Linux 2.6.33-rc6

[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/hdreg.h>
#include <linux/cdrom.h>
#include <linux/module.h>
#include <linux/scatterlist.h>

#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/grant_table.h>
#include <xen/events.h>
#include <xen/page.h>

#include <xen/interface/grant_table.h>
#include <xen/interface/io/blkif.h>
#include <xen/interface/io/protocols.h>

#include <asm/xen/hypervisor.h>

enum blkif_state {
        BLKIF_STATE_DISCONNECTED,
        BLKIF_STATE_CONNECTED,
        BLKIF_STATE_SUSPENDED,
};

struct blk_shadow {
        struct blkif_request req;
        unsigned long request;
        unsigned long frame[BLKIF_MAX_SEGMENTS_PER_REQUEST];
};

static const struct block_device_operations xlvbd_block_fops;

#define BLK_RING_SIZE __RING_SIZE((struct blkif_sring *)0, PAGE_SIZE)

/*
 * 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 xenbus_device *xbdev;
        struct gendisk *gd;
        int vdevice;
        blkif_vdev_t handle;
        enum blkif_state connected;
        int ring_ref;
        struct blkif_front_ring ring;
        struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        unsigned int evtchn, irq;
        struct request_queue *rq;
        struct work_struct work;
        struct gnttab_free_callback callback;
        struct blk_shadow shadow[BLK_RING_SIZE];
        unsigned long shadow_free;
        int feature_barrier;
        int is_ready;

        /**
         * The number of people holding this device open.  We won't allow a
         * hot-unplug unless this is 0.
         */
        int users;
};

static DEFINE_SPINLOCK(blkif_io_lock);

#define MAXIMUM_OUTSTANDING_BLOCK_REQS \
        (BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
#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 DEV_NAME        "xvd"   /* name in /dev */

static int get_id_from_freelist(struct blkfront_info *info)
{
        unsigned long free = info->shadow_free;
        BUG_ON(free >= BLK_RING_SIZE);
        info->shadow_free = info->shadow[free].req.id;
        info->shadow[free].req.id = 0x0fffffee; /* debug */
        return free;
}

static void add_id_to_freelist(struct blkfront_info *info,
                               unsigned long id)
{
        info->shadow[id].req.id  = info->shadow_free;
        info->shadow[id].request = 0;
        info->shadow_free = id;
}

static void blkif_restart_queue_callback(void *arg)
{
        struct blkfront_info *info = (struct blkfront_info *)arg;
        schedule_work(&info->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;
}

/*
 * blkif_queue_request
 *
 * request block io
 *
 * id: for guest use only.
 * operation: BLKIF_OP_{READ,WRITE,PROBE}
 * buffer: buffer to read/write into. this should be a
 *   virtual address in the guest os.
 */
static int blkif_queue_request(struct request *req)
{
        struct blkfront_info *info = req->rq_disk->private_data;
        unsigned long buffer_mfn;
        struct blkif_request *ring_req;
        unsigned long id;
        unsigned int fsect, lsect;
        int i, ref;
        grant_ref_t gref_head;
        struct scatterlist *sg;

        if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
                return 1;

        if (gnttab_alloc_grant_references(
                BLKIF_MAX_SEGMENTS_PER_REQUEST, &gref_head) < 0) {
                gnttab_request_free_callback(
                        &info->callback,
                        blkif_restart_queue_callback,
                        info,
                        BLKIF_MAX_SEGMENTS_PER_REQUEST);
                return 1;
        }

        /* Fill out a communications ring structure. */
        ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
        id = get_id_from_freelist(info);
        info->shadow[id].request = (unsigned long)req;

        ring_req->id = id;
        ring_req->sector_number = (blkif_sector_t)blk_rq_pos(req);
        ring_req->handle = info->handle;

        ring_req->operation = rq_data_dir(req) ?
                BLKIF_OP_WRITE : BLKIF_OP_READ;
        if (blk_barrier_rq(req))
                ring_req->operation = BLKIF_OP_WRITE_BARRIER;

        ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
        BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);

        for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
                buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
                fsect = sg->offset >> 9;
                lsect = fsect + (sg->length >> 9) - 1;
                /* install a grant reference. */
                ref = gnttab_claim_grant_reference(&gref_head);
                BUG_ON(ref == -ENOSPC);

                gnttab_grant_foreign_access_ref(
                                ref,
                                info->xbdev->otherend_id,
                                buffer_mfn,
                                rq_data_dir(req) );

                info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
                ring_req->seg[i] =
                                (struct blkif_request_segment) {
                                        .gref       = ref,
                                        .first_sect = fsect,
                                        .last_sect  = lsect };
        }

        info->ring.req_prod_pvt++;

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

        gnttab_free_grant_references(gref_head);

        return 0;
}


static inline void flush_requests(struct blkfront_info *info)
{
        int notify;

        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->ring, notify);

        if (notify)
                notify_remote_via_irq(info->irq);
}

/*
 * do_blkif_request
 *  read a block; request is in a request queue
 */
static void do_blkif_request(struct request_queue *rq)
{
        struct blkfront_info *info = NULL;
        struct request *req;
        int queued;

        pr_debug("Entered do_blkif_request\n");

        queued = 0;

        while ((req = blk_peek_request(rq)) != NULL) {
                info = req->rq_disk->private_data;

                if (RING_FULL(&info->ring))
                        goto wait;

                blk_start_request(req);

                if (!blk_fs_request(req)) {
                        __blk_end_request_all(req, -EIO);
                        continue;
                }

                pr_debug("do_blk_req %p: cmd %p, sec %lx, "
                         "(%u/%u) buffer:%p [%s]\n",
                         req, req->cmd, (unsigned long)blk_rq_pos(req),
                         blk_rq_cur_sectors(req), blk_rq_sectors(req),
                         req->buffer, rq_data_dir(req) ? "write" : "read");

                if (blkif_queue_request(req)) {
                        blk_requeue_request(rq, req);
wait:
                        /* Avoid pointless unplugs. */
                        blk_stop_queue(rq);
                        break;
                }

                queued++;
        }

        if (queued != 0)
                flush_requests(info);
}

static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
{
        struct request_queue *rq;

        rq = blk_init_queue(do_blkif_request, &blkif_io_lock);
        if (rq == NULL)
                return -1;

        queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);

        /* Hard sector size and max sectors impersonate the equiv. hardware. */
        blk_queue_logical_block_size(rq, sector_size);
        blk_queue_max_sectors(rq, 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_phys_segments(rq, BLKIF_MAX_SEGMENTS_PER_REQUEST);
        blk_queue_max_hw_segments(rq, BLKIF_MAX_SEGMENTS_PER_REQUEST);

        /* 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);

        gd->queue = rq;

        return 0;
}


static int xlvbd_barrier(struct blkfront_info *info)
{
        int err;

        err = blk_queue_ordered(info->rq,
                                info->feature_barrier ? QUEUE_ORDERED_DRAIN : QUEUE_ORDERED_NONE,
                                NULL);

        if (err)
                return err;

        printk(KERN_INFO "blkfront: %s: barriers %s\n",
               info->gd->disk_name,
               info->feature_barrier ? "enabled" : "disabled");
        return 0;
}


static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
                               struct blkfront_info *info,
                               u16 vdisk_info, u16 sector_size)
{
        struct gendisk *gd;
        int nr_minors = 1;
        int err = -ENODEV;
        unsigned int offset;
        int minor;
        int nr_parts;

        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)) {
                minor = BLKIF_MINOR(info->vdevice);
                nr_parts = PARTS_PER_DISK;
        } else {
                minor = BLKIF_MINOR_EXT(info->vdevice);
                nr_parts = PARTS_PER_EXT_DISK;
        }

        if ((minor % nr_parts) == 0)
                nr_minors = nr_parts;

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

        offset = minor / nr_parts;

        if (nr_minors > 1) {
                if (offset < 26)
                        sprintf(gd->disk_name, "%s%c", DEV_NAME, 'a' + offset);
                else
                        sprintf(gd->disk_name, "%s%c%c", DEV_NAME,
                                'a' + ((offset / 26)-1), 'a' + (offset % 26));
        } else {
                if (offset < 26)
                        sprintf(gd->disk_name, "%s%c%d", DEV_NAME,
                                'a' + offset,
                                minor & (nr_parts - 1));
                else
                        sprintf(gd->disk_name, "%s%c%c%d", DEV_NAME,
                                'a' + ((offset / 26) - 1),
                                'a' + (offset % 26),
                                minor & (nr_parts - 1));
        }

        gd->major = XENVBD_MAJOR;
        gd->first_minor = minor;
        gd->fops = &xlvbd_block_fops;
        gd->private_data = info;
        gd->driverfs_dev = &(info->xbdev->dev);
        set_capacity(gd, capacity);

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

        info->rq = gd->queue;
        info->gd = gd;

        if (info->feature_barrier)
                xlvbd_barrier(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;

 out:
        return err;
}

static void kick_pending_request_queues(struct blkfront_info *info)
{
        if (!RING_FULL(&info->ring)) {
                /* Re-enable calldowns. */
                blk_start_queue(info->rq);
                /* Kick things off immediately. */
                do_blkif_request(info->rq);
        }
}

static void blkif_restart_queue(struct work_struct *work)
{
        struct blkfront_info *info = container_of(work, struct blkfront_info, work);

        spin_lock_irq(&blkif_io_lock);
        if (info->connected == BLKIF_STATE_CONNECTED)
                kick_pending_request_queues(info);
        spin_unlock_irq(&blkif_io_lock);
}

static void blkif_free(struct blkfront_info *info, int suspend)
{
        /* Prevent new requests being issued until we fix things up. */
        spin_lock_irq(&blkif_io_lock);
        info->connected = suspend ?
                BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
        /* No more blkif_request(). */
        if (info->rq)
                blk_stop_queue(info->rq);
        /* No more gnttab callback work. */
        gnttab_cancel_free_callback(&info->callback);
        spin_unlock_irq(&blkif_io_lock);

        /* Flush gnttab callback work. Must be done with no locks held. */
        flush_scheduled_work();

        /* Free resources associated with old device channel. */
        if (info->ring_ref != GRANT_INVALID_REF) {
                gnttab_end_foreign_access(info->ring_ref, 0,
                                          (unsigned long)info->ring.sring);
                info->ring_ref = GRANT_INVALID_REF;
                info->ring.sring = NULL;
        }
        if (info->irq)
                unbind_from_irqhandler(info->irq, info);
        info->evtchn = info->irq = 0;

}

static void blkif_completion(struct blk_shadow *s)
{
        int i;
        for (i = 0; i < s->req.nr_segments; i++)
                gnttab_end_foreign_access(s->req.seg[i].gref, 0, 0UL);
}

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_info *info = (struct blkfront_info *)dev_id;
        int error;

        spin_lock_irqsave(&blkif_io_lock, flags);

        if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
                spin_unlock_irqrestore(&blkif_io_lock, flags);
                return IRQ_HANDLED;
        }

 again:
        rp = info->ring.sring->rsp_prod;
        rmb(); /* Ensure we see queued responses up to 'rp'. */

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

                bret = RING_GET_RESPONSE(&info->ring, i);
                id   = bret->id;
                req  = (struct request *)info->shadow[id].request;

                blkif_completion(&info->shadow[id]);

                add_id_to_freelist(info, id);

                error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
                switch (bret->operation) {
                case BLKIF_OP_WRITE_BARRIER:
                        if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
                                printk(KERN_WARNING "blkfront: %s: write barrier op failed\n",
                                       info->gd->disk_name);
                                error = -EOPNOTSUPP;
                                info->feature_barrier = 0;
                                xlvbd_barrier(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_end_request_all(req, error);
                        break;
                default:
                        BUG();
                }
        }

        info->ring.rsp_cons = i;

        if (i != info->ring.req_prod_pvt) {
                int more_to_do;
                RING_FINAL_CHECK_FOR_RESPONSES(&info->ring, more_to_do);
                if (more_to_do)
                        goto again;
        } else
                info->ring.sring->rsp_event = i + 1;

        kick_pending_request_queues(info);

        spin_unlock_irqrestore(&blkif_io_lock, flags);

        return IRQ_HANDLED;
}


static int setup_blkring(struct xenbus_device *dev,
                         struct blkfront_info *info)
{
        struct blkif_sring *sring;
        int err;

        info->ring_ref = GRANT_INVALID_REF;

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

        sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);

        err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
        if (err < 0) {
                free_page((unsigned long)sring);
                info->ring.sring = NULL;
                goto fail;
        }
        info->ring_ref = err;

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

        err = bind_evtchn_to_irqhandler(info->evtchn,
                                        blkif_interrupt,
                                        IRQF_SAMPLE_RANDOM, "blkif", info);
        if (err <= 0) {
                xenbus_dev_fatal(dev, err,
                                 "bind_evtchn_to_irqhandler failed");
                goto fail;
        }
        info->irq = err;

        return 0;
fail:
        blkif_free(info, 0);
        return err;
}


/* Common code used when first setting up, and when resuming. */
static int talk_to_backend(struct xenbus_device *dev,
                           struct blkfront_info *info)
{
        const char *message = NULL;
        struct xenbus_transaction xbt;
        int err;

        /* Create shared ring, alloc event channel. */
        err = setup_blkring(dev, info);
        if (err)
                goto out;

again:
        err = xenbus_transaction_start(&xbt);
        if (err) {
                xenbus_dev_fatal(dev, err, "starting transaction");
                goto destroy_blkring;
        }

        err = xenbus_printf(xbt, dev->nodename,
                            "ring-ref", "%u", info->ring_ref);
        if (err) {
                message = "writing ring-ref";
                goto abort_transaction;
        }
        err = xenbus_printf(xbt, dev->nodename,
                            "event-channel", "%u", info->evtchn);
        if (err) {
                message = "writing event-channel";
                goto abort_transaction;
        }
        err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
                            XEN_IO_PROTO_ABI_NATIVE);
        if (err) {
                message = "writing protocol";
                goto abort_transaction;
        }

        err = xenbus_transaction_end(xbt, 0);
        if (err) {
                if (err == -EAGAIN)
                        goto again;
                xenbus_dev_fatal(dev, err, "completing transaction");
                goto destroy_blkring;
        }

        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);
 out:
        return err;
}


/**
 * 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, i;
        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;
                }
        }

        info = kzalloc(sizeof(*info), GFP_KERNEL);
        if (!info) {
                xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");
                return -ENOMEM;
        }

        info->xbdev = dev;
        info->vdevice = vdevice;
        info->connected = BLKIF_STATE_DISCONNECTED;
        INIT_WORK(&info->work, blkif_restart_queue);

        for (i = 0; i < BLK_RING_SIZE; i++)
                info->shadow[i].req.id = i+1;
        info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;

        /* 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);

        err = talk_to_backend(dev, info);
        if (err) {
                kfree(info);
                dev_set_drvdata(&dev->dev, NULL);
                return err;
        }

        return 0;
}


static int blkif_recover(struct blkfront_info *info)
{
        int i;
        struct blkif_request *req;
        struct blk_shadow *copy;
        int j;

        /* Stage 1: Make a safe copy of the shadow state. */
        copy = kmalloc(sizeof(info->shadow),
                       GFP_NOIO | __GFP_REPEAT | __GFP_HIGH);
        if (!copy)
                return -ENOMEM;
        memcpy(copy, info->shadow, sizeof(info->shadow));

        /* Stage 2: Set up free list. */
        memset(&info->shadow, 0, sizeof(info->shadow));
        for (i = 0; i < BLK_RING_SIZE; i++)
                info->shadow[i].req.id = i+1;
        info->shadow_free = info->ring.req_prod_pvt;
        info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;

        /* Stage 3: Find pending requests and requeue them. */
        for (i = 0; i < BLK_RING_SIZE; i++) {
                /* Not in use? */
                if (copy[i].request == 0)
                        continue;

                /* Grab a request slot and copy shadow state into it. */
                req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
                *req = copy[i].req;

                /* We get a new request id, and must reset the shadow state. */
                req->id = get_id_from_freelist(info);
                memcpy(&info->shadow[req->id], &copy[i], sizeof(copy[i]));

                /* Rewrite any grant references invalidated by susp/resume. */
                for (j = 0; j < req->nr_segments; j++)
                        gnttab_grant_foreign_access_ref(
                                req->seg[j].gref,
                                info->xbdev->otherend_id,
                                pfn_to_mfn(info->shadow[req->id].frame[j]),
                                rq_data_dir(
                                        (struct request *)
                                        info->shadow[req->id].request));
                info->shadow[req->id].req = *req;

                info->ring.req_prod_pvt++;
        }

        kfree(copy);

        xenbus_switch_state(info->xbdev, XenbusStateConnected);

        spin_lock_irq(&blkif_io_lock);

        /* Now safe for us to use the shared ring */
        info->connected = BLKIF_STATE_CONNECTED;

        /* Send off requeued requests */
        flush_requests(info);

        /* Kick any other new requests queued since we resumed */
        kick_pending_request_queues(info);

        spin_unlock_irq(&blkif_io_lock);

        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;

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

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

        err = talk_to_backend(dev, info);
        if (info->connected == BLKIF_STATE_SUSPENDED && !err)
                err = blkif_recover(info);

        return err;
}


/*
 * 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 binfo;
        int err;

        if ((info->connected == BLKIF_STATE_CONNECTED) ||
            (info->connected == BLKIF_STATE_SUSPENDED) )
                return;

        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;
        }

        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                            "feature-barrier", "%lu", &info->feature_barrier,
                            NULL);
        if (err)
                info->feature_barrier = 0;

        err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
        if (err) {
                xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
                                 info->xbdev->otherend);
                return;
        }

        xenbus_switch_state(info->xbdev, XenbusStateConnected);

        /* Kick pending requests. */
        spin_lock_irq(&blkif_io_lock);
        info->connected = BLKIF_STATE_CONNECTED;
        kick_pending_request_queues(info);
        spin_unlock_irq(&blkif_io_lock);

        add_disk(info->gd);

        info->is_ready = 1;
}

/**
 * Handle the change of state of the backend to Closing.  We must delete our
 * device-layer structures now, to ensure that writes are flushed through to
 * the backend.  Once is this done, we can switch to Closed in
 * acknowledgement.
 */
static void blkfront_closing(struct xenbus_device *dev)
{
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);
        unsigned long flags;

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

        if (info->rq == NULL)
                goto out;

        spin_lock_irqsave(&blkif_io_lock, flags);

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

        /* No more gnttab callback work. */
        gnttab_cancel_free_callback(&info->callback);
        spin_unlock_irqrestore(&blkif_io_lock, flags);

        /* Flush gnttab callback work. Must be done with no locks held. */
        flush_scheduled_work();

        blk_cleanup_queue(info->rq);
        info->rq = NULL;

        del_gendisk(info->gd);

 out:
        xenbus_frontend_closed(dev);
}

/**
 * Callback received when the backend's state changes.
 */
static void backend_changed(struct xenbus_device *dev,
                            enum xenbus_state backend_state)
{
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);
        struct block_device *bd;

        dev_dbg(&dev->dev, "blkfront:backend_changed.\n");

        switch (backend_state) {
        case XenbusStateInitialising:
        case XenbusStateInitWait:
        case XenbusStateInitialised:
        case XenbusStateUnknown:
        case XenbusStateClosed:
                break;

        case XenbusStateConnected:
                blkfront_connect(info);
                break;

        case XenbusStateClosing:
                if (info->gd == NULL) {
                        xenbus_frontend_closed(dev);
                        break;
                }
                bd = bdget_disk(info->gd, 0);
                if (bd == NULL)
                        xenbus_dev_fatal(dev, -ENODEV, "bdget failed");

                mutex_lock(&bd->bd_mutex);
                if (info->users > 0)
                        xenbus_dev_error(dev, -EBUSY,
                                         "Device in use; refusing to close");
                else
                        blkfront_closing(dev);
                mutex_unlock(&bd->bd_mutex);
                bdput(bd);
                break;
        }
}

static int blkfront_remove(struct xenbus_device *dev)
{
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);

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

        blkif_free(info, 0);

        kfree(info);

        return 0;
}

static int blkfront_is_ready(struct xenbus_device *dev)
{
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);

        return info->is_ready;
}

static int blkif_open(struct block_device *bdev, fmode_t mode)
{
        struct blkfront_info *info = bdev->bd_disk->private_data;
        info->users++;
        return 0;
}

static int blkif_release(struct gendisk *disk, fmode_t mode)
{
        struct blkfront_info *info = disk->private_data;
        info->users--;
        if (info->users == 0) {
                /* Check whether we have been instructed to close.  We will
                   have ignored this request initially, as the device was
                   still mounted. */
                struct xenbus_device *dev = info->xbdev;
                enum xenbus_state state = xenbus_read_driver_state(dev->otherend);

                if (state == XenbusStateClosing && info->is_ready)
                        blkfront_closing(dev);
        }
        return 0;
}

static const struct block_device_operations xlvbd_block_fops =
{
        .owner = THIS_MODULE,
        .open = blkif_open,
        .release = blkif_release,
        .getgeo = blkif_getgeo,
        .locked_ioctl = blkif_ioctl,
};


static struct xenbus_device_id blkfront_ids[] = {
        { "vbd" },
        { "" }
};

static struct xenbus_driver blkfront = {
        .name = "vbd",
        .owner = THIS_MODULE,
        .ids = blkfront_ids,
        .probe = blkfront_probe,
        .remove = blkfront_remove,
        .resume = blkfront_resume,
        .otherend_changed = backend_changed,
        .is_ready = blkfront_is_ready,
};

static int __init xlblk_init(void)
{
        if (!xen_domain())
                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;
        }

        return xenbus_register_frontend(&blkfront);
}
module_init(xlblk_init);


static void __exit xlblk_exit(void)
{
        return xenbus_unregister_driver(&blkfront);
}
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");