Re: [Qemu-devel] [PATCH v5 23/42] blockdev: Use CAF in external_snapshot_prepare()

[Vladimir Sementsov-Ogievskiy]

13.06.2019 1:09, Max Reitz wrote:
> This allows us to differentiate between filters and nodes with COW
> backing files: Filters cannot be used as overlays at all (for this
> function).
> 
> Signed-off-by: Max Reitz <address@hidden>

Overlay created in snapshot operation assumed to consume following writes
and it's filtered child becomes readonly.. And filter works in completely 
another
way.

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

[hmm, I start to like using "filtered child" collocation when I say about this 
thing.
  didn't you think about renaming backing chain to filtered chain?]

> ---
>   blockdev.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index b5c0fd3c49..0f0cf0d9ae 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1665,7 +1665,12 @@ static void external_snapshot_prepare(BlkActionState 
> *common,
>           goto out;
>       }
>   
> -    if (state->new_bs->backing != NULL) {
> +    if (state->new_bs->drv->is_filter) {
> +        error_setg(errp, "Filters cannot be used as overlays");
> +        goto out;
> +    }
> +
> +    if (bdrv_filtered_cow_child(state->new_bs)) {
>           error_setg(errp, "The overlay already has a backing image");
>           goto out;
>       }
> 


-- 
Best regards,
Vladimir