xen-blkfront.c

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/*
 * 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/slab.h>
#include <linux/mutex.h>
#include <linux/scatterlist.h>
#include <linux/bitmap.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>

enum blkif_state {
    BLKIF_STATE_DISCONNECTED,
    BLKIF_STATE_CONNECTED,
    BLKIF_STATE_SUSPENDED,
};

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

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

#define BLK_RING_SIZE __CONST_RING_SIZE(blkif, 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
{
    spinlock_t io_lock;
    struct mutex mutex;
    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;
    unsigned int feature_flush;
    unsigned int flush_op;
    unsigned int feature_discard:1;
    unsigned int feature_secdiscard:1;
    unsigned int discard_granularity;
    unsigned int discard_alignment;
    int is_ready;
};

static unsigned int nr_minors;
static unsigned long *minors;
static DEFINE_SPINLOCK(minor_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 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 */

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.u.rw.id;
    info->shadow[free].req.u.rw.id = 0x0fffffee; /* debug */
    return free;
}

static int add_id_to_freelist(struct blkfront_info *info,
                   unsigned long id)
{
    if (info->shadow[id].req.u.rw.id != id)
        return -EINVAL;
    if (info->shadow[id].request == NULL)
        return -EINVAL;
    info->shadow[id].req.u.rw.id  = info->shadow_free;
    info->shadow[id].request = NULL;
    info->shadow_free = id;
    return 0;
}

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_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;
}

/*
 * 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_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 = req;

    ring_req->u.rw.id = id;
    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->cmd_flags & (REQ_FLUSH | 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.)
         */
        ring_req->operation = info->flush_op;
    }

    if (unlikely(req->cmd_flags & (REQ_DISCARD | REQ_SECURE))) {
        /* id, sector_number and handle are set above. */
        ring_req->operation = BLKIF_OP_DISCARD;
        ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
        if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
            ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
        else
            ring_req->u.discard.flag = 0;
    } else {
        ring_req->u.rw.nr_segments = blk_rq_map_sg(req->q, req,
                               info->sg);
        BUG_ON(ring_req->u.rw.nr_segments >
               BLKIF_MAX_SEGMENTS_PER_REQUEST);

        for_each_sg(info->sg, sg, ring_req->u.rw.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->u.rw.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 ((req->cmd_type != REQ_TYPE_FS) ||
            ((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) &&
            !info->flush_op)) {
            __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;
    struct blkfront_info *info = gd->private_data;

    rq = blk_init_queue(do_blkif_request, &info->io_lock);
    if (rq == NULL)
        return -1;

    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_SECDISCARD, rq);
    }

    /* Hard sector size and max sectors impersonate the equiv. hardware. */
    blk_queue_logical_block_size(rq, sector_size);
    blk_queue_max_hw_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_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 void xlvbd_flush(struct blkfront_info *info)
{
    blk_queue_flush(info->rq, info->feature_flush);
    printk(KERN_INFO "blkfront: %s: %s: %s\n",
           info->gd->disk_name,
           info->flush_op == BLKIF_OP_WRITE_BARRIER ?
        "barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
        "flush diskcache" : "barrier or flush"),
           info->feature_flush ? "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)
{
    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;
    gd->driverfs_dev = &(info->xbdev->dev);
    set_capacity(gd, capacity);

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

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

    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;
    unsigned long flags;

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

    spin_lock_irqsave(&info->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(&info->io_lock, flags);

    /* Flush gnttab callback work. Must be done with no locks held. */
    flush_work(&info->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);
    info->rq = NULL;

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

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(&info->io_lock);
    if (info->connected == BLKIF_STATE_CONNECTED)
        kick_pending_request_queues(info);
    spin_unlock_irq(&info->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(&info->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(&info->io_lock);

    /* Flush gnttab callback work. Must be done with no locks held. */
    flush_work(&info->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;
    /* Do not let BLKIF_OP_DISCARD as nr_segment is in the same place
     * flag. */
    for (i = 0; i < s->req.u.rw.nr_segments; i++)
        gnttab_end_foreign_access(s->req.u.rw.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(&info->io_lock, flags);

    if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
        spin_unlock_irqrestore(&info->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;
        /*
         * 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) {
            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  = info->shadow[id].request;

        if (bret->operation != BLKIF_OP_DISCARD)
            blkif_completion(&info->shadow[id]);

        if (add_id_to_freelist(info, 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_SECDISCARD, rq);
            }
            __blk_end_request_all(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 &&
                     info->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_flush = 0;
                info->flush_op = 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_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(&info->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, 0,
                    "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_blkback(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;
}

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;
        }
    }

    if (xen_hvm_domain()) {
        char *type;
        int len;
        /* no unplug has been done: do not hook devices != xen vbds */
        if (xen_platform_pci_unplug & XEN_UNPLUG_UNNECESSARY) {
            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",
                        __FUNCTION__, 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;
    }

    mutex_init(&info->mutex);
    spin_lock_init(&info->io_lock);
    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.u.rw.id = i+1;
    info->shadow[BLK_RING_SIZE-1].req.u.rw.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_blkback(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.u.rw.id = i+1;
    info->shadow_free = info->ring.req_prod_pvt;
    info->shadow[BLK_RING_SIZE-1].req.u.rw.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)
            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->u.rw.id = get_id_from_freelist(info);
        memcpy(&info->shadow[req->u.rw.id], &copy[i], sizeof(copy[i]));

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

        info->ring.req_prod_pvt++;
    }

    kfree(copy);

    xenbus_switch_state(info->xbdev, XenbusStateConnected);

    spin_lock_irq(&info->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(&info->io_lock);

    return 0;
}

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

    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;
    char *type;
    unsigned int discard_granularity;
    unsigned int discard_alignment;
    unsigned int discard_secure;

    type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
    if (IS_ERR(type))
        return;

    info->feature_secdiscard = 0;
    if (strncmp(type, "phy", 3) == 0) {
        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
            "discard-granularity", "%u", &discard_granularity,
            "discard-alignment", "%u", &discard_alignment,
            NULL);
        if (!err) {
            info->feature_discard = 1;
            info->discard_granularity = discard_granularity;
            info->discard_alignment = discard_alignment;
        }
        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                "discard-secure", "%d", &discard_secure,
                NULL);
        if (!err)
            info->feature_secdiscard = discard_secure;

    } else if (strncmp(type, "file", 4) == 0)
        info->feature_discard = 1;

    kfree(type);
}

/*
 * 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;
    int barrier, flush, discard;

    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);

        /* fall through */
    case BLKIF_STATE_SUSPENDED:
        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;
    }

    info->feature_flush = 0;
    info->flush_op = 0;

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

    /*
     * 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 && barrier) {
        info->feature_flush = REQ_FLUSH | REQ_FUA;
        info->flush_op = BLKIF_OP_WRITE_BARRIER;
    }
    /*
     * And if there is "feature-flush-cache" use that above
     * barriers.
     */
    err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                "feature-flush-cache", "%d", &flush,
                NULL);

    if (!err && flush) {
        info->feature_flush = REQ_FLUSH;
        info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
    }

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

    if (!err && discard)
        blkfront_setup_discard(info);

    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(&info->io_lock);
    info->connected = BLKIF_STATE_CONNECTED;
    kick_pending_request_queues(info);
    spin_unlock_irq(&info->io_lock);

    add_disk(info->gd);

    info->is_ready = 1;
}

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 XenbusStateInitialising:
    case XenbusStateInitWait:
    case XenbusStateInitialised:
    case XenbusStateReconfiguring:
    case XenbusStateReconfigured:
    case XenbusStateUnknown:
    case XenbusStateClosed:
        break;

    case XenbusStateConnected:
        blkfront_connect(info);
        break;

    case XenbusStateClosing:
        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 int 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->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);
    mutex_unlock(&blkfront_mutex);
    return 0;
}

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 DEFINE_XENBUS_DRIVER(blkfront, ,
    .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;

    if (!xen_domain())
        return -ENODEV;

    if (xen_hvm_domain() && !xen_platform_pci_unplug)
        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");