drivers/block/virtio_blk.c - third_party/linux - Git at Google

 //#define DEBUG
 #include <linux/spinlock.h>
 #include <linux/blkdev.h>
 #include <linux/hdreg.h>
 #include <linux/virtio.h>
 #include <linux/virtio_blk.h>
 #include <linux/scatterlist.h>

 #define PART_BITS 4

 static int major, index;

 struct virtio_blk
 {
 	spinlock_t lock;

 	struct virtio_device *vdev;
 	struct virtqueue *vq;

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

 	/* Request tracking. */
 	struct list_head reqs;

 	mempool_t *pool;

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

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

 struct virtblk_req
 {
 	struct list_head list;
 	struct request *req;
 	struct virtio_blk_outhdr out_hdr;
 	struct virtio_scsi_inhdr in_hdr;
 	u8 status;
 };

 static void blk_done(struct virtqueue *vq)
 {
 	struct virtio_blk *vblk = vq->vdev->priv;
 	struct virtblk_req *vbr;
 	unsigned int len;
 	unsigned long flags;

 	spin_lock_irqsave(&vblk->lock, flags);
 	while ((vbr = vblk->vq->vq_ops->get_buf(vblk->vq, &len)) != NULL) {
 		int error;

 		switch (vbr->status) {
 		case VIRTIO_BLK_S_OK:
 			error = 0;
 			break;
 		case VIRTIO_BLK_S_UNSUPP:
 			error = -ENOTTY;
 			break;
 		default:
 			error = -EIO;
 			break;
 		}

 		if (blk_pc_request(vbr->req)) {
 			vbr->req->resid_len = vbr->in_hdr.residual;
 			vbr->req->sense_len = vbr->in_hdr.sense_len;
 			vbr->req->errors = vbr->in_hdr.errors;
 		}

 		__blk_end_request_all(vbr->req, error);
 		list_del(&vbr->list);
 		mempool_free(vbr, vblk->pool);
 	}
 	/* In case queue is stopped waiting for more buffers. */
 	blk_start_queue(vblk->disk->queue);
 	spin_unlock_irqrestore(&vblk->lock, flags);
 }

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

 	vbr->req = req;
 	if (blk_fs_request(vbr->req)) {
 		vbr->out_hdr.type = 0;
 		vbr->out_hdr.sector = blk_rq_pos(vbr->req);
 		vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
 	} else if (blk_pc_request(vbr->req)) {
 		vbr->out_hdr.type = VIRTIO_BLK_T_SCSI_CMD;
 		vbr->out_hdr.sector = 0;
 		vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
 	} else {
 		/* We don't put anything else in the queue. */
 		BUG();
 	}

 	if (blk_barrier_rq(vbr->req))
 		vbr->out_hdr.type |= VIRTIO_BLK_T_BARRIER;

 	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 (blk_pc_request(vbr->req))
 		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 (blk_pc_request(vbr->req)) {
 		sg_set_buf(&vblk->sg[num + out + in++], vbr->req->sense, 96);
 		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 (vblk->vq->vq_ops->add_buf(vblk->vq, vblk->sg, out, in, vbr)) {
 		mempool_free(vbr, vblk->pool);
 		return false;
 	}

 	list_add_tail(&vbr->list, &vblk->reqs);
 	return true;
 }

 static void do_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)
 		vblk->vq->vq_ops->kick(vblk->vq);
 }

 /* return ATA identify data
  */
 static int virtblk_identify(struct gendisk *disk, void *argp)
 {
 	struct virtio_blk *vblk = disk->private_data;
 	void *opaque;
 	int err = -ENOMEM;

 	opaque = kmalloc(VIRTIO_BLK_ID_BYTES, GFP_KERNEL);
 	if (!opaque)
 		goto out;

 	err = virtio_config_buf(vblk->vdev, VIRTIO_BLK_F_IDENTIFY,
 		offsetof(struct virtio_blk_config, identify), opaque,
 		VIRTIO_BLK_ID_BYTES);

 	if (err)
 		goto out_kfree;

 	if (copy_to_user(argp, opaque, VIRTIO_BLK_ID_BYTES))
 		err = -EFAULT;

 out_kfree:
 	kfree(opaque);
 out:
 	return err;
 }

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

 	if (cmd == HDIO_GET_IDENTITY)
 		return virtblk_identify(disk, argp);

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

 	return scsi_cmd_ioctl(disk->queue, disk, mode, cmd, argp);
 }

 /* 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 struct block_device_operations virtblk_fops = {
 	.locked_ioctl = virtblk_ioctl,
 	.owner  = THIS_MODULE,
 	.getgeo = virtblk_getgeo,
 };

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

 static int __devinit virtblk_probe(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk;
 	int err;
 	u64 cap;
 	u32 v;
 	u32 blk_size, sg_elems;

 	if (index_to_minor(index) >= 1 << MINORBITS)
 		return -ENOSPC;

 	/* 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);
 	if (err)
 		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;
 	}

 	INIT_LIST_HEAD(&vblk->reqs);
 	spin_lock_init(&vblk->lock);
 	vblk->vdev = vdev;
 	vblk->sg_elems = sg_elems;
 	sg_init_table(vblk->sg, vblk->sg_elems);

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

 	vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
 	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;
 	}

 	vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
 	if (!vblk->disk->queue) {
 		err = -ENOMEM;
 		goto out_put_disk;
 	}

 	vblk->disk->queue->queuedata = vblk;
 	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, vblk->disk->queue);

 	if (index < 26) {
 		sprintf(vblk->disk->disk_name, "vd%c", 'a' + index % 26);
 	} else if (index < (26 + 1) * 26) {
 		sprintf(vblk->disk->disk_name, "vd%c%c",
 			'a' + index / 26 - 1, 'a' + index % 26);
 	} else {
 		const unsigned int m1 = (index / 26 - 1) / 26 - 1;
 		const unsigned int m2 = (index / 26 - 1) % 26;
 		const unsigned int m3 =  index % 26;
 		sprintf(vblk->disk->disk_name, "vd%c%c%c",
 			'a' + m1, 'a' + m2, 'a' + m3);
 	}

 	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;
 	index++;

 	/* If barriers are supported, tell block layer that queue is ordered */
 	if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
 		blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);

 	/* 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_phys_segments(vblk->disk->queue, vblk->sg_elems-2);
 	blk_queue_max_hw_segments(vblk->disk->queue, vblk->sg_elems-2);

 	/* No real sector limit. */
 	blk_queue_max_sectors(vblk->disk->queue, -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(vblk->disk->queue, v);
 	else
 		blk_queue_max_segment_size(vblk->disk->queue, -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(vblk->disk->queue, blk_size);

 	add_disk(vblk->disk);
 	return 0;

 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:
 	return err;
 }

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

 	/* Nothing should be pending. */
 	BUG_ON(!list_empty(&vblk->reqs));

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

 	del_gendisk(vblk->disk);
 	blk_cleanup_queue(vblk->disk->queue);
 	put_disk(vblk->disk);
 	mempool_destroy(vblk->pool);
 	vdev->config->del_vqs(vdev);
 	kfree(vblk);
 }

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

 static unsigned int features[] = {
 	VIRTIO_BLK_F_BARRIER, 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_IDENTIFY
 };

 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 =	__devexit_p(virtblk_remove),
 };

 static int __init init(void)
 {
 	major = register_blkdev(0, "virtblk");
 	if (major < 0)
 		return major;
 	return register_virtio_driver(&virtio_blk);
 }

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

 MODULE_DEVICE_TABLE(virtio, id_table);
 MODULE_DESCRIPTION("Virtio block driver");
 MODULE_LICENSE("GPL");
	//#define DEBUG
	#include <linux/spinlock.h>
	#include <linux/blkdev.h>
	#include <linux/hdreg.h>
	#include <linux/virtio.h>
	#include <linux/virtio_blk.h>
	#include <linux/scatterlist.h>

	#define PART_BITS 4

	static int major, index;

	struct virtio_blk
	{
	spinlock_t lock;

	struct virtio_device *vdev;
	struct virtqueue *vq;

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

	/* Request tracking. */
	struct list_head reqs;

	mempool_t *pool;

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

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

	struct virtblk_req
	{
	struct list_head list;
	struct request *req;
	struct virtio_blk_outhdr out_hdr;
	struct virtio_scsi_inhdr in_hdr;
	u8 status;
	};

	static void blk_done(struct virtqueue *vq)
	{
	struct virtio_blk *vblk = vq->vdev->priv;
	struct virtblk_req *vbr;
	unsigned int len;
	unsigned long flags;

	spin_lock_irqsave(&vblk->lock, flags);
	while ((vbr = vblk->vq->vq_ops->get_buf(vblk->vq, &len)) != NULL) {
	int error;

	switch (vbr->status) {
	case VIRTIO_BLK_S_OK:
	error = 0;
	break;
	case VIRTIO_BLK_S_UNSUPP:
	error = -ENOTTY;
	break;
	default:
	error = -EIO;
	break;
	}

	if (blk_pc_request(vbr->req)) {
	vbr->req->resid_len = vbr->in_hdr.residual;
	vbr->req->sense_len = vbr->in_hdr.sense_len;
	vbr->req->errors = vbr->in_hdr.errors;
	}

	__blk_end_request_all(vbr->req, error);
	list_del(&vbr->list);
	mempool_free(vbr, vblk->pool);
	}
	/* In case queue is stopped waiting for more buffers. */
	blk_start_queue(vblk->disk->queue);
	spin_unlock_irqrestore(&vblk->lock, flags);
	}

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

	vbr->req = req;
	if (blk_fs_request(vbr->req)) {
	vbr->out_hdr.type = 0;
	vbr->out_hdr.sector = blk_rq_pos(vbr->req);
	vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
	} else if (blk_pc_request(vbr->req)) {
	vbr->out_hdr.type = VIRTIO_BLK_T_SCSI_CMD;
	vbr->out_hdr.sector = 0;
	vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
	} else {
	/* We don't put anything else in the queue. */
	BUG();
	}

	if (blk_barrier_rq(vbr->req))
	vbr->out_hdr.type \|= VIRTIO_BLK_T_BARRIER;

	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 (blk_pc_request(vbr->req))
	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 (blk_pc_request(vbr->req)) {
	sg_set_buf(&vblk->sg[num + out + in++], vbr->req->sense, 96);
	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 (vblk->vq->vq_ops->add_buf(vblk->vq, vblk->sg, out, in, vbr)) {
	mempool_free(vbr, vblk->pool);
	return false;
	}

	list_add_tail(&vbr->list, &vblk->reqs);
	return true;
	}

	static void do_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)
	vblk->vq->vq_ops->kick(vblk->vq);
	}

	/* return ATA identify data
	*/
	static int virtblk_identify(struct gendisk disk, void argp)
	{
	struct virtio_blk *vblk = disk->private_data;
	void *opaque;
	int err = -ENOMEM;

	opaque = kmalloc(VIRTIO_BLK_ID_BYTES, GFP_KERNEL);
	if (!opaque)
	goto out;

	err = virtio_config_buf(vblk->vdev, VIRTIO_BLK_F_IDENTIFY,
	offsetof(struct virtio_blk_config, identify), opaque,
	VIRTIO_BLK_ID_BYTES);

	if (err)
	goto out_kfree;

	if (copy_to_user(argp, opaque, VIRTIO_BLK_ID_BYTES))
	err = -EFAULT;

	out_kfree:
	kfree(opaque);
	out:
	return err;
	}

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

	if (cmd == HDIO_GET_IDENTITY)
	return virtblk_identify(disk, argp);

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

	return scsi_cmd_ioctl(disk->queue, disk, mode, cmd, argp);
	}

	/* 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 struct block_device_operations virtblk_fops = {
	.locked_ioctl = virtblk_ioctl,
	.owner = THIS_MODULE,
	.getgeo = virtblk_getgeo,
	};

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

	static int __devinit virtblk_probe(struct virtio_device *vdev)
	{
	struct virtio_blk *vblk;
	int err;
	u64 cap;
	u32 v;
	u32 blk_size, sg_elems;

	if (index_to_minor(index) >= 1 << MINORBITS)
	return -ENOSPC;

	/* 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);
	if (err)
	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;
	}

	INIT_LIST_HEAD(&vblk->reqs);
	spin_lock_init(&vblk->lock);
	vblk->vdev = vdev;
	vblk->sg_elems = sg_elems;
	sg_init_table(vblk->sg, vblk->sg_elems);

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

	vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
	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;
	}

	vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
	if (!vblk->disk->queue) {
	err = -ENOMEM;
	goto out_put_disk;
	}

	vblk->disk->queue->queuedata = vblk;
	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, vblk->disk->queue);

	if (index < 26) {
	sprintf(vblk->disk->disk_name, "vd%c", 'a' + index % 26);
	} else if (index < (26 + 1) * 26) {
	sprintf(vblk->disk->disk_name, "vd%c%c",
	'a' + index / 26 - 1, 'a' + index % 26);
	} else {
	const unsigned int m1 = (index / 26 - 1) / 26 - 1;
	const unsigned int m2 = (index / 26 - 1) % 26;
	const unsigned int m3 = index % 26;
	sprintf(vblk->disk->disk_name, "vd%c%c%c",
	'a' + m1, 'a' + m2, 'a' + m3);
	}

	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;
	index++;

	/* If barriers are supported, tell block layer that queue is ordered */
	if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
	blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);

	/* 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_phys_segments(vblk->disk->queue, vblk->sg_elems-2);
	blk_queue_max_hw_segments(vblk->disk->queue, vblk->sg_elems-2);

	/* No real sector limit. */
	blk_queue_max_sectors(vblk->disk->queue, -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(vblk->disk->queue, v);
	else
	blk_queue_max_segment_size(vblk->disk->queue, -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(vblk->disk->queue, blk_size);

	add_disk(vblk->disk);
	return 0;

	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:
	return err;
	}

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

	/* Nothing should be pending. */
	BUG_ON(!list_empty(&vblk->reqs));

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

	del_gendisk(vblk->disk);
	blk_cleanup_queue(vblk->disk->queue);
	put_disk(vblk->disk);
	mempool_destroy(vblk->pool);
	vdev->config->del_vqs(vdev);
	kfree(vblk);
	}

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

	static unsigned int features[] = {
	VIRTIO_BLK_F_BARRIER, 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_IDENTIFY
	};

	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 = __devexit_p(virtblk_remove),
	};

	static int __init init(void)
	{
	major = register_blkdev(0, "virtblk");
	if (major < 0)
	return major;
	return register_virtio_driver(&virtio_blk);
	}

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

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