Re: [Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare()

[Kevin Wolf]

Am 09.08.2019 um 18:13 hat Max Reitz geschrieben:
> 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>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

Didn't we occasionally advertise blockdev-snapshot as the way to insert
filters on top at runtime? Though it seems it has always only worked for
filters that use bs->backing, among which I think there aren't any
user-creatable ones. So we're probably good.

Kevin

>  blockdev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 29c6c6044a..c540802127 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1664,7 +1664,12 @@ 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;
>      }
> -- 
> 2.21.0
>