On 10.09.19 17:02, Kevin Wolf wrote: > 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?
I can only remember advertising for it as the only graph manipulation
tool we had, and maybe saying “We’d want something like
blockdev-snapshot for filters, too”.
Max
> 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
>>
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