block: BDRV_O_NO_IO for backing file on creation
When creating an image file with a backing file, we generally try to
open the backing file (unless -u was specified), mostly to verify that
it is there, but also to get the file size if none was specified for the
new image.
For neither of these things do we need data I/O, and so we can pass
BDRV_O_NO_IO when opening the backing file. This allows us to open even
encrypted backing images without requiring the user to provide a secret.
This makes the -u switch in iotests 189 and 198 unnecessary (and the
$size parameter), so drop it, because this way we get regression tests
for this patch here.
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/441
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210622140030.212487-1-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 3e27785..a2a4a0d 100644
--- a/block.c
+++ b/block.c
@@ -6553,9 +6553,13 @@
}
assert(full_backing);
- /* backing files always opened read-only */
+ /*
+ * No need to do I/O here, which allows us to open encrypted
+ * backing images without needing the secret
+ */
back_flags = flags;
back_flags &= ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
+ back_flags |= BDRV_O_NO_IO;
backing_options = qdict_new();
if (backing_fmt) {
