[Qemu-devel] [PATCH 3/8] virtio-blk: fix barrier support

[Kevin Wolf <kwolf@redhat.com>]

From: Christoph Hellwig <hch@lst.de>

Before issuing the barrier to the block driver we need to flush our oustanding
queue of write requests, as the flush is supposed to be issued after them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/virtio-blk.c |   15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index d270225..5d7f1a2 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -240,10 +240,20 @@ static void do_multiwrite(BlockDriverState *bs, BlockRequest *blkreq,
     }
 }
 
-static void virtio_blk_handle_flush(VirtIOBlockReq *req)
+static void virtio_blk_handle_flush(BlockRequest *blkreq, int *num_writes,
+    VirtIOBlockReq *req, BlockDriverState **old_bs)
 {
     BlockDriverAIOCB *acb;
 
+    /*
+     * Make sure all outstanding writes are posted to the backing device.
+     */
+    if (*old_bs != NULL) {
+        do_multiwrite(*old_bs, blkreq, *num_writes);
+    }
+    *num_writes = 0;
+    *old_bs = req->dev->bs;
+
     acb = bdrv_aio_flush(req->dev->bs, virtio_blk_flush_complete, req);
     if (!acb) {
         virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
@@ -316,7 +326,8 @@ static void virtio_blk_handle_request(VirtIOBlockReq *req,
     req->in = (void *)req->elem.in_sg[req->elem.in_num - 1].iov_base;
 
     if (req->out->type & VIRTIO_BLK_T_FLUSH) {
-        virtio_blk_handle_flush(req);
+        virtio_blk_handle_flush(mrb->blkreq, &mrb->num_writes,
+            req, &mrb->old_bs);
     } else if (req->out->type & VIRTIO_BLK_T_SCSI_CMD) {
         virtio_blk_handle_scsi(req);
     } else if (req->out->type & VIRTIO_BLK_T_OUT) {
-- 
1.6.6.1