commit: reopen overlay_bs before base
'block-commit' needs write access to two different nodes of the chain:
- 'base', because that's where the data is written to.
- the overlay of 'top', because it needs to update the backing file
string to point to 'base' after the operation.
Both images have to be opened in read-write mode, and commit_start()
takes care of reopening them if necessary.
With the current implementation, however, when overlay_bs is reopened
in read-write mode it has the side effect of making 'base' read-only
again, eventually making 'block-commit' fail.
This needs to be fixed in bdrv_reopen(), but until we get to that it
can be worked around simply by swapping the order of base and
overlay_bs in the reopen queue.
In order to reproduce this bug, overlay_bs needs to be initially in
read-only mode. That is: the 'top' parameter of 'block-commit' cannot
be the active layer nor its immediate backing chain.
Cc: qemu-stable@nongnu.org
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
1 file changed
