[Qemu-devel] [PATCH] block: Flush image after open

[Kevin Wolf <kwolf@redhat.com>]

Quoting the bug report:

    qemu ensures that guest writes and qemu metadata writes hit the disk
    when necessary to prevent data corruption. However, if an image was
    in host pagecache prior to starting qemu, for example after running
    qemu-img convert, then nothing prevents writes from reaching the
    disk out of order, potentially causing corruption.

I'm not entirely sure if there is a realistic case where we would get
corruption, but it's probably a case of better safe than sorry.

Reported-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index 8dea0b5..bf6892f 100644
--- a/block.c
+++ b/block.c
@@ -648,6 +648,14 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
     }
 
+    /* Make sure that the image is consistent on disk */
+    if (!bdrv_is_read_only(bs)) {
+        ret = bdrv_flush(bs);
+        if (ret < 0) {
+            goto unlink_and_fail;
+        }
+    }
+
     return 0;
 
 unlink_and_fail:
-- 
1.7.2.3