commit snapshot image got Permission denied error

qemu 2.9.0, adm64, start image with -snapshot param, make some changes in the image, then:

$telnet localhost 7000

(qemu) commit virtio0
'commit' error for 'virtio0': Permission denied

Nerver met this problem before, commit is ok. I recently compiled v2.9.0, so is there some new param in qemu-qemu-system-x86_64 to avoid commit Permission denied?

Regards.