On Fri, 06/10 20:57, Max Reitz wrote:
> change_parent_backing_link() asserts that the BDS to be replaced is not
> used as a backing file. However, we may want to replace a BDS by its
> overlay in which case that very link should not be redirected.
>
> For instance, when doing a sync=none drive-mirror operation, we may have
> the following BDS/BB forest before block job completion:
>
> target
>
> base <- source <- BlockBackend
>
> During job completion, we want to establish the source BDS as the
> target's backing node:
>
> target
> |
> v
> base <- source <- BlockBackend
>
> This makes the target a valid replacement for the source:
>
> target <- BlockBackend
> |
> v
> base <- source
>
> Without this modification to change_parent_backing_link() we have to
> inject the target into the graph before the source is its backing node,
> thus temporarily creating a wrong graph:
>
> target <- BlockBackend
>
> base <- source
>
> Signed-off-by: Max Reitz <[email protected]>
> ---
> block.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index f54bc25..dc76c159 100644
> --- a/block.c
> +++ b/block.c
> @@ -2224,9 +2224,23 @@ void bdrv_close_all(void)
> static void change_parent_backing_link(BlockDriverState *from,
> BlockDriverState *to)
> {
> - BdrvChild *c, *next;
> + BdrvChild *c, *next, *to_c;
>
> QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
> + if (c->role == &child_backing) {
> + /* @from is generally not allowed to be a backing file, except
> for
> + * when @to is the overlay. In that case, @from may not be
> replaced
> + * by @to as @to's backing node. */
> + QLIST_FOREACH(to_c, &to->children, next) {
> + if (to_c == c) {
> + break;
> + }
> + }
Why not just test "c->bs == to" here, why is it necessary to iterate through
to->children list?
Fam
> + if (to_c) {
> + continue;
> + }
> + }
> +
> assert(c->role != &child_backing);
> bdrv_ref(to);
> bdrv_replace_child(c, to);
> --
> 2.8.3
>
