[Qemu-devel] [PATCH] Fix COR by disabling BDRV_O_COPY_ON_READ before opening the backing_file.

[Thibaut LAURENT <thibaut.laurent@gmail.com>]

Since commit 0ebd24e0a203cf2852c310b59fbe050190dc6c8c,
bdrv_open_common will throw an error when trying to open a file
read-only with the BDRV_O_COPY_ON_READ flag set.
Although BDRV_O_RDWR is unset for the backing files,
BDRV_O_COPY_ON_READ is still passed on if copy-on-read was requested
for the drive. Let's unset this flag too before opening the backing
file, or bdrv_open_common will fail.

Signed-off-by: Thibaut LAURENT <thibaut.laurent@gmail.com>
---
 block.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index fd05a80..4474012 100644
--- a/block.c
+++ b/block.c
@@ -999,7 +999,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
     }
 
     /* backing files always opened read-only */
-    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT);
+    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
+                                    BDRV_O_COPY_ON_READ);
 
     ret = bdrv_open(bs->backing_hd,
                     *backing_filename ? backing_filename : NULL, options,
-- 
1.8.4.1