Re: [libvirt] [PATCH 0/5]qemu: add usb-bot scsi controller support
----- Original Message -----
From: "Daniel P. Berrange" <berrange(a)redhat.com>
To: "Guannan Ren" <gren(a)redhat.com>
Cc: libvir-list(a)redhat.com
Sent: Tuesday, September 3, 2013 5:38:08 AM
Subject: Re: [libvirt] [PATCH 0/5]qemu: add usb-bot scsi controller support
On Mon, Sep 02, 2013 at 05:38:39PM +0800, Guannan Ren wrote:
>
> BZ:https://bugzilla.redhat.com/show_bug.cgi?id=917702
> qemu patch:http://lists.gnu.org/archive/html/qemu-devel/2013-01/msg02200.html
>
> These patch aims to add usb-bot SCSI controller support for libvirt.
> As usb-storage libvirt already supported, usb-bot only supports one
> SCSI target with SCSI ID 0.
> The difference is that usb-storage creates SCSI HBA and additionaly
> either a scsi-disk or a scsi-generic device, usb-bot only creates the
> SCSI HBA. we can attach a SCSI device to it with another -device.
>
> usb-bot supports a single target and a number of luns. The limit is
> 15 luns (0~15 LUN ID) and they must be contiguous(using lun 0 and 2
> without 1 doesn't work).
>
> Athought usb-bot is a SCSI controller it needs to be attached to a
> exsiting USB controller for work. So it has to use address of usb type.
>
> Libvirt XML:
>
> <devices>
> ...
> <disk type='file' device='disk'>
> <driver name='qemu' type='raw'/>
> <source file='/var/lib/libvirt/images/disk.qcow2'/>
> <target dev='sdc' bus='scsi'/>
> <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
> </disk>
> <controller type='usb' index='0'/>
> <controller type='scsi' index='0' model='usb-bot'>
> <address type='usb' bus='0' port='1'/>
> </controller>
> ...
> </devices>
How does this work from a hotplug POV. With usb-storage you could
just hotplug the <disk> device. Now it seems we need two separate
hotplug calls one of the <controller> and one for the <disk> and
the reverse.
Yes, I will think about the hotplug.
>
> The QEMU commandline:
>
> qemu ${other_vm_args} \
> -device piix3-usb-uhci,id=usb \
> -device usb-bot,id=scsi0,bus=usb.0,port=1 \
> -drive
file=/var/lib/libvirt/images/disk.qcow2,if=none,id=drive-scsi0-0-0-0,format=raw \
> -device
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0
>
> As the usb-storage creates scsi disk automatically which doesn't let
> you set scsi-disk properties such as vendor, product, wwn, channel,
> scsi-id and lun. So QEMU guys prefer usb-bot to usb-storage.
> So this is the first part of the whole work. Next step will replace
> usb-storage with usb-bot when disk in xml uses usb bus like
> <disk ...>
> <...>
> <target bus='usb'>
> </disk>
I'm not really a fan of introducing 2 different ways to
configure
the exact same device.
The idea is to use usb-bot instead of usb-storage in this case if usb-bot capability is
available.
usb-storage automatically expands into two devices, a SCSI controller and a SCSI device.
And user
cannot set any property values to this SCSI device such as vendor, product, wwn, channel,
scsi-id
and lun. usb-bot gives the more flexible configurations.
I think it is to use usb-bot if usb-bot is supported, otherwise still use usb-storage. The
xml
will not change at all.
Guannan