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 <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?
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