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 <mre...@redhat.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
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
>
