Comment 2 for bug 524434

kvm command line as generated by libvirt-bin

/usr/bin/kvm -S -M pc-0.11 -enable-kvm -m 1024 -smp 2,sockets=2,cores=1,threads=1 -name BT -uuid 7e4c5cc4-f077-e52e-6d2d-f865637e87df -nodefaults -chardev socket,id=monitor,path=/var/lib/libvirt/qemu/BT.monitor,server,nowait -mon chardev=monitor,mode=readline -rtc base=utc -boot cd -device lsi,id=scsi0,bus=pci.0,addr=0x6 -drive file=/local/vimages/isos/ubuntu/lucid-alternate-amd64.iso,if=none,media=cdrom,id=drive-ide0-1-0 -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -drive file=/dev/greasy-vg/bt,if=none,id=drive-virtio-disk0,boot=on,format=raw -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,id=virtio-disk0 -device e1000,vlan=0,id=net0,mac=54:52:00:33:9c:2d,bus=pci.0,addr=0x4 -net tap,fd=46,vlan=0,name=hostnet0 -chardev pty,id=serial0 -device isa-serial,chardev=serial0 -usb -vnc 127.0.0.1:0 -k en-us -vga cirrus -device ES1370,id=sound0,bus=pci.0,addr=0x5 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3

Some history and quirks.

1) This system has had the virtual disk swapped to SCSI and back to virtio.

2) grub-pc postinst fails after a switch from SCSI to virtio with cannot find /dev/disk/by-id/....
(There is *NO* /dev/disk/by-id with virtio)

3) After purging grub-pc and reinstalling it, the postinst can no longer find a disk where grub should be installed.

4) grub-install --recheck /dev/vda works just fine

Thoughts.
1) udev persistent storage rules probably need to match the [vs]d*[!0-9] wildmat instead of sd*[!0-9].
2) Until udev is fixed, it would be pleasant if grub-pc.postinst would fallback to /dev/disk/by-uuid.
I think this does it.
available_ids()
{
  local id path diskby

  if [ "$cached_available_ids" ]; then
    echo "$cached_available_ids"
    return
  fi

  for diskby in /dev/disk/by-id /dev/disk/by-uuid; do
    [ -d "$diskby" ] && break
  done
  cached_available_ids="$(
    for path in "$diskby"/* ; do
      [ -e "$path" ] || continue
      printf '%s %s\n' "$path" "$(readlink -f "$path")"
    done | sort -k2 -s -u | cut -d' ' -f1
  )"
  echo "$cached_available_ids"
}
3) Yes, I know testing is a pain, but it's probably worth checking that install works with kvm with all three possible ways of providing disk.