Re: [Qemu-devel] [QEMU question] Disk hot plugging without working PCI hotplug - possible?

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 06/07/2013 12:29 AM, Frederic Konrad wrote:
> On 06/06/2013 15:59, Alexey Kardashevskiy wrote:
>> On 06.06.2013 22:44, Frederic Konrad wrote:
>>> On 06/06/2013 12:13, Alexey Kardashevskiy wrote:
>>>> Hi!
>>>>
>>>> For the pseries platform (server PPC64) we do not support PCI hotplug
>>>> yet.
>>>> However we still want to hot plug disks.
>>>>
>>>> As a workaround, we could add multiple SCSI host devices
>>>> (virtio-scsi-pci,
>>>> spapr-vscsi) without any disk attached and later (using qemu console)
>>>> attach drives to them as we do with the "-drive" parameter in the
>>>> command line.
>>>>
>>>> So I enabled CONFIG_PCI_HOTPLUG_OLD=y and tried.
>>>>
>>>> However, drive_add console command works only with PCI what eliminates
>>>> "spapr-vscsi" from the list. Oookay.
>>>>
>>>> Then I tried running qemu with "-device virtio-scsi-pci,id=device0" and
>>>> later doing "drive_add 0 file=virtimg/test1" from the qemu console. This
>>>> time qemu responded with "Device is not a SCSI adapter" what is
>>>> correct as
>>>> nowadays virtio-XXXX-pci devices are not what are they called as they
>>>> simply create underlying virtio-bus, attach a real virtio-XXXX-device
>>>> there
>>>> (which is not PCI) and only then attach disk to non-PCI virtio device.
>>> Hi,
>>>
>>> Seems it's a bug: il should be compatible with the old virtio-scsi-pci.
>>> What's the meaning of the "0" in drive_add command?
>> It is a PCI slot number, the complete address would include a domain and
>> a bus.
>>
>>
> 
> Ok thanks, I'll take a look.
>>> Fred
>>>> So as I see there is no way to attach a disk to an existing controller in
>>>> already running qemu.
>>>>
>>>> This is how I add disks to qemu now:
>>>>    -device virtio-scsi-pci,id=virtioscsi0 \
>>>>    -drive file=virtimg/fc18guest,if=none,id=drive0,readonly=off,
>>>> format=raw,media=disk,werror=stop,rerror=stop \
>>>>    -device scsi-disk,id=scsidisk0,bus=virtioscsi0.0,channel=0,
>>>> scsi-id=0,lun=0,drive=drive0,removable=off \
> 
> This two last command isn't available in the monitor?
>>>>
>>>> I want to only add "-device virtio-scsi-pci,id=virtioscsi0" to the
>>>> command
>>>> line and do the rest from the qemu console.
>>>>
>>>> Am I missing some useful command from qemu console or anything else?
>>>> Thanks!

This works (thanks to Anthony):

./qemu-system-ppc64 \
 -L "qemu-ppc64-bios/" \
 -nodefaults \
 -chardev "stdio,id=char1,signal=off,mux=on" \
 -device "spapr-vty,id=ser1,chardev=char1" \
 -mon "chardev=char1,mode=readline,id=mon1" \
 -m "1024" \
 -machine "pseries" \
 -nographic \
 -vga "none" \
 -enable-kvm \
 -kernel "guest.vmlinux.n" \
 -initrd "1.cpio" \
 -device "virtio-scsi-pci,id=foo"

And then issue 2 commands in the qemu console:

 drive_add auto file=virtimg/fc18guest,if=none,id=bar
 device_add scsi-disk,bus=foo.0,drive=bar,unit=0

The guest is even able to autodetect new volume. Profit.


-- 
Alexey