Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild

[mirror_ubuntu-bionic-kernel.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/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 void add_id_to_freelist(struct blkfront_info *info,
                               unsigned long id)
{
        info->shadow[id].req.u.rw.id  = info->shadow_free;
        info->shadow[id].request = NULL;
        info->shadow_free = id;
}

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 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;

        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);
        }
        err = -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;

        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 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_sync(&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_sync(&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;
                req  = info->shadow[id].request;

                if (bret->operation != BLKIF_OP_DISCARD)
                        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_DISCARD:
                        if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
                                struct request_queue *rq = info->rq;
                                printk(KERN_WARNING "blkfront: %s: discard op failed\n",
                                           info->gd->disk_name);
                                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: write %s op failed\n",
                                       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
                                       "barrier" :  "flush disk cache",
                                       info->gd->disk_name);
                                error = -EOPNOTSUPP;
                        }
                        if (unlikely(bret->status == BLKIF_RSP_ERROR &&
                                     info->shadow[id].req.u.rw.nr_segments == 0)) {
                                printk(KERN_WARNING "blkfront: %s: empty write %s op failed\n",
                                       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
                                       "barrier" :  "flush disk cache",
                                       info->gd->disk_name);
                                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,
                                        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_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;
}

/**
 * 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;
                }
        }

        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;
}

/**
 * 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_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;
}

/**
 * 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 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)
{
        return xenbus_unregister_driver(&blkfront_driver);
}
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");