//#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 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 virtblk_remove(struct virtio_device *vdev)
{
        struct virtio_blk *vblk = vdev->priv;
        int index = vblk->index;
        int refc;

        /* 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);

        refc = atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount);
        put_disk(vblk->disk);
        mempool_destroy(vblk->pool);
        vdev->config->del_vqs(vdev);
        kfree(vblk);

        /* Only free device id if we don't have any users */
        if (refc == 1)
                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
};

static struct virtio_driver 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                 = 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");