Re: [Qemu-devel] [PATCH] commit: get the overlay node before manipulating the backing chain

[Max Reitz]

On 2016-08-21 at 23:36, Alberto Garcia wrote:
> The 'block-commit' command has a 'top' parameter to specify the
> topmost node from which the data is going to be copied.
>
>    [E] <- [D] <- [C] <- [B] <- [A]
>
> In this case if [C] is the top node then this is the result:
>
>    [E] <- [B] <- [A]
>
> [B] must be modified so its backing image string points to [E] instead
> of [C]. commit_start() takes care of reopening [B] in read-write
> mode, and commit_complete() puts it back in read-only mode once the
> operation has finished.
>
> In order to find [B] (the overlay node) we look for the node that has
> [C] (the top node) as its backing image. However in commit_complete()
> we're doing it after [C] has been removed from the chain, so [B] is
> never found and remains in read-write mode.

That's... Unfortunate.

> This patch gets the overlay node before the backing chain is
> manipulated.
>
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/commit.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Thanks, applied to my block-next tree:

https://github.com/XanClic/qemu/commits/block-next

Max