block snapshot issue with RBD

[Jin Cao <jojing64@gmail.com>]

Hi,

I encountered RBD block snapshot issue after doing migration.

Steps
-----

1. Start QEMU with:
./qemu-system-x86_64 -name VM -machine q35 -accel kvm -cpu 
host,migratable=on -m 2G -boot menu=on,strict=on 
rbd:image/ubuntu-22.04-server-cloudimg-amd64.raw -net nic -net user 
-cdrom /home/my/path/of/cloud-init.iso -monitor stdio

2. Do block snapshot in monitor cmd: snapshot_delete_blkdev_internal. It 
works as expected: the snapshot is visable with command`rbd snap ls 
pool_name/image_name`.

3. Do pseudo migration with monitor cmd: migrate -d exec:cat>/tmp/vm.out

4. Do block snapshot again with snapshot_delete_blkdev_internal, then I get:
    Error: Block format 'raw' used by device 'ide0-hd0' does not support 
internal snapshots

I was hoping to do the second block snapshot successfully, and it feels 
abnormal the RBD block snapshot function is disrupted after migration.

BTW, I get the same block snapshot error when I start QEMU with:
     "-drive format=raw,file=rbd:pool_name/image_name"

My questions is: how could I proceed with RBD block snapshot after the 
pseudo migration?