virtio_blk.c

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//#define DEBUG
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/virtio.h>
#include <linux/virtio_blk.h>
#include <linux/scatterlist.h>
#include <linux/string_helpers.h>
#include <scsi/scsi_cmnd.h>
#include <linux/idr.h>

#define PART_BITS 4

static bool use_bio;
module_param(use_bio, bool, S_IRUGO);

static int major;
static DEFINE_IDA(vd_index_ida);

struct workqueue_struct *virtblk_wq;

struct virtio_blk
{
    struct virtio_device *vdev;
    struct virtqueue *vq;
    wait_queue_head_t queue_wait;

    /* The disk structure for the kernel. */
    struct gendisk *disk;

    mempool_t *pool;

    /* Process context for config space updates */
    struct work_struct config_work;

    /* Lock for config space updates */
    struct mutex config_lock;

    /* enable config space updates */
    bool config_enable;

    /* What host tells us, plus 2 for header & tailer. */
    unsigned int sg_elems;

    /* Ida index - used to track minor number allocations. */
    int index;

    /* Scatterlist: can be too big for stack. */
    struct scatterlist sg[/*sg_elems*/];
};

struct virtblk_req
{
    struct request *req;
    struct bio *bio;
    struct virtio_blk_outhdr out_hdr;
    struct virtio_scsi_inhdr in_hdr;
    struct work_struct work;
    struct virtio_blk *vblk;
    int flags;
    u8 status;
    struct scatterlist sg[];
};

enum {
    VBLK_IS_FLUSH       = 1,
    VBLK_REQ_FLUSH      = 2,
    VBLK_REQ_DATA       = 4,
    VBLK_REQ_FUA        = 8,
};

static inline int virtblk_result(struct virtblk_req *vbr)
{
    switch (vbr->status) {
    case VIRTIO_BLK_S_OK:
        return 0;
    case VIRTIO_BLK_S_UNSUPP:
        return -ENOTTY;
    default:
        return -EIO;
    }
}

static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk,
                            gfp_t gfp_mask)
{
    struct virtblk_req *vbr;

    vbr = mempool_alloc(vblk->pool, gfp_mask);
    if (!vbr)
        return NULL;

    vbr->vblk = vblk;
    if (use_bio)
        sg_init_table(vbr->sg, vblk->sg_elems);

    return vbr;
}

static void virtblk_add_buf_wait(struct virtio_blk *vblk,
                 struct virtblk_req *vbr,
                 unsigned long out,
                 unsigned long in)
{
    DEFINE_WAIT(wait);

    for (;;) {
        prepare_to_wait_exclusive(&vblk->queue_wait, &wait,
                      TASK_UNINTERRUPTIBLE);

        spin_lock_irq(vblk->disk->queue->queue_lock);
        if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr,
                      GFP_ATOMIC) < 0) {
            spin_unlock_irq(vblk->disk->queue->queue_lock);
            io_schedule();
        } else {
            virtqueue_kick(vblk->vq);
            spin_unlock_irq(vblk->disk->queue->queue_lock);
            break;
        }

    }

    finish_wait(&vblk->queue_wait, &wait);
}

static inline void virtblk_add_req(struct virtblk_req *vbr,
                   unsigned int out, unsigned int in)
{
    struct virtio_blk *vblk = vbr->vblk;

    spin_lock_irq(vblk->disk->queue->queue_lock);
    if (unlikely(virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr,
                    GFP_ATOMIC) < 0)) {
        spin_unlock_irq(vblk->disk->queue->queue_lock);
        virtblk_add_buf_wait(vblk, vbr, out, in);
        return;
    }
    virtqueue_kick(vblk->vq);
    spin_unlock_irq(vblk->disk->queue->queue_lock);
}

static int virtblk_bio_send_flush(struct virtblk_req *vbr)
{
    unsigned int out = 0, in = 0;

    vbr->flags |= VBLK_IS_FLUSH;
    vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;
    vbr->out_hdr.sector = 0;
    vbr->out_hdr.ioprio = 0;
    sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
    sg_set_buf(&vbr->sg[out + in++], &vbr->status, sizeof(vbr->status));

    virtblk_add_req(vbr, out, in);

    return 0;
}

static int virtblk_bio_send_data(struct virtblk_req *vbr)
{
    struct virtio_blk *vblk = vbr->vblk;
    unsigned int num, out = 0, in = 0;
    struct bio *bio = vbr->bio;

    vbr->flags &= ~VBLK_IS_FLUSH;
    vbr->out_hdr.type = 0;
    vbr->out_hdr.sector = bio->bi_sector;
    vbr->out_hdr.ioprio = bio_prio(bio);

    sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));

    num = blk_bio_map_sg(vblk->disk->queue, bio, vbr->sg + out);

    sg_set_buf(&vbr->sg[num + out + in++], &vbr->status,
           sizeof(vbr->status));

    if (num) {
        if (bio->bi_rw & REQ_WRITE) {
            vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
            out += num;
        } else {
            vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
            in += num;
        }
    }

    virtblk_add_req(vbr, out, in);

    return 0;
}

static void virtblk_bio_send_data_work(struct work_struct *work)
{
    struct virtblk_req *vbr;

    vbr = container_of(work, struct virtblk_req, work);

    virtblk_bio_send_data(vbr);
}

static void virtblk_bio_send_flush_work(struct work_struct *work)
{
    struct virtblk_req *vbr;

    vbr = container_of(work, struct virtblk_req, work);

    virtblk_bio_send_flush(vbr);
}

static inline void virtblk_request_done(struct virtblk_req *vbr)
{
    struct virtio_blk *vblk = vbr->vblk;
    struct request *req = vbr->req;
    int error = virtblk_result(vbr);

    if (req->cmd_type == REQ_TYPE_BLOCK_PC) {
        req->resid_len = vbr->in_hdr.residual;
        req->sense_len = vbr->in_hdr.sense_len;
        req->errors = vbr->in_hdr.errors;
    } else if (req->cmd_type == REQ_TYPE_SPECIAL) {
        req->errors = (error != 0);
    }

    __blk_end_request_all(req, error);
    mempool_free(vbr, vblk->pool);
}

static inline void virtblk_bio_flush_done(struct virtblk_req *vbr)
{
    struct virtio_blk *vblk = vbr->vblk;

    if (vbr->flags & VBLK_REQ_DATA) {
        /* Send out the actual write data */
        INIT_WORK(&vbr->work, virtblk_bio_send_data_work);
        queue_work(virtblk_wq, &vbr->work);
    } else {
        bio_endio(vbr->bio, virtblk_result(vbr));
        mempool_free(vbr, vblk->pool);
    }
}

static inline void virtblk_bio_data_done(struct virtblk_req *vbr)
{
    struct virtio_blk *vblk = vbr->vblk;

    if (unlikely(vbr->flags & VBLK_REQ_FUA)) {
        /* Send out a flush before end the bio */
        vbr->flags &= ~VBLK_REQ_DATA;
        INIT_WORK(&vbr->work, virtblk_bio_send_flush_work);
        queue_work(virtblk_wq, &vbr->work);
    } else {
        bio_endio(vbr->bio, virtblk_result(vbr));
        mempool_free(vbr, vblk->pool);
    }
}

static inline void virtblk_bio_done(struct virtblk_req *vbr)
{
    if (unlikely(vbr->flags & VBLK_IS_FLUSH))
        virtblk_bio_flush_done(vbr);
    else
        virtblk_bio_data_done(vbr);
}

static void virtblk_done(struct virtqueue *vq)
{
    struct virtio_blk *vblk = vq->vdev->priv;
    bool bio_done = false, req_done = false;
    struct virtblk_req *vbr;
    unsigned long flags;
    unsigned int len;

    spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
    do {
        virtqueue_disable_cb(vq);
        while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
            if (vbr->bio) {
                virtblk_bio_done(vbr);
                bio_done = true;
            } else {
                virtblk_request_done(vbr);
                req_done = true;
            }
        }
    } while (!virtqueue_enable_cb(vq));
    /* In case queue is stopped waiting for more buffers. */
    if (req_done)
        blk_start_queue(vblk->disk->queue);
    spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags);

    if (bio_done)
        wake_up(&vblk->queue_wait);
}

static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
           struct request *req)
{
    unsigned long num, out = 0, in = 0;
    struct virtblk_req *vbr;

    vbr = virtblk_alloc_req(vblk, GFP_ATOMIC);
    if (!vbr)
        /* When another request finishes we'll try again. */
        return false;

    vbr->req = req;
    vbr->bio = NULL;
    if (req->cmd_flags & REQ_FLUSH) {
        vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;
        vbr->out_hdr.sector = 0;
        vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
    } else {
        switch (req->cmd_type) {
        case REQ_TYPE_FS:
            vbr->out_hdr.type = 0;
            vbr->out_hdr.sector = blk_rq_pos(vbr->req);
            vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
            break;
        case REQ_TYPE_BLOCK_PC:
            vbr->out_hdr.type = VIRTIO_BLK_T_SCSI_CMD;
            vbr->out_hdr.sector = 0;
            vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
            break;
        case REQ_TYPE_SPECIAL:
            vbr->out_hdr.type = VIRTIO_BLK_T_GET_ID;
            vbr->out_hdr.sector = 0;
            vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
            break;
        default:
            /* We don't put anything else in the queue. */
            BUG();
        }
    }

    sg_set_buf(&vblk->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));

    /*
     * If this is a packet command we need a couple of additional headers.
     * Behind the normal outhdr we put a segment with the scsi command
     * block, and before the normal inhdr we put the sense data and the
     * inhdr with additional status information before the normal inhdr.
     */
    if (vbr->req->cmd_type == REQ_TYPE_BLOCK_PC)
        sg_set_buf(&vblk->sg[out++], vbr->req->cmd, vbr->req->cmd_len);

    num = blk_rq_map_sg(q, vbr->req, vblk->sg + out);

    if (vbr->req->cmd_type == REQ_TYPE_BLOCK_PC) {
        sg_set_buf(&vblk->sg[num + out + in++], vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
        sg_set_buf(&vblk->sg[num + out + in++], &vbr->in_hdr,
               sizeof(vbr->in_hdr));
    }

    sg_set_buf(&vblk->sg[num + out + in++], &vbr->status,
           sizeof(vbr->status));

    if (num) {
        if (rq_data_dir(vbr->req) == WRITE) {
            vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
            out += num;
        } else {
            vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
            in += num;
        }
    }

    if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr,
                  GFP_ATOMIC) < 0) {
        mempool_free(vbr, vblk->pool);
        return false;
    }

    return true;
}

static void virtblk_request(struct request_queue *q)
{
    struct virtio_blk *vblk = q->queuedata;
    struct request *req;
    unsigned int issued = 0;

    while ((req = blk_peek_request(q)) != NULL) {
        BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);

        /* If this request fails, stop queue and wait for something to
           finish to restart it. */
        if (!do_req(q, vblk, req)) {
            blk_stop_queue(q);
            break;
        }
        blk_start_request(req);
        issued++;
    }

    if (issued)
        virtqueue_kick(vblk->vq);
}

static void virtblk_make_request(struct request_queue *q, struct bio *bio)
{
    struct virtio_blk *vblk = q->queuedata;
    struct virtblk_req *vbr;

    BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems);

    vbr = virtblk_alloc_req(vblk, GFP_NOIO);
    if (!vbr) {
        bio_endio(bio, -ENOMEM);
        return;
    }

    vbr->bio = bio;
    vbr->flags = 0;
    if (bio->bi_rw & REQ_FLUSH)
        vbr->flags |= VBLK_REQ_FLUSH;
    if (bio->bi_rw & REQ_FUA)
        vbr->flags |= VBLK_REQ_FUA;
    if (bio->bi_size)
        vbr->flags |= VBLK_REQ_DATA;

    if (unlikely(vbr->flags & VBLK_REQ_FLUSH))
        virtblk_bio_send_flush(vbr);
    else
        virtblk_bio_send_data(vbr);
}

/* return id (s/n) string for *disk to *id_str
 */
static int virtblk_get_id(struct gendisk *disk, char *id_str)
{
    struct virtio_blk *vblk = disk->private_data;
    struct request *req;
    struct bio *bio;
    int err;

    bio = bio_map_kern(vblk->disk->queue, id_str, VIRTIO_BLK_ID_BYTES,
               GFP_KERNEL);
    if (IS_ERR(bio))
        return PTR_ERR(bio);

    req = blk_make_request(vblk->disk->queue, bio, GFP_KERNEL);
    if (IS_ERR(req)) {
        bio_put(bio);
        return PTR_ERR(req);
    }

    req->cmd_type = REQ_TYPE_SPECIAL;
    err = blk_execute_rq(vblk->disk->queue, vblk->disk, req, false);
    blk_put_request(req);

    return err;
}

static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
                 unsigned int cmd, unsigned long data)
{
    struct gendisk *disk = bdev->bd_disk;
    struct virtio_blk *vblk = disk->private_data;

    /*
     * Only allow the generic SCSI ioctls if the host can support it.
     */
    if (!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_SCSI))
        return -ENOTTY;

    return scsi_cmd_blk_ioctl(bdev, mode, cmd,
                  (void __user *)data);
}

/* We provide getgeo only to please some old bootloader/partitioning tools */
static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
{
    struct virtio_blk *vblk = bd->bd_disk->private_data;
    struct virtio_blk_geometry vgeo;
    int err;

    /* see if the host passed in geometry config */
    err = virtio_config_val(vblk->vdev, VIRTIO_BLK_F_GEOMETRY,
                offsetof(struct virtio_blk_config, geometry),
                &vgeo);

    if (!err) {
        geo->heads = vgeo.heads;
        geo->sectors = vgeo.sectors;
        geo->cylinders = vgeo.cylinders;
    } else {
        /* some standard values, similar to sd */
        geo->heads = 1 << 6;
        geo->sectors = 1 << 5;
        geo->cylinders = get_capacity(bd->bd_disk) >> 11;
    }
    return 0;
}

static const struct block_device_operations virtblk_fops = {
    .ioctl  = virtblk_ioctl,
    .owner  = THIS_MODULE,
    .getgeo = virtblk_getgeo,
};

static int index_to_minor(int index)
{
    return index << PART_BITS;
}

static int minor_to_index(int minor)
{
    return minor >> PART_BITS;
}

static ssize_t virtblk_serial_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    struct gendisk *disk = dev_to_disk(dev);
    int err;

    /* sysfs gives us a PAGE_SIZE buffer */
    BUILD_BUG_ON(PAGE_SIZE < VIRTIO_BLK_ID_BYTES);

    buf[VIRTIO_BLK_ID_BYTES] = '\0';
    err = virtblk_get_id(disk, buf);
    if (!err)
        return strlen(buf);

    if (err == -EIO) /* Unsupported? Make it empty. */
        return 0;

    return err;
}
DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);

static void virtblk_config_changed_work(struct work_struct *work)
{
    struct virtio_blk *vblk =
        container_of(work, struct virtio_blk, config_work);
    struct virtio_device *vdev = vblk->vdev;
    struct request_queue *q = vblk->disk->queue;
    char cap_str_2[10], cap_str_10[10];
    u64 capacity, size;

    mutex_lock(&vblk->config_lock);
    if (!vblk->config_enable)
        goto done;

    /* Host must always specify the capacity. */
    vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
              &capacity, sizeof(capacity));

    /* If capacity is too big, truncate with warning. */
    if ((sector_t)capacity != capacity) {
        dev_warn(&vdev->dev, "Capacity %llu too large: truncating\n",
             (unsigned long long)capacity);
        capacity = (sector_t)-1;
    }

    size = capacity * queue_logical_block_size(q);
    string_get_size(size, STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
    string_get_size(size, STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));

    dev_notice(&vdev->dev,
          "new size: %llu %d-byte logical blocks (%s/%s)\n",
          (unsigned long long)capacity,
          queue_logical_block_size(q),
          cap_str_10, cap_str_2);

    set_capacity(vblk->disk, capacity);
    revalidate_disk(vblk->disk);
done:
    mutex_unlock(&vblk->config_lock);
}

static void virtblk_config_changed(struct virtio_device *vdev)
{
    struct virtio_blk *vblk = vdev->priv;

    queue_work(virtblk_wq, &vblk->config_work);
}

static int init_vq(struct virtio_blk *vblk)
{
    int err = 0;

    /* We expect one virtqueue, for output. */
    vblk->vq = virtio_find_single_vq(vblk->vdev, virtblk_done, "requests");
    if (IS_ERR(vblk->vq))
        err = PTR_ERR(vblk->vq);

    return err;
}

/*
 * Legacy naming scheme used for virtio devices.  We are stuck with it for
 * virtio blk but don't ever use it for any new driver.
 */
static int virtblk_name_format(char *prefix, int index, char *buf, int buflen)
{
    const int base = 'z' - 'a' + 1;
    char *begin = buf + strlen(prefix);
    char *end = buf + buflen;
    char *p;
    int unit;

    p = end - 1;
    *p = '\0';
    unit = base;
    do {
        if (p == begin)
            return -EINVAL;
        *--p = 'a' + (index % unit);
        index = (index / unit) - 1;
    } while (index >= 0);

    memmove(begin, p, end - p);
    memcpy(buf, prefix, strlen(prefix));

    return 0;
}

static int virtblk_get_cache_mode(struct virtio_device *vdev)
{
    u8 writeback;
    int err;

    err = virtio_config_val(vdev, VIRTIO_BLK_F_CONFIG_WCE,
                offsetof(struct virtio_blk_config, wce),
                &writeback);
    if (err)
        writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_WCE);

    return writeback;
}

static void virtblk_update_cache_mode(struct virtio_device *vdev)
{
    u8 writeback = virtblk_get_cache_mode(vdev);
    struct virtio_blk *vblk = vdev->priv;

    if (writeback)
        blk_queue_flush(vblk->disk->queue, REQ_FLUSH);
    else
        blk_queue_flush(vblk->disk->queue, 0);

    revalidate_disk(vblk->disk);
}

static const char *const virtblk_cache_types[] = {
    "write through", "write back"
};

static ssize_t
virtblk_cache_type_store(struct device *dev, struct device_attribute *attr,
             const char *buf, size_t count)
{
    struct gendisk *disk = dev_to_disk(dev);
    struct virtio_blk *vblk = disk->private_data;
    struct virtio_device *vdev = vblk->vdev;
    int i;
    u8 writeback;

    BUG_ON(!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_CONFIG_WCE));
    for (i = ARRAY_SIZE(virtblk_cache_types); --i >= 0; )
        if (sysfs_streq(buf, virtblk_cache_types[i]))
            break;

    if (i < 0)
        return -EINVAL;

    writeback = i;
    vdev->config->set(vdev,
              offsetof(struct virtio_blk_config, wce),
              &writeback, sizeof(writeback));

    virtblk_update_cache_mode(vdev);
    return count;
}

static ssize_t
virtblk_cache_type_show(struct device *dev, struct device_attribute *attr,
             char *buf)
{
    struct gendisk *disk = dev_to_disk(dev);
    struct virtio_blk *vblk = disk->private_data;
    u8 writeback = virtblk_get_cache_mode(vblk->vdev);

    BUG_ON(writeback >= ARRAY_SIZE(virtblk_cache_types));
    return snprintf(buf, 40, "%s\n", virtblk_cache_types[writeback]);
}

static const struct device_attribute dev_attr_cache_type_ro =
    __ATTR(cache_type, S_IRUGO,
           virtblk_cache_type_show, NULL);
static const struct device_attribute dev_attr_cache_type_rw =
    __ATTR(cache_type, S_IRUGO|S_IWUSR,
           virtblk_cache_type_show, virtblk_cache_type_store);

static int __devinit virtblk_probe(struct virtio_device *vdev)
{
    struct virtio_blk *vblk;
    struct request_queue *q;
    int err, index;
    int pool_size;

    u64 cap;
    u32 v, blk_size, sg_elems, opt_io_size;
    u16 min_io_size;
    u8 physical_block_exp, alignment_offset;

    err = ida_simple_get(&vd_index_ida, 0, minor_to_index(1 << MINORBITS),
                 GFP_KERNEL);
    if (err < 0)
        goto out;
    index = err;

    /* We need to know how many segments before we allocate. */
    err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
                offsetof(struct virtio_blk_config, seg_max),
                &sg_elems);

    /* We need at least one SG element, whatever they say. */
    if (err || !sg_elems)
        sg_elems = 1;

    /* We need an extra sg elements at head and tail. */
    sg_elems += 2;
    vdev->priv = vblk = kmalloc(sizeof(*vblk) +
                    sizeof(vblk->sg[0]) * sg_elems, GFP_KERNEL);
    if (!vblk) {
        err = -ENOMEM;
        goto out_free_index;
    }

    init_waitqueue_head(&vblk->queue_wait);
    vblk->vdev = vdev;
    vblk->sg_elems = sg_elems;
    sg_init_table(vblk->sg, vblk->sg_elems);
    mutex_init(&vblk->config_lock);

    INIT_WORK(&vblk->config_work, virtblk_config_changed_work);
    vblk->config_enable = true;

    err = init_vq(vblk);
    if (err)
        goto out_free_vblk;

    pool_size = sizeof(struct virtblk_req);
    if (use_bio)
        pool_size += sizeof(struct scatterlist) * sg_elems;
    vblk->pool = mempool_create_kmalloc_pool(1, pool_size);
    if (!vblk->pool) {
        err = -ENOMEM;
        goto out_free_vq;
    }

    /* FIXME: How many partitions?  How long is a piece of string? */
    vblk->disk = alloc_disk(1 << PART_BITS);
    if (!vblk->disk) {
        err = -ENOMEM;
        goto out_mempool;
    }

    q = vblk->disk->queue = blk_init_queue(virtblk_request, NULL);
    if (!q) {
        err = -ENOMEM;
        goto out_put_disk;
    }

    if (use_bio)
        blk_queue_make_request(q, virtblk_make_request);
    q->queuedata = vblk;

    virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN);

    vblk->disk->major = major;
    vblk->disk->first_minor = index_to_minor(index);
    vblk->disk->private_data = vblk;
    vblk->disk->fops = &virtblk_fops;
    vblk->disk->driverfs_dev = &vdev->dev;
    vblk->index = index;

    /* configure queue flush support */
    virtblk_update_cache_mode(vdev);

    /* If disk is read-only in the host, the guest should obey */
    if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
        set_disk_ro(vblk->disk, 1);

    /* Host must always specify the capacity. */
    vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
              &cap, sizeof(cap));

    /* If capacity is too big, truncate with warning. */
    if ((sector_t)cap != cap) {
        dev_warn(&vdev->dev, "Capacity %llu too large: truncating\n",
             (unsigned long long)cap);
        cap = (sector_t)-1;
    }
    set_capacity(vblk->disk, cap);

    /* We can handle whatever the host told us to handle. */
    blk_queue_max_segments(q, vblk->sg_elems-2);

    /* No need to bounce any requests */
    blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);

    /* No real sector limit. */
    blk_queue_max_hw_sectors(q, -1U);

    /* Host can optionally specify maximum segment size and number of
     * segments. */
    err = virtio_config_val(vdev, VIRTIO_BLK_F_SIZE_MAX,
                offsetof(struct virtio_blk_config, size_max),
                &v);
    if (!err)
        blk_queue_max_segment_size(q, v);
    else
        blk_queue_max_segment_size(q, -1U);

    /* Host can optionally specify the block size of the device */
    err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
                offsetof(struct virtio_blk_config, blk_size),
                &blk_size);
    if (!err)
        blk_queue_logical_block_size(q, blk_size);
    else
        blk_size = queue_logical_block_size(q);

    /* Use topology information if available */
    err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
            offsetof(struct virtio_blk_config, physical_block_exp),
            &physical_block_exp);
    if (!err && physical_block_exp)
        blk_queue_physical_block_size(q,
                blk_size * (1 << physical_block_exp));

    err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
            offsetof(struct virtio_blk_config, alignment_offset),
            &alignment_offset);
    if (!err && alignment_offset)
        blk_queue_alignment_offset(q, blk_size * alignment_offset);

    err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
            offsetof(struct virtio_blk_config, min_io_size),
            &min_io_size);
    if (!err && min_io_size)
        blk_queue_io_min(q, blk_size * min_io_size);

    err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
            offsetof(struct virtio_blk_config, opt_io_size),
            &opt_io_size);
    if (!err && opt_io_size)
        blk_queue_io_opt(q, blk_size * opt_io_size);

    add_disk(vblk->disk);
    err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial);
    if (err)
        goto out_del_disk;

    if (virtio_has_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE))
        err = device_create_file(disk_to_dev(vblk->disk),
                     &dev_attr_cache_type_rw);
    else
        err = device_create_file(disk_to_dev(vblk->disk),
                     &dev_attr_cache_type_ro);
    if (err)
        goto out_del_disk;
    return 0;

out_del_disk:
    del_gendisk(vblk->disk);
    blk_cleanup_queue(vblk->disk->queue);
out_put_disk:
    put_disk(vblk->disk);
out_mempool:
    mempool_destroy(vblk->pool);
out_free_vq:
    vdev->config->del_vqs(vdev);
out_free_vblk:
    kfree(vblk);
out_free_index:
    ida_simple_remove(&vd_index_ida, index);
out:
    return err;
}

static void __devexit virtblk_remove(struct virtio_device *vdev)
{
    struct virtio_blk *vblk = vdev->priv;
    int index = vblk->index;

    /* Prevent config work handler from accessing the device. */
    mutex_lock(&vblk->config_lock);
    vblk->config_enable = false;
    mutex_unlock(&vblk->config_lock);

    del_gendisk(vblk->disk);
    blk_cleanup_queue(vblk->disk->queue);

    /* Stop all the virtqueues. */
    vdev->config->reset(vdev);

    flush_work(&vblk->config_work);

    put_disk(vblk->disk);
    mempool_destroy(vblk->pool);
    vdev->config->del_vqs(vdev);
    kfree(vblk);
    ida_simple_remove(&vd_index_ida, index);
}

#ifdef CONFIG_PM
static int virtblk_freeze(struct virtio_device *vdev)
{
    struct virtio_blk *vblk = vdev->priv;

    /* Ensure we don't receive any more interrupts */
    vdev->config->reset(vdev);

    /* Prevent config work handler from accessing the device. */
    mutex_lock(&vblk->config_lock);
    vblk->config_enable = false;
    mutex_unlock(&vblk->config_lock);

    flush_work(&vblk->config_work);

    spin_lock_irq(vblk->disk->queue->queue_lock);
    blk_stop_queue(vblk->disk->queue);
    spin_unlock_irq(vblk->disk->queue->queue_lock);
    blk_sync_queue(vblk->disk->queue);

    vdev->config->del_vqs(vdev);
    return 0;
}

static int virtblk_restore(struct virtio_device *vdev)
{
    struct virtio_blk *vblk = vdev->priv;
    int ret;

    vblk->config_enable = true;
    ret = init_vq(vdev->priv);
    if (!ret) {
        spin_lock_irq(vblk->disk->queue->queue_lock);
        blk_start_queue(vblk->disk->queue);
        spin_unlock_irq(vblk->disk->queue->queue_lock);
    }
    return ret;
}
#endif

static const struct virtio_device_id id_table[] = {
    { VIRTIO_ID_BLOCK, VIRTIO_DEV_ANY_ID },
    { 0 },
};

static unsigned int features[] = {
    VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
    VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE, VIRTIO_BLK_F_SCSI,
    VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE
};

/*
 * virtio_blk causes spurious section mismatch warning by
 * simultaneously referring to a __devinit and a __devexit function.
 * Use __refdata to avoid this warning.
 */
static struct virtio_driver __refdata virtio_blk = {
    .feature_table      = features,
    .feature_table_size = ARRAY_SIZE(features),
    .driver.name        = KBUILD_MODNAME,
    .driver.owner       = THIS_MODULE,
    .id_table       = id_table,
    .probe          = virtblk_probe,
    .remove         = __devexit_p(virtblk_remove),
    .config_changed     = virtblk_config_changed,
#ifdef CONFIG_PM
    .freeze         = virtblk_freeze,
    .restore        = virtblk_restore,
#endif
};

static int __init init(void)
{
    int error;

    virtblk_wq = alloc_workqueue("virtio-blk", 0, 0);
    if (!virtblk_wq)
        return -ENOMEM;

    major = register_blkdev(0, "virtblk");
    if (major < 0) {
        error = major;
        goto out_destroy_workqueue;
    }

    error = register_virtio_driver(&virtio_blk);
    if (error)
        goto out_unregister_blkdev;
    return 0;

out_unregister_blkdev:
    unregister_blkdev(major, "virtblk");
out_destroy_workqueue:
    destroy_workqueue(virtblk_wq);
    return error;
}

static void __exit fini(void)
{
    unregister_blkdev(major, "virtblk");
    unregister_virtio_driver(&virtio_blk);
    destroy_workqueue(virtblk_wq);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio block driver");
MODULE_LICENSE("GPL");