[PATCH 4/6] virtio block driver

Rusty Russell
2007-09-20T12:16:46Z

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, the block
layer in its infinite wisdom suppressed the error so ioctl(fd,
CDROMEJECT) returns success to userspace.

Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
---
drivers/block/Kconfig | 6
drivers/block/Makefile | 1
drivers/block/virtio_blk.c | 327 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/Kbuild | 1
include/linux/virtio_blk.h | 51 ++++++
5 files changed, 386 insertions(+)

===================================================================
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -443,4 +443,10 @@ 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
===================================================================
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_BLK_DEV_UMEM) += umem.o
obj-$(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
===================================================================
--- /dev/null
+++ b/drivers/block/virtio_blk.c
@@ -0,0 +1,327 @@
+#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 virtqueue *vq;
+ struct virtqueue_ops *vq_ops;
+
+ /* 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 void end_dequeued_request(struct request *req,
+ struct request_queue *q, int uptodate)
+{
+ /* And so the insanity of the block layer infects us here. */
+ int nsectors = req->hard_nr_sectors;
+
+ if (blk_pc_request(req)) {
+ nsectors = (req->data_len + 511) >> 9;
+ if (!nsectors)
+ nsectors = 1;
+ }
+ if (end_that_request_first(req, uptodate, nsectors))
+ BUG();
+ add_disk_randomness(req->rq_disk);
+ end_that_request_last(req, uptodate);
+}
+
+static bool blk_done(void *_vblk)
+{
+ struct virtio_blk *vblk = _vblk;
+ struct virtblk_req *vbr;
+ unsigned int len;
+ unsigned long flags;
+
+ spin_lock_irqsave(&vblk->lock, flags);
+ while ((vbr = vblk->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, vblk->disk->queue, 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_num, in_num;
+ 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;
+
+ vblk->sg[0].page = virt_to_page(&vbr->out_hdr);
+ vblk->sg[0].offset = offset_in_page(&vbr->out_hdr);
+ vblk->sg[0].length = sizeof(vbr->out_hdr);
+ num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
+ vblk->sg[num+1].page = virt_to_page(&vbr->in_hdr);
+ vblk->sg[num+1].offset = offset_in_page(&vbr->in_hdr);
+ vblk->sg[num+1].length = sizeof(vbr->in_hdr);
+
+ if (rq_data_dir(vbr->req) == WRITE) {
+ vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
+ out_num = 1 + num;
+ in_num = 1;
+ } else {
+ vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
+ out_num = 1;
+ in_num = 1 + num;
+ }
+
+ if (vblk->vq_ops->add_buf(vblk->vq, vblk->sg, out_num, in_num, 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 (!do_req(q, vblk, req)) {
+ /* Queue full? Wait. */
+ blk_stop_queue(q);
+ break;
+ }
+ blkdev_dequeue_request(req);
+ issued++;
+ }
+
+ if (issued)
+ vblk->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 void *virtblk_probe(struct device *device,
+ struct virtio_config_space *config,
+ struct virtqueue_ops *vq_ops)
+{
+ struct virtio_blk *vblk;
+ int err, major, coff;
+ unsigned int len;
+ u64 cap;
+ u32 v;
+
+ vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+ if (!vblk) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ INIT_LIST_HEAD(&vblk->reqs);
+ spin_lock_init(&vblk->lock);
+ vblk->vq_ops = vq_ops;
+
+ /* We expect one virtqueue, for output. */
+ vblk->vq = virtio_config_vq(config, vq_ops, device, blk_done, vblk);
+ 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 */
+ coff = virtio_config_find(config, VIRTIO_CONFIG_BLK_F, &len);
+ if (virtio_use_bit(config, coff, len, VIRTIO_BLK_F_BARRIER))
+ blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);
+
+ err = virtio_config_val(config, VIRTIO_CONFIG_BLK_F_CAPACITY, &cap);
+ if (err) {
+ dev_err(device, "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(device, "Capacity %llu is too large: truncating\n",
+ (unsigned long long)cap);
+ cap = (sector_t)-1;
+ }
+ set_capacity(vblk->disk, cap);
+
+ err = virtio_config_val(config, VIRTIO_CONFIG_BLK_F_SIZE_MAX, &v);
+ if (!err)
+ blk_queue_max_segment_size(vblk->disk->queue, v);
+ else if (err != -ENOENT) {
+ dev_err(device, "Bad SIZE_MAX in config\n");
+ goto out_put_disk;
+ }
+
+ err = virtio_config_val(config, VIRTIO_CONFIG_BLK_F_SEG_MAX, &v);
+ if (!err)
+ blk_queue_max_hw_segments(vblk->disk->queue, v);
+ else if (err != -ENOENT) {
+ dev_err(device, "Bad SEG_MAX in config\n");
+ goto out_put_disk;
+ }
+
+ add_disk(vblk->disk);
+ return vblk;
+
+out_put_disk:
+ put_disk(vblk->disk);
+out_unregister_blkdev:
+ unregister_blkdev(major, "virtblk");
+out_mempool:
+ mempool_destroy(vblk->pool);
+out_free_vq:
+ vq_ops->free_vq(vblk->vq);
+out_free_vblk:
+ kfree(vblk);
+out:
+ return ERR_PTR(err);
+}
+
+static void virtblk_remove(void *_vblk)
+{
+ struct virtio_blk *vblk = _vblk;
+ 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 pci_device_id id_table[] = {
+ VIRTIO_DEV_ID(VIRTIO_ID_BLOCK, PCI_CLASS_STORAGE_OTHER),
+ { 0 },
+};
+
+static struct virtio_driver virtio_blk = {
+ .name = KBUILD_MODNAME,
+ .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(pci, id_table);
+MODULE_DESCRIPTION("Virtio block driver");
+MODULE_LICENSE("GPL");
===================================================================
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -343,6 +343,7 @@ unifdef-y += utsname.h
unifdef-y += utsname.h
unifdef-y += videodev2.h
unifdef-y += videodev.h
+unifdef-y += virtio_blk.h
unifdef-y += wait.h
unifdef-y += wanrouter.h
unifdef-y += watchdog.h
===================================================================
--- /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 */