[PATCH RFC 2/3] Virtio draft II: example block driver

Rusty Russell
2007-06-07T12:05:20Z

The block driver uses outbufs with sg[0] being the request information
(struct virtio_blk_outhdr) with the type, sector and inbuf id. For a
write, the rest of the sg will contain the data to be written.

The first segment of the inbuf is a result code (struct
virtio_blk_inhdr). For a read, the rest of the sg points to the input
buffer.

TODO:
1) Ordered tag support.

Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
---
drivers/block/Makefile | 1
drivers/block/virtio_blk.c | 299 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/virtio_blk.h | 28 ++++
3 files changed, 328 insertions(+)

===================================================================
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_BLK_CPQ_CISS_DA) += cciss.
obj-$(CONFIG_BLK_CPQ_CISS_DA) += cciss.o
obj-$(CONFIG_BLK_DEV_DAC960) += DAC960.o
obj-$(CONFIG_CDROM_PKTCDVD) += pktcdvd.o
+obj-y += virtio_blk.o

obj-$(CONFIG_BLK_DEV_UMEM) += umem.o
obj-$(CONFIG_BLK_DEV_NBD) += nbd.o
===================================================================
--- /dev/null
+++ b/drivers/block/virtio_blk.c
@@ -0,0 +1,299 @@
+//#define DEBUG
+#include <linux/spinlock.h>
+#include <linux/blkdev.h>
+#include <linux/hdreg.h>
+#include <linux/virtio.h>
+#include <linux/virtio_blk.h>
+
+static unsigned char virtblk_index = 'a';
+struct virtio_blk
+{
+ struct virtio_device *vdev;
+
+ /* 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[1+MAX_PHYS_SEGMENTS];
+};
+
+struct virtblk_req
+{
+ struct list_head list;
+ struct request *req;
+ unsigned long out_id;
+ bool out_done, in_done;
+ bool failed;
+ struct virtio_blk_outhdr out_hdr;
+ struct virtio_blk_inhdr in_hdr;
+};
+
+/* Jens gave me this nice helper to end all chunks of a request. */
+static void end_dequeued_request(struct request *req, int uptodate)
+{
+ if (end_that_request_first(req, uptodate, req->hard_nr_sectors))
+ BUG();
+ add_disk_randomness(req->rq_disk);
+ end_that_request_last(req, uptodate);
+}
+
+static void finish(struct virtio_blk *vblk, struct virtblk_req *vbr)
+{
+ end_dequeued_request(vbr->req, !vbr->failed);
+ list_del(&vbr->list);
+ mempool_free(vbr, vblk->pool);
+ /* In case queue is stopped waiting for more buffers. */
+ blk_start_queue(vblk->disk->queue);
+}
+
+/* We make sure they finished both the input and output buffers: otherwise
+ * they might still have read access after we free them. */
+static void blk_out_done(struct virtio_device *vdev, void *_vbr, unsigned len)
+{
+ struct virtblk_req *vbr = _vbr;
+ struct virtio_blk *vblk = vdev->priv;
+
+ assert_spin_locked(&vblk->vdev->lock);
+
+ BUG_ON(vbr->out_done);
+ vbr->out_done = true;
+ if (vbr->in_done)
+ finish(vblk, vbr);
+}
+
+static void blk_in_done(struct virtio_device *vdev, void *_vbr, unsigned len)
+{
+ struct virtblk_req *vbr = _vbr;
+ struct virtio_blk *vblk = vdev->priv;
+ unsigned long expected_len;
+
+ assert_spin_locked(&vblk->vdev->lock);
+
+ expected_len = sizeof(vbr->in_hdr);
+ if (vbr->out_hdr.type == READ)
+ expected_len += vbr->req->hard_nr_sectors*512;
+
+ if (unlikely(len != expected_len)) {
+ dev_err(vblk->vdev->dev, "short reply %u not %lu",
+ len, expected_len);
+ vbr->failed = true;
+ } else if (unlikely(vbr->in_hdr.status != 1)) {
+ vbr->failed = true;
+ }
+
+ BUG_ON(vbr->in_done);
+ vbr->in_done = true;
+ if (vbr->out_done)
+ finish(vblk, vbr);
+}
+
+static bool do_write(request_queue_t *q, struct virtio_blk *vblk,
+ struct virtblk_req *vbr)
+{
+ unsigned long num;
+
+ /* Set up for reply. */
+ vblk->sg[0].page = virt_to_page(&vbr->in_hdr);
+ vblk->sg[0].offset = offset_in_page(&vbr->in_hdr);
+ vblk->sg[0].length = sizeof(vbr->in_hdr);
+ vbr->out_hdr.id = vblk->vdev->ops->add_inbuf(vblk->vdev, vblk->sg, 1,
+ blk_in_done, vbr);
+ if (IS_ERR_VALUE(vbr->out_hdr.id))
+ goto full;
+
+ /* First sg element points to output header. */
+ 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);
+ vbr->out_done = vbr->in_done = false;
+ vbr->failed = false;
+ vbr->out_id = vblk->vdev->ops->add_outbuf(vblk->vdev, vblk->sg, 1+num,
+ blk_out_done, vbr);
+ if (IS_ERR_VALUE(vbr->out_id))
+ goto detach_inbuf_full;
+
+ pr_debug("Write: %p in=%lu out=%lu\n", vbr,
+ vbr->out_hdr.id, vbr->out_id);
+ list_add_tail(&vbr->list, &vblk->reqs);
+ return true;
+
+detach_inbuf_full:
+ vblk->vdev->ops->detach_inbuf(vblk->vdev, vbr->out_hdr.id);
+full:
+ return false;
+}
+
+static bool do_read(request_queue_t *q, struct virtio_blk *vblk,
+ struct virtblk_req *vbr)
+{
+ unsigned long num;
+
+ /* Set up for reply. */
+ vblk->sg[0].page = virt_to_page(&vbr->in_hdr);
+ vblk->sg[0].offset = offset_in_page(&vbr->in_hdr);
+ vblk->sg[0].length = sizeof(vbr->in_hdr);
+ num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
+ vbr->out_hdr.id = vblk->vdev->ops->add_inbuf(vblk->vdev, vblk->sg,
+ 1+num, blk_in_done, vbr);
+ if (IS_ERR_VALUE(vbr->out_hdr.id))
+ goto full;
+
+ 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);
+
+ vbr->out_done = vbr->in_done = false;
+ vbr->failed = false;
+ vbr->out_id = vblk->vdev->ops->add_outbuf(vblk->vdev, vblk->sg, 1,
+ blk_out_done, vbr);
+ if (IS_ERR_VALUE(vbr->out_id))
+ goto detach_inbuf_full;
+
+ pr_debug("Read: %p in=%lu out=%lu\n", vbr,
+ vbr->out_hdr.id, vbr->out_id);
+ list_add_tail(&vbr->list, &vblk->reqs);
+ return true;
+
+detach_inbuf_full:
+ vblk->vdev->ops->detach_inbuf(vblk->vdev, vbr->out_hdr.id);
+full:
+ return false;
+}
+
+static void do_virtblk_request(request_queue_t *q)
+{
+ struct virtio_blk *vblk = NULL;
+ struct request *req;
+ struct virtblk_req *vbr;
+
+ while ((req = elv_next_request(q)) != NULL) {
+ vblk = req->rq_disk->private_data;
+
+ /* FIXME: handle these iff capable. */
+ if (!blk_fs_request(req)) {
+ pr_debug("Got non-command 0x%08x\n", req->cmd_type);
+ req->errors++;
+ blkdev_dequeue_request(req);
+ end_dequeued_request(req, 0);
+ continue;
+ }
+
+ vbr = mempool_alloc(vblk->pool, GFP_ATOMIC);
+ if (!vbr)
+ goto stop;
+
+ BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg));
+ vbr->req = req;
+ vbr->out_hdr.type = rq_data_dir(req);
+ vbr->out_hdr.sector = req->sector;
+
+ if (rq_data_dir(req) == WRITE) {
+ if (!do_write(q, vblk, vbr))
+ goto stop;
+ } else {
+ if (!do_read(q, vblk, vbr))
+ goto stop;
+ }
+ blkdev_dequeue_request(req);
+ }
+
+sync:
+ if (vblk)
+ vblk->vdev->ops->sync(vblk->vdev);
+ return;
+
+stop:
+ /* Queue full? Wait. */
+ blk_stop_queue(q);
+ mempool_free(vbr, vblk->pool);
+ goto sync;
+}
+
+static struct block_device_operations virtblk_fops = {
+ .owner = THIS_MODULE,
+};
+
+struct gendisk *virtblk_probe(struct virtio_device *vdev)
+{
+ struct virtio_blk *vblk;
+ int err, major;
+
+ vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+ if (!vblk) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ INIT_LIST_HEAD(&vblk->reqs);
+ vblk->vdev = vdev;
+ vdev->priv = vblk;
+
+ vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
+ if (!vblk->pool) {
+ err = -ENOMEM;
+ goto out_free_vblk;
+ }
+
+ 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 << 3);
+ if (!vblk->disk) {
+ err = -ENOMEM;
+ goto out_unregister_blkdev;
+ }
+
+ vblk->disk->queue = blk_init_queue(do_virtblk_request,
+ &vblk->vdev->lock);
+ if (!vblk->disk->queue) {
+ err = -ENOMEM;
+ goto out_put_disk;
+ }
+
+ sprintf(vblk->disk->disk_name, "vb%c", virtblk_index++);
+ vblk->disk->major = major;
+ vblk->disk->first_minor = 0;
+ vblk->disk->private_data = vblk;
+ vblk->disk->fops = &virtblk_fops;
+
+ /* Caller can do blk_queue_max_hw_segments(), set_capacity()
+ * etc then add_disk(). */
+ return vblk->disk;
+
+out_put_disk:
+ put_disk(vblk->disk);
+out_unregister_blkdev:
+ unregister_blkdev(major, "virtblk");
+out_mempool:
+ mempool_destroy(vblk->pool);
+out_free_vblk:
+ kfree(vblk);
+out:
+ return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(virtblk_probe);
+
+void virtblk_remove(struct gendisk *disk)
+{
+ struct virtio_blk *vblk = disk->private_data;
+ 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);
+}
+EXPORT_SYMBOL_GPL(virtblk_remove);
===================================================================
--- /dev/null
+++ b/include/linux/virtio_blk.h
@@ -0,0 +1,28 @@
+#ifndef _LINUX_VIRTIO_BLK_H
+#define _LINUX_VIRTIO_BLK_H
+#include <linux/types.h>
+struct gendisk;
+struct virtio_device;
+struct hd_geometry;
+
+/* This is the first element of the scatter-gather list. */
+struct virtio_blk_outhdr
+{
+ /* 0 == read, 1 == write */
+ u32 type;
+ /* Sector (ie. 512 byte offset) */
+ unsigned long sector;
+ /* Where to put reply. */
+ unsigned long id;
+};
+
+struct virtio_blk_inhdr
+{
+ /* 1 = OK, 0 = not ok. */
+ unsigned long status;
+};
+
+struct gendisk *virtblk_probe(struct virtio_device *vdev);
+void virtblk_remove(struct gendisk *disk);
+
+#endif /* _LINUX_VIRTIO_BLK_H */