx);
        return BLK_MQ_RQ_QUEUE_BUSY;
}

static struct blk_mq_ops blkfront_mq_ops = {
        .queue_rq = blkif_queue_rq,
        .map_queue = blk_mq_map_queue,
};

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;

        queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);

        if (info->feature_discard) {
                queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, rq);
                blk_queue_max_discard_sectors(rq, get_capacity(gd));
                rq->limits.discard_granularity = info->discard_granularity;
                rq->limits.discard_alignment = info->discard_alignment;
                if (info->feature_secdiscard)
                        queue_flag_set_unlocked(QUEUE_FLAG_SECERASE, rq);
        }

        /* 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);

        /* Make sure we don't use bounce buffers. */
        blk_queue_bounce_limit(rq, BLK_BOUNCE_ANY);
}

static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
                                unsigned int physical_sector_size)
{
        struct request_queue *rq;
        struct blkfront_info *info = gd->private_data;

        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 | BLK_MQ_F_SG_MERGE;
        info->tag_set.cmd_size = 0;
        info->tag_set.driver_data = info;

        if (blk_mq_alloc_tag_set(&info->tag_set))
                return -EINVAL;
        rq = blk_mq_init_queue(&info->tag_set);
        if (IS_ERR(rq)) {
                blk_mq_free_tag_set(&info->tag_set);
                return PTR_ERR(rq);
        }

        rq->queuedata = info;
        info->rq = gd->queue = rq;
        info->gd = gd;
        info->sector_size = sector_size;
        info->physical_sector_size = physical_sector_size;
        blkif_set_queue_limits(info);

        return 0;
}

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\n",
                info->gd->disk_name, flush_info(info),
                "persistent grants:", info->feature_persistent ?
                "enabled;" : "disabled;", "indirect descriptors:",
                info->max_indirect_segments ? "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 vdisk_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)
                goto out;
        err = -ENODEV;

        gd = alloc_disk(nr_minors);
        if (gd == NULL)
                goto release;

        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->fops = &xlvbd_block_fops;
        gd->private_data = info;
        set_capacity(gd, capacity);

        if (xlvbd_init_blk_queue(gd, sector_size, physical_sector_size)) {
                del_gendisk(gd);
                goto release;
        }

        xlvbd_flush(info);

        if (vdisk_info & VDISK_READONLY)
                set_disk_ro(gd, 1);

        if (vdisk_info & VDISK_REMOVABLE)
                gd->flags |= GENHD_FL_REMOVABLE;

        if (vdisk_info & VDISK_CDROM)
                gd->flags |= GENHD_FL_CD;

        return 0;

 release:
        xlbd_release_minors(minor, nr_minors);
 out:
        return err;
}

static void xlvbd_release_gendisk(struct blkfront_info *info)
{
        unsigned int minor, nr_minors, i;

        if (info->rq == NULL)
                return;

        /* No more blkif_request(). */
        blk_mq_stop_hw_queues(info->rq);

        for (i = 0; i < info->nr_rings; i++) {
                struct blkfront_ring_info *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);
        }

        del_gendisk(info->gd);

        minor = info->gd->first_minor;
        nr_minors = info->gd->minors;
        xlbd_release_minors(minor, nr_minors);

        blk_cleanup_queue(info->rq);
        blk_mq_free_tag_set(&info->tag_set);
        info->rq = NULL;

        put_disk(info->gd);
        info->gd = NULL;
}

/* 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->feature_persistent);
                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 != GRANT_INVALID_REF) {
                                gnttab_end_foreign_access(persistent_gnt->gref,
                                                          0, 0UL);
                                rinfo->persistent_gnts_c--;
                        }
                        if (info->feature_persistent)
                                __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, 0, 0UL);
                        if (info->feature_persistent)
                                __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, 0, 0UL);
                        __free_page(persistent_gnt->page);
                        kfree(persistent_gnt);
                }

free_shadow:
                kfree(rinfo->shadow[i].grants_used);
                rinfo->shadow[i].grants_used = NULL;
                kfree(rinfo->shadow[i].indirect_grants);
                rinfo->shadow[i].indirect_grants = NULL;
                kfree(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. */
        for (i = 0; i < info->nr_ring_pages; i++) {
                if (rinfo->ring_ref[i] != GRANT_INVALID_REF) {
                        gnttab_end_foreign_access(rinfo->ring_ref[i], 0, 0);
                        rinfo->ring_ref[i] = GRANT_INVALID_REF;
                }
        }
        free_pages((unsigned long)rinfo->ring.sring, get_order(info->nr_ring_pages * XEN_PAGE_SIZE));
        rinfo->ring.sring = NULL;

        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;

        /* 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 (i = 0; i < info->nr_rings; i++)
                blkif_free_ring(&info->rinfo[i]);

        kfree(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:
                /* Fallthrough. */
        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_WAITING);
        BUG_ON(s2 == REQ_WAITING);

        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;
}

static bool 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_WAITING)
                        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->feature_persistent) {
                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_query_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_ratelimited("backed has not unmapped grant: %u\n",
                                                     s->grants_used[i]->gref);
                        list_add(&s->grants_used[i]->node, &rinfo->grants);
                        rinfo->persistent_gnts_c++;
                } else {
                        /*
                         * If the grant is not mapped by the backend we end the
                         * foreign access and add it to the tail of the list,
                         * so it will not be picked again unless we run out of
                         * persistent grants.
                         */
                        gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
                        s->grants_used[i]->gref = GRANT_INVALID_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_query_foreign_access(s->indirect_grants[i]->gref)) {
                                if (!info->feature_persistent)
                                        pr_alert_ratelimited("backed has not unmapped grant: %u\n",
                                                             s->indirect_grants[i]->gref);
                                list_add(&s->indirect_grants[i]->node, &rinfo->grants);
                                rinfo->persistent_gnts_c++;
                        } else {
                                struct page *indirect_page;

                                gnttab_end_foreign_access(s->indirect_grants[i]->gref, 0, 0UL);
                                /*
                                 * Add the used indirect page back to the list of
                                 * available pages for indirect grefs.
                                 */
                                if (!info->feature_persistent) {
                                        indirect_page = s->indirect_grants[i]->page;
                                        list_add(&indirect_page->lru, &rinfo->indirect_pages);
                                }
                                s->indirect_grants[i]->gref = GRANT_INVALID_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;
        int error;

        if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
                return IRQ_HANDLED;

        spin_lock_irqsave(&rinfo->ring_lock, flags);
 again:
        rp = rinfo->ring.sring->rsp_prod;
        rmb(); /* Ensure we see queued responses up to 'rp'. */

        for (i = rinfo->ring.rsp_cons; i != rp; i++) {
                unsigned long id;

                bret = RING_GET_RESPONSE(&rinfo->ring, i);
                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)) {
                        WARN(1, "%s: response to %s has incorrect id (%ld)\n",
                             info->gd->disk_name, op_name(bret->operation), id);
                        /* We can't safely get the 'struct request' as
                         * the id is busted. */
                        continue;
                }
                req  = rinfo->shadow[id].request;

                if (bret->operation != BLKIF_OP_DISCARD) {
                        /*
                         * We may need to wait for an extra response if the
                         * I/O request is split in 2
                         */
                        if (!blkif_completion(&id, rinfo, bret))
                                continue;
                }

                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;
                }

                error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
                switch (bret->operation) {
                case BLKIF_OP_DISCARD:
                        if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
                                struct request_queue *rq = info->rq;
                                printk(KERN_WARNING "blkfront: %s: %s op failed\n",
                                           info->gd->disk_name, op_name(bret->operation));
                                error = -EOPNOTSUPP;
                                info->feature_discard = 0;
                                info->feature_secdiscard = 0;
                                queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
                                queue_flag_clear(QUEUE_FLAG_SECERASE, rq);
                        }
                        blk_mq_complete_request(req, error);
                        break;
                case BLKIF_OP_FLUSH_DISKCACHE:
                case BLKIF_OP_WRITE_BARRIER:
                        if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
                                printk(KERN_WARNING "blkfront: %s: %s op failed\n",
                                       info->gd->disk_name, op_name(bret->operation));
                                error = -EOPNOTSUPP;
                        }
                        if (unlikely(bret->status == BLKIF_RSP_ERROR &&
                                     rinfo->shadow[id].req.u.rw.nr_segments == 0)) {
                                printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
                                       info->gd->disk_name, op_name(bret->operation));
                                error = -EOPNOTSUPP;
                        }
                        if (unlikely(error)) {
                                if (error == -EOPNOTSUPP)
                                        error = 0;
                                info->feature_fua = 0;
                                info->feature_flush = 0;
                                xlvbd_flush(info);
                        }
                        /* fall through */
                case BLKIF_OP_READ:
                case BLKIF_OP_WRITE:
                        if (unlikely(bret->status != BLKIF_RSP_OKAY))
                                dev_dbg(&info->xbdev->dev, "Bad return from blkdev data "
                                        "request: %x\n", bret->status);

                        blk_mq_complete_request(req, error);
                        break;
                default:
                        BUG();
                }
        }

        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);

        return IRQ_HANDLED;
}


static int setup_blkring(struct xenbus_device *dev,
                         struct blkfront_ring_info *rinfo)
{
        struct blkif_sring *sring;
        int err, i;
        struct blkfront_info *info = rinfo->dev_info;
        unsigned long ring_size = info->nr_ring_pages * XEN_PAGE_SIZE;
        grant_ref_t gref[XENBUS_MAX_RING_GRANTS];

        for (i = 0; i < info->nr_ring_pages; i++)
                rinfo->ring_ref[i] = GRANT_INVALID_REF;

        sring = (struct blkif_sring *)__get_free_pages(GFP_NOIO | __GFP_HIGH,
                                                       get_order(ring_size));
        if (!sring) {
                xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
                return -ENOMEM;
        }
        SHARED_RING_INIT(sring);
        FRONT_RING_INIT(&rinfo->ring, sring, ring_size);

        err = xenbus_grant_ring(dev, rinfo->ring.sring, info->nr_ring_pages, gref);
        if (err < 0) {
                free_pages((unsigned long)sring, get_order(ring_size));
                rinfo->ring.sring = NULL;
                goto fail;
        }
        for (i = 0; i < info->nr_ring_pages; i++)
                rinfo->ring_ref[i] = gref[i];

        err = xenbus_alloc_evtchn(dev, &rinfo->evtchn);
        if (err)
                goto fail;

        err = bind_evtchn_to_irqhandler(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;
}

/* 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 = 0;
        unsigned int ring_page_order = 0;

        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "max-ring-page-order", "%u", &max_page_order);
        if (err != 1)
                info->nr_ring_pages = 1;
        else {
                ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
                info->nr_ring_pages = 1 << ring_page_order;
        }

        for (i = 0; i < info->nr_rings; i++) {
                struct blkfront_ring_info *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[0], 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 (i = 0; i < info->nr_rings; i++) {
                        memset(path, 0, pathsize);
                        snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
                        err = write_per_ring_nodes(xbt, &info->rinfo[i], 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;
        }
        err = xenbus_printf(xbt, dev->nodename,
                            "feature-persistent", "%u", 1);
        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 (i = 0; i < info->nr_rings; i++) {
                unsigned int j;
                struct blkfront_ring_info *rinfo = &info->rinfo[i];

                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);

        kfree(info);
        dev_set_drvdata(&dev->dev, NULL);

        return err;
}

static int negotiate_mq(struct blkfront_info *info)
{
        unsigned int backend_max_queues = 0;
        int err;
        unsigned int i;

        BUG_ON(info->nr_rings);

        /* Check if backend supports multiple queues. */
        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "multi-queue-max-queues", "%u", &backend_max_queues);
        if (err < 0)
                backend_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 = kzalloc(sizeof(struct blkfront_ring_info) * info->nr_rings, GFP_KERNEL);
        if (!info->rinfo) {
                xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
                return -ENOMEM;
        }

        for (i = 0; i < info->nr_rings; i++) {
                struct blkfront_ring_info *rinfo;

                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;
        err = negotiate_mq(info);
        if (err) {
                kfree(info);
                return err;
        }

        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);

        return 0;
}

static void split_bio_end(struct bio *bio)
{
        struct split_bio *split_bio = bio->bi_private;

        if (atomic_dec_and_test(&split_bio->pending)) {
                split_bio->bio->bi_phys_segments = 0;
                split_bio->bio->bi_error = bio->bi_error;
                bio_endio(split_bio->bio);
                kfree(split_bio);
        }
        bio_put(bio);
}

static int blkif_recover(struct blkfront_info *info)
{
        unsigned int i, r_index;
        struct request *req, *n;
        int rc;
        struct bio *bio, *cloned_bio;
        unsigned int segs, offset;
        int pending, size;
        struct split_bio *split_bio;

        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 (r_index = 0; r_index < info->nr_rings; r_index++) {
                struct blkfront_ring_info *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 (r_index = 0; r_index < info->nr_rings; r_index++) {
                struct blkfront_ring_info *rinfo;

                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);
        }
        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 */
                if (bio_segments(bio) > segs) {
                        /*
                         * This bio has more segments than what we can
                         * handle, we have to split it.
                         */
                        pending = (bio_segments(bio) + segs - 1) / segs;
                        split_bio = kzalloc(sizeof(*split_bio), GFP_NOIO);
                        BUG_ON(split_bio == NULL);
                        atomic_set(&split_bio->pending, pending);
                        split_bio->bio = bio;
                        for (i = 0; i < pending; i++) {
                                offset = (i * segs * XEN_PAGE_SIZE) >> 9;
                                size = min((unsigned int)(segs * XEN_PAGE_SIZE) >> 9,
                                           (unsigned int)bio_sectors(bio) - offset);
                                cloned_bio = bio_clone(bio, GFP_NOIO);
                                BUG_ON(cloned_bio == NULL);
                                bio_trim(cloned_bio, offset, size);
                                cloned_bio->bi_private = split_bio;
                                cloned_bio->bi_end_io = split_bio_end;
                                submit_bio(cloned_bio);
                        }
                        /*
                         * Now we have to wait for all those smaller bios to
                         * end, so we can also end the "parent" bio.
                         */
                        continue;
                }
                /* We don't need to split this bio */
                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;

        dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);

        bio_list_init(&info->bio_list);
        INIT_LIST_HEAD(&info->requests);
        for (i = 0; i < info->nr_rings; i++) {
                struct blkfront_ring_info *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[i].request) == REQ_OP_FLUSH ||
                            req_op(shadow[i].request) == REQ_OP_DISCARD ||
                            req_op(shadow[i].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, 0);
                }
        }

        blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);

        err = negotiate_mq(info);
        if (err)
                return err;

        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 block_device *bdev = NULL;

        mutex_lock(&info->mutex);

        if (xbdev->state == XenbusStateClosing) {
                mutex_unlock(&info->mutex);
                return;
        }

        if (info->gd)
                bdev = bdget_disk(info->gd, 0);

        mutex_unlock(&info->mutex);

        if (!bdev) {
                xenbus_frontend_closed(xbdev);
                return;
        }

        mutex_lock(&bdev->bd_mutex);

        if (bdev->bd_openers) {
                xenbus_dev_error(xbdev, -EBUSY,
                                 "Device in use; refusing to close");
                xenbus_switch_state(xbdev, XenbusStateClosing);
        } else {
                xlvbd_release_gendisk(info);
                xenbus_frontend_closed(xbdev);
        }

        mutex_unlock(&bdev->bd_mutex);
        bdput(bdev);
}

static void blkfront_setup_discard(struct blkfront_info *info)
{
        int err;
        unsigned int discard_granularity;
        unsigned int discard_alignment;
        unsigned int discard_secure;

        info->feature_discard = 1;
        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                "discard-granularity", "%u", &discard_granularity,
                "discard-alignment", "%u", &discard_alignment,
                NULL);
        if (!err) {
                info->discard_granularity = discard_granularity;
                info->discard_alignment = discard_alignment;
        }
        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "discard-secure", "%u", &discard_secure);
        if (err > 0)
                info->feature_secdiscard = !!discard_secure;
}

static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo)
{
        unsigned int psegs, grants;
        int err, i;
        struct blkfront_info *info = rinfo->dev_info;

        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 = 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->feature_persistent && info->max_indirect_segments) {
                /*
                 * We are using indirect descriptors but not persistent
                 * grants, 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_NOIO);
                        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 = kzalloc(
                        sizeof(rinfo->shadow[i].grants_used[0]) * grants,
                        GFP_NOIO);
                rinfo->shadow[i].sg = kzalloc(sizeof(rinfo->shadow[i].sg[0]) * psegs, GFP_NOIO);
                if (info->max_indirect_segments)
                        rinfo->shadow[i].indirect_grants = kzalloc(
                                sizeof(rinfo->shadow[i].indirect_grants[0]) *
                                INDIRECT_GREFS(grants),
                                GFP_NOIO);
                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);
        }


        return 0;

out_of_memory:
        for (i = 0; i < BLK_RING_SIZE(info); i++) {
                kfree(rinfo->shadow[i].grants_used);
                rinfo->shadow[i].grants_used = NULL;
                kfree(rinfo->shadow[i].sg);
                rinfo->shadow[i].sg = NULL;
                kfree(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);
                }
        }
        return -ENOMEM;
}

/*
 * Gather all backend feature-*
 */
static void blkfront_gather_backend_features(struct blkfront_info *info)
{
        int err;
        int barrier, flush, discard, persistent;
        unsigned int indirect_segments;

        info->feature_flush = 0;
        info->feature_fua = 0;

        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-barrier", "%d", &barrier);

        /*
         * 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 (err > 0 && barrier) {
                info->feature_flush = 1;
                info->feature_fua = 1;
        }

        /*
         * And if there is "feature-flush-cache" use that above
         * barriers.
         */
        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-flush-cache", "%d", &flush);

        if (err > 0 && flush) {
                info->feature_flush = 1;
                info->feature_fua = 0;
        }

        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-discard", "%d", &discard);

        if (err > 0 && discard)
                blkfront_setup_discard(info);

        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-persistent", "%d", &persistent);
        if (err <= 0)
                info->feature_persistent = 0;
        else
                info->feature_persistent = persistent;

        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "feature-max-indirect-segments", "%u",
                           &indirect_segments);
        if (err <= 0)
                info->max_indirect_segments = 0;
        else
                info->max_indirect_segments = min(indirect_segments,
                                                  xen_blkif_max_segments);
}

/*
 * 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;
        unsigned int binfo;
        int err, i;

        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(info->gd, sectors);
                revalidate_disk(info->gd);

                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", &binfo,
                            "sector-size", "%lu", &sector_size,
                            NULL);
        if (err) {
                xenbus_dev_fatal(info->xbdev, err,
                                 "reading backend fields at %s",
                                 info->xbdev->otherend);
                return;
        }

        /*
         * physcial-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.
         */
        err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                           "physical-sector-size", "%u", &physical_sector_size);
        if (err != 1)
                physical_sector_size = sector_size;

        blkfront_gather_backend_features(info);
        for (i = 0; i < info->nr_rings; i++) {
                err = blkfront_setup_indirect(&info->rinfo[i]);
                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, binfo, 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 (i = 0; i < info->nr_rings; i++)
                kick_pending_request_queues(&info->rinfo[i]);

        device_add_disk(&info->xbdev->dev, info->gd);

        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;
        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;
                /* Missed the backend's Closing state -- fallthrough */
        case XenbusStateClosing:
                if (info)
                        blkfront_closing(info);
                break;
        }
}

static int blkfront_remove(struct xenbus_device *xbdev)
{
        struct blkfront_info *info = dev_get_drvdata(&xbdev->dev);
        struct block_device *bdev = NULL;
        struct gendisk *disk;

        dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);

        blkif_free(info, 0);

        mutex_lock(&info->mutex);

        disk = info->gd;
        if (disk)
                bdev = bdget_disk(disk, 0);

        info->xbdev = NULL;
        mutex_unlock(&info->mutex);

        if (!bdev) {
                kfree(info);
                return 0;
        }

        /*
         * The xbdev was removed before we reached the Closed
         * state. See if it's safe to remove the disk. If the bdev
         * isn't closed yet, we let release take care of it.
         */

        mutex_lock(&bdev->bd_mutex);
        info = disk->private_data;

        dev_warn(disk_to_dev(disk),
                 "%s was hot-unplugged, %d stale handles\n",
                 xbdev->nodename, bdev->bd_openers);

        if (info && !bdev->bd_openers) {
                xlvbd_release_gendisk(info);
                disk->private_data = NULL;
                kfree(info);
        }

        mutex_unlock(&bdev->bd_mutex);
        bdput(bdev);

        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 int blkif_open(struct block_device *bdev, fmode_t mode)
{
        struct gendisk *disk = bdev->bd_disk;
        struct blkfront_info *info;
        int err = 0;

        mutex_lock(&blkfront_mutex);

        info = disk->private_data;
        if (!info) {
                /* xbdev gone */
                err = -ERESTARTSYS;
                goto out;
        }

        mutex_lock(&info->mutex);

        if (!info->gd)
                /* xbdev is closed */
                err = -ERESTARTSYS;

        mutex_unlock(&info->mutex);

out:
        mutex_unlock(&blkfront_mutex);
        return err;
}

static void blkif_release(struct gendisk *disk, fmode_t mode)
{
        struct blkfront_info *info = disk->private_data;
        struct block_device *bdev;
        struct xenbus_device *xbdev;

        mutex_lock(&blkfront_mutex);

        bdev = bdget_disk(disk, 0);

        if (!bdev) {
                WARN(1, "Block device %s yanked out from us!\n", disk->disk_name);
                goto out_mutex;
        }
        if (bdev->bd_openers)
                goto out;

        /*
         * Check if we have been instructed to close. We will have
         * deferred this request, because the bdev was still open.
         */

        mutex_lock(&info->mutex);
        xbdev = info->xbdev;

        if (xbdev && xbdev->state == XenbusStateClosing) {
                /* pending switch to state closed */
                dev_info(disk_to_dev(bdev->bd_disk), "releasing disk\n");
                xlvbd_release_gendisk(info);
                xenbus_frontend_closed(info->xbdev);
        }

        mutex_unlock(&info->mutex);

        if (!xbdev) {
                /* sudden device removal */
                dev_info(disk_to_dev(bdev->bd_disk), "releasing disk\n");
                xlvbd_release_gendisk(info);
                disk->private_data = NULL;
                kfree(info);
        }

out:
        bdput(bdev);
out_mutex:
        mutex_unlock(&blkfront_mutex);
}

static const struct block_device_operations xlvbd_block_fops =
{
        .owner = THIS_MODULE,
        .open = blkif_open,
        .release = blkif_release,
        .getgeo = blkif_getgeo,
        .ioctl = blkif_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 int __init xlblk_init(void)
{
        int ret;
        int nr_cpus = num_online_cpus();

        if (!xen_domain())
                return -ENODEV;

        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;
        }

        if (!xen_has_pv_disk_devices())
                return -ENODEV;

        if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
                printk(KERN_WARNING "xen_blk: can't get major %d with name %s\n",
                       XENVBD_MAJOR, DEV_NAME);
                return -ENODEV;
        }

        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)
{
        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");