Block driver using virtio.

The block driver uses scatter-gather lists with sg[0] being the
request information (struct virtio_blk_outhdr) with the type, sector
and inbuf id.  The next N sg entries are the bio itself, then the last
sg is the status byte.  Whether the N entries are in or out depends on
whether it's a read or a write.

We accept the normal (SCSI) ioctls: they get handed through to the other
side which can then handle it or reply that it's unsupported.  It's
not clear that this actually works in general, since I don't know
if blk_pc_request() requests have an accurate rq_data_dir().

Although we try to reply -ENOTTY on unsupported commands, ioctl(fd,
CDROMEJECT) returns success to userspace.  This needs a separate
patch.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <jens.axboe@oracle.com>

5 files changed, 367 insertions, 0 deletions

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index ce4b1e484e64..4d0119ea9e35 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -425,4 +425,10 @@ config XEN_BLKDEV_FRONTEND
           block device driver.  It communicates with a back-end driver
           in another domain which drives the actual block device.
 
+config VIRTIO_BLK
+        tristate "Virtio block driver (EXPERIMENTAL)"
+        depends on EXPERIMENTAL && VIRTIO
+        ---help---
+          This is the virtual block driver for lguest.  Say Y or M.
+
 endif # BLK_DEV
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index 014e72121b5a..d199eba7a080 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_SUNVDC)		+= sunvdc.o
 obj-$(CONFIG_BLK_DEV_UMEM)      += umem.o
 obj-$(CONFIG_BLK_DEV_NBD)       += nbd.o
 obj-$(CONFIG_BLK_DEV_CRYPTOLOOP) += cryptoloop.o
+obj-$(CONFIG_VIRTIO_BLK)        += virtio_blk.o
 
 obj-$(CONFIG_VIODASD)           += viodasd.o
 obj-$(CONFIG_BLK_DEV_SX8)       += sx8.o
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
new file mode 100644
index 000000000000..a901eee64ba5
--- /dev/null
+++ b/drivers/block/virtio_blk.c
@@ -0,0 +1,308 @@
+//#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/virtio_blk.h>
+
+static unsigned char virtblk_index = 'a';
+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;
+
+        /* Scatterlist: can be too big for stack. */
+        struct scatterlist sg[3+MAX_PHYS_SEGMENTS];
+};
+
+struct virtblk_req
+{
+        struct list_head list;
+        struct request *req;
+        struct virtio_blk_outhdr out_hdr;
+        struct virtio_blk_inhdr in_hdr;
+};
+
+static bool 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 uptodate;
+                switch (vbr->in_hdr.status) {
+                case VIRTIO_BLK_S_OK:
+                        uptodate = 1;
+                        break;
+                case VIRTIO_BLK_S_UNSUPP:
+                        uptodate = -ENOTTY;
+                        break;
+                default:
+                        uptodate = 0;
+                        break;
+                }
+
+                end_dequeued_request(vbr->req, uptodate);
+                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);
+        return true;
+}
+
+static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
+                   struct request *req)
+{
+        unsigned long num, out, in;
+        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 = vbr->req->sector;
+                vbr->out_hdr.ioprio = vbr->req->ioprio;
+        } 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 = vbr->req->ioprio;
+        } 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;
+
+        /* We have to zero this, otherwise blk_rq_map_sg gets upset. */
+        memset(vblk->sg, 0, sizeof(vblk->sg));
+        sg_set_buf(&vblk->sg[0], &vbr->out_hdr, sizeof(vbr->out_hdr));
+        num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
+        sg_set_buf(&vblk->sg[num+1], &vbr->in_hdr, sizeof(vbr->in_hdr));
+
+        if (rq_data_dir(vbr->req) == WRITE) {
+                vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
+                out = 1 + num;
+                in = 1;
+        } else {
+                vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
+                out = 1;
+                in = 1 + 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 = NULL;
+        struct request *req;
+        unsigned int issued = 0;
+
+        while ((req = elv_next_request(q)) != NULL) {
+                vblk = req->rq_disk->private_data;
+                BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg));
+
+                /* 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;
+                }
+                blkdev_dequeue_request(req);
+                issued++;
+        }
+
+        if (issued)
+                vblk->vq->vq_ops->kick(vblk->vq);
+}
+
+static int virtblk_ioctl(struct inode *inode, struct file *filp,
+                         unsigned cmd, unsigned long data)
+{
+        return scsi_cmd_ioctl(filp, inode->i_bdev->bd_disk->queue,
+                              inode->i_bdev->bd_disk, cmd,
+                              (void __user *)data);
+}
+
+static struct block_device_operations virtblk_fops = {
+        .ioctl = virtblk_ioctl,
+        .owner = THIS_MODULE,
+};
+
+static int virtblk_probe(struct virtio_device *vdev)
+{
+        struct virtio_blk *vblk;
+        int err, major;
+        void *token;
+        unsigned int len;
+        u64 cap;
+        u32 v;
+
+        vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+        if (!vblk) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+        INIT_LIST_HEAD(&vblk->reqs);
+        spin_lock_init(&vblk->lock);
+        vblk->vdev = vdev;
+
+        /* We expect one virtqueue, for output. */
+        vblk->vq = vdev->config->find_vq(vdev, blk_done);
+        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;
+        }
+
+        major = register_blkdev(0, "virtblk");
+        if (major < 0) {
+                err = major;
+                goto out_mempool;
+        }
+
+        /* FIXME: How many partitions?  How long is a piece of string? */
+        vblk->disk = alloc_disk(1 << 4);
+        if (!vblk->disk) {
+                err = -ENOMEM;
+                goto out_unregister_blkdev;
+        }
+
+        vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
+        if (!vblk->disk->queue) {
+                err = -ENOMEM;
+                goto out_put_disk;
+        }
+
+        sprintf(vblk->disk->disk_name, "vd%c", virtblk_index++);
+        vblk->disk->major = major;
+        vblk->disk->first_minor = 0;
+        vblk->disk->private_data = vblk;
+        vblk->disk->fops = &virtblk_fops;
+
+        /* If barriers are supported, tell block layer that queue is ordered */
+        token = vdev->config->find(vdev, VIRTIO_CONFIG_BLK_F, &len);
+        if (virtio_use_bit(vdev, token, len, VIRTIO_BLK_F_BARRIER))
+                blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);
+
+        err = virtio_config_val(vdev, VIRTIO_CONFIG_BLK_F_CAPACITY, &cap);
+        if (err) {
+                dev_err(&vdev->dev, "Bad/missing capacity in config\n");
+                goto out_put_disk;
+        }
+
+        /* 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);
+
+        err = virtio_config_val(vdev, VIRTIO_CONFIG_BLK_F_SIZE_MAX, &v);
+        if (!err)
+                blk_queue_max_segment_size(vblk->disk->queue, v);
+        else if (err != -ENOENT) {
+                dev_err(&vdev->dev, "Bad SIZE_MAX in config\n");
+                goto out_put_disk;
+        }
+
+        err = virtio_config_val(vdev, VIRTIO_CONFIG_BLK_F_SEG_MAX, &v);
+        if (!err)
+                blk_queue_max_hw_segments(vblk->disk->queue, v);
+        else if (err != -ENOENT) {
+                dev_err(&vdev->dev, "Bad SEG_MAX in config\n");
+                goto out_put_disk;
+        }
+
+        add_disk(vblk->disk);
+        return 0;
+
+out_put_disk:
+        put_disk(vblk->disk);
+out_unregister_blkdev:
+        unregister_blkdev(major, "virtblk");
+out_mempool:
+        mempool_destroy(vblk->pool);
+out_free_vq:
+        vdev->config->del_vq(vblk->vq);
+out_free_vblk:
+        kfree(vblk);
+out:
+        return err;
+}
+
+static void virtblk_remove(struct virtio_device *vdev)
+{
+        struct virtio_blk *vblk = vdev->priv;
+        int major = vblk->disk->major;
+
+        BUG_ON(!list_empty(&vblk->reqs));
+        blk_cleanup_queue(vblk->disk->queue);
+        put_disk(vblk->disk);
+        unregister_blkdev(major, "virtblk");
+        mempool_destroy(vblk->pool);
+        kfree(vblk);
+}
+
+static struct virtio_device_id id_table[] = {
+        { VIRTIO_ID_BLOCK, VIRTIO_DEV_ANY_ID },
+        { 0 },
+};
+
+static struct virtio_driver virtio_blk = {
+        .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)
+{
+        return register_virtio_driver(&virtio_blk);
+}
+
+static void __exit fini(void)
+{
+        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");
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index b101588a4b5a..6a65231bc785 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -344,6 +344,7 @@ unifdef-y += utsname.h
 unifdef-y += videodev2.h
 unifdef-y += videodev.h
 unifdef-y += virtio_config.h
+unifdef-y += virtio_blk.h
 unifdef-y += virtio_net.h
 unifdef-y += wait.h
 unifdef-y += wanrouter.h
diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
new file mode 100644
index 000000000000..7bd2bce0cfd9
--- /dev/null
+++ b/include/linux/virtio_blk.h
@@ -0,0 +1,51 @@
+#ifndef _LINUX_VIRTIO_BLK_H
+#define _LINUX_VIRTIO_BLK_H
+#include <linux/virtio_config.h>
+
+/* The ID for virtio_block */
+#define VIRTIO_ID_BLOCK 2
+
+/* Feature bits */
+#define VIRTIO_CONFIG_BLK_F     0x40
+#define VIRTIO_BLK_F_BARRIER    1       /* Does host support barriers? */
+
+/* The capacity (in 512-byte sectors). */
+#define VIRTIO_CONFIG_BLK_F_CAPACITY    0x41
+/* The maximum segment size. */
+#define VIRTIO_CONFIG_BLK_F_SIZE_MAX    0x42
+/* The maximum number of segments. */
+#define VIRTIO_CONFIG_BLK_F_SEG_MAX     0x43
+
+/* These two define direction. */
+#define VIRTIO_BLK_T_IN         0
+#define VIRTIO_BLK_T_OUT        1
+
+/* This bit says it's a scsi command, not an actual read or write. */
+#define VIRTIO_BLK_T_SCSI_CMD   2
+
+/* Barrier before this op. */
+#define VIRTIO_BLK_T_BARRIER    0x80000000
+
+/* This is the first element of the read scatter-gather list. */
+struct virtio_blk_outhdr
+{
+        /* VIRTIO_BLK_T* */
+        __u32 type;
+        /* io priority. */
+        __u32 ioprio;
+        /* Sector (ie. 512 byte offset) */
+        __u64 sector;
+        /* Where to put reply. */
+        __u64 id;
+};
+
+#define VIRTIO_BLK_S_OK         0
+#define VIRTIO_BLK_S_IOERR      1
+#define VIRTIO_BLK_S_UNSUPP     2
+
+/* This is the first element of the write scatter-gather list */
+struct virtio_blk_inhdr
+{
+        unsigned char status;
+};
+#endif /* _LINUX_VIRTIO_BLK_H */