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authorChristoph Hellwig <hch@lst.de>2009-09-17 19:57:42 +0200
committerRusty Russell <rusty@rustcorp.com.au>2009-09-23 22:26:36 +0930
commitf1b0ef062602713c2c7cfa12362d5d90ed01c5f6 (patch)
tree30a130141b7c4b69ff20d134734acd40f1ee0960
parent3ca4f5ca73057a617f9444a91022d7127041970a (diff)
virtio_blk: add support for cache flush
Recent qemu has added a VIRTIO_BLK_F_FLUSH flag to advertise that the virtual disk has a volatile write cache that needs to be flushed. In case we see this feature implement tell the Linux block layer about the fact and use the new VIRTIO_BLK_T_FLUSH to flush the cache when required. This allows for an correct and simple implementation of write barriers. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--drivers/block/virtio_blk.c30
-rw-r--r--include/linux/virtio_blk.h15
2 files changed, 40 insertions, 5 deletions
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 73de7532fcf..3d5fe97569c 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -92,15 +92,26 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
return false;
vbr->req = req;
- if (blk_fs_request(vbr->req)) {
+ 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);
- } else if (blk_pc_request(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);
- } else {
+ break;
+ case REQ_TYPE_LINUX_BLOCK:
+ if (req->cmd[0] == REQ_LB_OP_FLUSH) {
+ vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;
+ vbr->out_hdr.sector = 0;
+ vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);
+ break;
+ }
+ /*FALLTHRU*/
+ default:
/* We don't put anything else in the queue. */
BUG();
}
@@ -200,6 +211,12 @@ out:
return err;
}
+static void virtblk_prepare_flush(struct request_queue *q, struct request *req)
+{
+ req->cmd_type = REQ_TYPE_LINUX_BLOCK;
+ req->cmd[0] = REQ_LB_OP_FLUSH;
+}
+
static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
unsigned cmd, unsigned long data)
{
@@ -338,7 +355,10 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
index++;
/* If barriers are supported, tell block layer that queue is ordered */
- if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
+ if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+ blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_DRAIN_FLUSH,
+ virtblk_prepare_flush);
+ else 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 */
@@ -425,7 +445,7 @@ static struct virtio_device_id id_table[] = {
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
+ VIRTIO_BLK_F_SCSI, VIRTIO_BLK_F_IDENTIFY, VIRTIO_BLK_F_FLUSH
};
/*
diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
index 25fbabfa90d..15cb666581d 100644
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -14,6 +14,7 @@
#define VIRTIO_BLK_F_BLK_SIZE 6 /* Block size of disk is available*/
#define VIRTIO_BLK_F_SCSI 7 /* Supports scsi command passthru */
#define VIRTIO_BLK_F_IDENTIFY 8 /* ATA IDENTIFY supported */
+#define VIRTIO_BLK_F_FLUSH 9 /* Cache flush command support */
#define VIRTIO_BLK_ID_BYTES (sizeof(__u16[256])) /* IDENTIFY DATA */
@@ -35,6 +36,17 @@ struct virtio_blk_config {
__u8 identify[VIRTIO_BLK_ID_BYTES];
} __attribute__((packed));
+/*
+ * Command types
+ *
+ * Usage is a bit tricky as some bits are used as flags and some are not.
+ *
+ * Rules:
+ * VIRTIO_BLK_T_OUT may be combined with VIRTIO_BLK_T_SCSI_CMD or
+ * VIRTIO_BLK_T_BARRIER. VIRTIO_BLK_T_FLUSH is a command of its own
+ * and may not be combined with any of the other flags.
+ */
+
/* These two define direction. */
#define VIRTIO_BLK_T_IN 0
#define VIRTIO_BLK_T_OUT 1
@@ -42,6 +54,9 @@ struct virtio_blk_config {
/* This bit says it's a scsi command, not an actual read or write. */
#define VIRTIO_BLK_T_SCSI_CMD 2
+/* Cache flush command */
+#define VIRTIO_BLK_T_FLUSH 4
+
/* Barrier before this op. */
#define VIRTIO_BLK_T_BARRIER 0x80000000