Re: [Qemu-devel] [libvirt] [PATCH 3/5] qemu: add usb-bot support from disks points of view

[Guannan Ren <gren@redhat.com>]

On 09/02/2013 08:57 PM, Daniel P. Berrange wrote:
> On Mon, Sep 02, 2013 at 05:38:42PM +0800, Guannan Ren wrote:
>> usb-bot only supports 16 luns(0~15) and they must be contiguous,
>> (using lun 0 and 2 without 1 doesn't work). In this case qemu
>> doesn't throw an error, we can not find the lun 2 in guests. So
>> Adding a checking function in libvirt to prevent from this case.
> Hmm, this seems like a problematic restriction.
>
> How does this work if we start off a guest with 3 disks
> attached to the usb-bot SCSI controller. Then hot-unplug
> the 2nd disk.

Currently, the qemu will throw out an error when I hot-unplug any of 
disks attached to usb-bot controller.

{ "execute": "device_del", "arguments": { "id": "scsi1-0-0-1"}}
{"error": {"class": "GenericError", "desc": "Bus 'scsi1.0' does not 
support hotplugging"}}

Libvirt will report an error:
# virsh detach-disk rhel64qcow2 sdd --current
error: Failed to detach disk
error: internal error: unable to execute QEMU command 'device_del': Bus 
'scsi1.0' does not support hotplugging



> Next time we need will need to start with with LUNs 0
> and 2 populated only, otherwise we have ABI change upon
> migrate or save/restore.
>
> I think this restriction about contiguous luns must be
> removed if this device is to be usable with multiple luns.
>
> Daniel