block: Disable BDRV_O_COPY_ON_READ for the backing file

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>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block.c b/block.c
index 366999b15c067a33e204019ba0ec5bd8b1432afd..61795fea46401fe7677d82556ed54204e9fafb56 100644 (file)
--- 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,