----- Original Message ----- From: "Daniel P. Berrange" <berrange@redhat.com> To: "Guannan Ren" <gren@redhat.com> Cc: libvir-list@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