Re: [Qemu-devel] [PATCH 4/5] Add generic drive hotplugging

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Aug 24, 2010 at 12:02:30AM +0200, Alexander Graf wrote:
> The monitor command for hotplugging is in i386 specific code. This is just
> plain wrong, as S390 just learned how to do hotplugging too and needs to
> get drives for that.
> 
> So let's add a generic copy to generic code that handles drive_add in a
> way that doesn't have pci dependencies.
> 
> I'm not fully happy with the patch as is. IMHO there should only be a
> single target agnostic drive_hot_add function available. How we could
> potentially fit IF_SCSI in there I don't know though.

I'm not sure that this patch is actually neccessary. Via a undocumented,
sick, dirty hack, you can already use the current drive_add command
without a PCI address, for both virtio + scsi. In fact not using the
PCI address with drive_add is the preferred approach in the new qdev
world even on x86

The key is that you should use  if=none for all cases. Here are two
examples of how libvirt does it currently:

VirtIO:

  drive_add dummy file=/var/lib/libvirt/images/data.img,if=none,id=drive-virtio-disk1,format=raw
  device_add virtio-blk-pci,bus=pci.0,addr=0x0,drive=drive-virtio-disk1,id=virtio-disk1'

SCSI:

  drive_add dummy file=/var/lib/libvirt/images/data.img,if=none,id=drive-scsi0-0-1,format=raw'
  device_add scsi-disk,bus=scsi0.0,scsi-id=1,drive=drive-scsi0-0-1,id=scsi0-0-1

The 'dummy' value there can be absolutely anything you want.
It is totaly ignored when QEMU sees if=none in 2nd arg.

Regards,
Daniel
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