Re: [PATCH v7 29/47] blockdev: Use CAF in external_snapshot_prepare()

[Andrey Shinkevich]

On 25.06.2020 18:21, 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 <mreitz@redhat.com>
> ---
>   blockdev.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index 1eb0fcdea2..aabe51036d 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1549,7 +1549,12 @@ static void external_snapshot_prepare(BlkActionState 
> *common,
>           goto out;
>       }
>   
> -    if (state->new_bs->backing != NULL) {
> +    if (state->new_bs->drv->is_filter) {


Is there a chance to get a filter here? If so, is that when a user 
specifies the file name of such a kind “filter[filter-name]:foo.qcow2” 
or somehow else?

Andrey


> +        error_setg(errp, "Filters cannot be used as overlays");
> +        goto out;
> +    }
> +
> +    if (bdrv_cow_child(state->new_bs)) {
>           error_setg(errp, "The overlay already has a backing image");
>           goto out;
>       }


Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>