Comment 1 for bug 552998

The problem with block devices exposed using virtio in kvm is that they look quite similar according to udevadm. For example, the following devices are supposed to be a virtual hard drive and cdrom respectively:

$ udevadm info -q env -p /block/vda
UDEV_LOG=3
DEVPATH=/devices/virtio-pci/virtio1/block/vda
MAJOR=252
MINOR=0
DEVNAME=/dev/vda
DEVTYPE=disk
SUBSYSTEM=block
ID_PART_TABLE_TYPE=dos
DEVLINKS=/dev/block/252:0

$ udevadm info -q env -p /block/vdb
UDEV_LOG=3
DEVPATH=/devices/virtio-pci/virtio2/block/vdb
MAJOR=252
MINOR=16
DEVNAME=/dev/vdb
DEVTYPE=disk
SUBSYSTEM=block
ID_FS_LABEL=Ubuntu-Server_10.04_i386
ID_FS_LABEL_ENC=Ubuntu-Server\x2010.04\x20i386
ID_FS_TYPE=iso9660
ID_FS_USAGE=filesystem
DEVLINKS=/dev/block/252:16 /dev/disk/by-label/Ubuntu-Server\x2010.04\x20i386