block: Allow child references on reopen
In the previous patches we removed all child references from bs->{options,explicit_options} because keeping them is useless and wrong. Because of this, any attempt to reopen a BlockDriverState using a child reference as one of its options would result in a failure, because bdrv_reopen_prepare() would detect that there's a new option (the child reference) that wasn't present in bs->options. But passing child references on reopen can be useful. It's a way to specify a BDS's child without having to pass recursively all of the child's options, and if the reference points to a different BDS then this can allow us to replace the child. However, replacing the child is something that needs to be implemented case by case and only when it makes sense. For now, this patch allows passing a child reference as long as it points to the current child of the BlockDriverState. It's also important to remember that, as a consequence of the previous patches, this child reference will be removed from bs->{options,explicit_options} after the reopening has been completed. Signed-off-by: NAlberto Garcia <berto@igalia.com> Reviewed-by: NMax Reitz <mreitz@redhat.com> Signed-off-by: NKevin Wolf <kwolf@redhat.com>
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