[libvirt] bug: try to take disk snapshot for LVM2 Volume

I tried the new snapshot function implemented by Eric Blake. It works very well for QCOW2 disk image system. But I often use LVM2 volume for QEMU virtual machines and tried to take disk snapshot by virsh command ( snapshot-create DOMNAME --disk-only). So, finally qemu monitor command 'snapshot_blkdev' accepts the LVM2 volume and create QCOW2 snapshot image. In addition, domain's configuration file is replaced to use snapshot disk image instead of LVM2 volume. configuration file from .... <disk type='block' device='disk> <driver name='qemu' type='raw' cache='none'/> <source dev='dev/VG1/LVM2_dom'/> .... to <disk type='block' device='disk> <driver name='qemu' type='qcow2' cache='none'/> <source dev='dev/VG1/LVM2_dom.1317357844'/> After then, the domain runs well till it is shutdowned. I started the domain, but it does not with following error virtsh # start LVM2_dom error: Failed to start domain LVM2_dom error: 内部エラー Process exited while reading console log output: char device redirected to /dev/pts/7 qemu: could not open disk image /dev/VG1/LVM2_dom.1317357844: Invalid argument. I think that if the volume but qcow2 is given libvirt should be refuse, e.g. in qemuDomainSnapshotCreateDiskActive() with voulme driver type. But currently the structures concerning with snapshot or disk has no member to hold such a volume driver information. In addition, as we want to add the LVM2 and other volume snapshot function, we hope you add its information and fix. Regards MATSUDA Daiki