On 20.07.20 18:08, Andrey Shinkevich wrote: > 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 <mre...@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?
It would be with blockdev-snapshot and by specifying a filter for @overlay. Technically that’s already caught by the check whether the overlay supports backing images (whether drv->supports_backing is true), but we might as well give a nicer error message. Example: {"execute":"qmp_capabilities"} {"execute":"blockdev-add","arguments": {"node-name":"overlay","driver":"copy-on-read", "file":{"driver":"null-co"}}} {"execute":"blockdev-add","arguments": {"node-name":"base","driver":"null-co"}} {"execute":"blockdev-snapshot","arguments": {"node":"base","overlay":"overlay"}} Max
signature.asc
Description: OpenPGP digital signature