[Qemu-devel] virtio-blk-pci: how to tell if it is CD or HDD?

[Alexey Kardashevskiy]

Hi!

Normally on sPAPR platform the IBMVSCSI host bus adapter is used which is
SCSI. So when we want some image to appear as a DVD to the guest
(particularly SLOF - our firmware), we use "-device scsi-cd". Or QEMU
extracts this automatically from the "media=cdrom" property of "-drive"
(correct?). And then the SCSI bus tells the guest what is what. SLOF
firmware uses this to create "disk" and "cdrom" aliases to correcly apply
the boot order. So far so good.

Now we are trying (via libvirt) to add both HDD and DVD as "virtio-blk-pci"
devices:

-drive file=virtimg/rhel6-root.img,if=none,format=raw,\
id=drive-virtio-disk1,cache=none \
-device virtio-blk-pci,bus=pci,addr=0x4,\
drive=drive-virtio-disk1,id=virtio-disk1,bootindex=2 \
\
-drive file=virtimg/SLES-11-SP3-DVD-ppc64-GM-DVD1.iso,\
if=none,media=cdrom,id=drive-virtio-disk2,readonly=on,\
format=raw\
-device virtio-blk-pci,bus=pci,addr=0x5,\
drive=drive-virtio-disk2,id=virtio-disk2,bootindex=1

No SCSI bus is created in this case. Both devices appear to SLOF as HDDs so
it creates just one "disk" alias and no "cdrom" alias and if we are not
lucky and DVD got bigger PCI slot#, we will never be able to boot from DVD.

Is there any way to distinguish HDD from DVD via virtio protocol from the
guest (i.e. SLOF)? Thanks!


-- 
Alexey