olivetalks » usb

USB in Xen – how to make it work

ZoltarStark — Sat, 22 Mar 2008 10:12:42 +0000

In my previous posts I described two approaches for setting up access to USB devices in Xen guest: PCI forwarding and USB forwarding. The results were less than fantastic, I must admit. I’ve been checking different pages on the Internet looking for more advice. Unfortunately it looks like the conclusion is that at this point Xen does not support this feature. Hopefully this will get better in the future.

What can you do now? One suggested approach is to use some kind of USB over IP solution. That does involve spending some money though. USB over IP devices are about €300, a well known example are products from Digi International. Unfortunately I didn’t find any device of this type which would work with Linux clients so this looks like a bad direction to go even if it was cheaper. Another solution mentioned is using a software version of USB over IP. Again, they mostly support Windows clients. I was able to find only one that includes a Linux client – USB Server. At this point it’s in beta so it could be unstable – better test it before you use it on a production system. It includes a kernel driver (released under GPL 2) and binary only programs for the client and the server. It’s not a perfect solution since you still don’t know what’s inside of these binaries.

There are also people working on a similar solution in USB/IP Project. According to them “It is still at a *very* early development stage.” and is not stable.

I’ll try out these options and report here my findings. In the meantime if someone has experiences with any of these two solutions please comment and let us know.

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USB forwarding on Xen – it just does not work

ZoltarStark — Sun, 03 Feb 2008 13:59:41 +0000

In one of my previous posts I was writing about how I setup USB forwarding to a Xen guest by forwarding the whole USB controller. I used PCI pass-through method also known as PCI forwarding. I was able to see the USB controller and the USB device from the Xen guest.

Unfortunately the Xen guest was not stable. It would crash after half an hour, sometimes after two hours. I tried increasing the amount of RAM allocated to the guest, tried both paravirtualized and fully virtualized guests and the result was the same. The guest would crash.

I tried again to use USB forwarding and pass only a single USB device to the guest. After a few more attempts I noticed that I could “partially” forward the USB device itself to a fully virtualized guest (HVM) using this syntax:
usb=1 usbdevice="host:xxxx:yyyy"
The values for xxxx and yyyy are the vendor ID and product ID for the USB device. They can be found out by using the lsusb command. For example on my laptop lsusb produces this output:
Bus 007 Device 001: ID 0000:0000 Bus 005 Device 003: ID 0b97:7772 O2 Micro, Inc. Bus 005 Device 002: ID 0b97:7761 O2 Micro, Inc. Bus 005 Device 001: ID 0000:0000 Bus 004 Device 009: ID 062a:0000 Creative Labs Bus 004 Device 008: ID 413c:2002 Dell Computer Corp. SK-8125 Keyboard Bus 004 Device 007: ID 413c:1002 Dell Computer Corp. Keyboard Hub Bus 004 Device 001: ID 0000:0000 Bus 003 Device 001: ID 0000:0000 Bus 006 Device 001: ID 0000:0000 Bus 002 Device 001: ID 0000:0000 Bus 001 Device 001: ID 0000:0000
So if I wanted to forward the device Dell Computer Corp. SK-8125 Keyboard I’d put the following in the Xen guest configuration file:
usb=1 usbdevice="host:413c:2002"

Ok, so in theory this should have let me see the USB device in Xen guest. Well it did, kind of. One thing I noticed was that I was only able to see some output when running lsusb on the guest when the guest was started from command line using the xm create command. When starting the guest from Virtual Machine Manager GUI I’d see absolutely no USB devices in the guest. Second, even when starting the guest from command line I’d see this kind of output from lsusb:
Bus 001 Device 001: ID 0000:0000
So it looks like something was being forwarded to the guest but it wasn’t the device I wanted to export. It looks like USB pass-through works on Xen only with some USB devices. That matches with what I’ve read at xgu.ru.

The final result – at the moment I’m using the USB device from the physical host. At least until I have time to look at it again.

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USB forwarding on Xen

ZoltarStark — Thu, 24 Jan 2008 22:00:11 +0000

Recently I was setting up a Xen guest which needed access to a USB port on a CentOS 5.1 host. I searched the Internet for instructions on how to use USB forwarding or USB pass-through but I was not able to find anything which would work on the Xen 3.0.3 I’m using. I decided to set up PCI pass-through instead.

To set it up, I followed instructions written by Jón Fairbairn at xensource.com. The pciback module in the CentOS 5.1 kernel doesn’t support the hide parameter so I left that out from my setup. It doesn’t seem to be necessary, anyway, for the driver for the USB controller in the host can be unbound from the PCI slot used by the controller.

To make sure the PCI slot is exported to Xen guests when the host system boots I created a xenpciexport script and placed it in the /etc/init.d/ directory. You can download the code from here xenpciexport.txt

The script xenpciexport is set up to start before xend and xendomains to make sure the PCI forwarding is working before any guest is running. It stops after xend and xendomains. That’s controlled by the line:

# chkconfig: 2345 97 02

you can see in the script header.

After copying the file to /etc/init.d you need to run

chkconfig --add xenpciexport

to create the appropriate links in the /etc/rc*.d/ directories.

To find out the slot number for the USB controller use lspci and lsusb commands. If the script is set up correctly you can plug in the USB device and run

service xenpciexport stop

After that the results of lsusb should include the USB device you want to export. Then run

service xenpciexport start

and now lsusb won’t show this device anymore – it’s hidden from the host and visible to Xen guests.

Before you start the Xen guest which is supposed to have access to the exported device add this line to its configuration file:

pci = [ '0000:00:1d.1' ]

The number in quotes must be the same as the SLOT variable in the xenpciexport script.

After that you need to patch your Xen installation. The version installed in CentOS 5.1 contains a bug which makes it impossible to use PCI pass-through. The fix can be found at CentOS Bug Tracker. Make sure you also fix the file pciif.py as specified in the note. In total there are three files which need to be edited: iopif.py, irqif.py and pciif.py.

Now you can finally start the Xen guest. When it finishes booting log into it and run lsusb there to confirm that the device is visible to the guest. lspci in the guest should also show you the USB controller. It is important to run the xenpciexport script before you start your guest, otherwise the USB device will not be visible to the guest OS.

The Xen guest has now full access to the USB device.

Here you can read more about PCI passthrough on Xen.

Update:
It turns out that this setup was causing the Xen guest to crash. You can read more in a new post.

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olivetalks » usb

USB in Xen – how to make it work

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