Re: Can't access USBs from DomU

[Dave Hill <davehill@xxxxxxxxx>]

On 2020-07-01 1:32 a.m., Martin Hargreaves wrote:

Thank you for responding, David.

Yes, I have been using the link you recommended in order to gain access to the USBs. It appears on Dom0 to have worked okay but I simply can't 'see' the USB on my para-virtualization VM. Thank you for the  www.spice-space.org link; I'll look into that.

   Martin..

On 2020-06-25 8:56 a.m., hargreaves martin wrote:

A very quick question (hopefully).

On Dom0, I can attach my USBs.

$ sudo xl usbdev-attach ubud1 hostbus=2 hostaddr=36

$ sudo xl usb-list 5

Devid Type BE state usb-ver ports

0 qusb 0 1 2 8

Port 1: Bus 002 Device 025

Port 2: Bus 002 Device 024

Port 3:

…

But I can’t see them in my DomU (Ubuntu). Any suggestions?

Any help would be very much appreciated.

Martin..

I don't do it that way anymore (I use SPICE instead), but the Xen USB Passthrough page helped me when I was trying to figure out how to do it the way you are now: https://wiki.xenproject.org/wiki/Xen_USB_Passthrough

Regards,

David

Hi Martin,

Sorry - I should have mentioned that, AFAIK, SPICE is only for use with hvm domUs, which all of mine are. 

I found the Spice documentation a bit hard to dig through (Spice for Newbies felt like a Masters-level course :-).

In case it might save you some time and effort, FWIW, here is my understanding of Spice basics .

Spice has three pieces - a Spice server, one or more guest domUs running the spice agent software, and one or more sessions of a Spice viewer/client. They interact using the Spice protocol.

SERVER
Recent releases of major Linux distributions already have the server component, libspice, available. I  run my dom0 on Debian 10 and run the Spice server there. I didn't have to do anything special to get the Spice server running. (It could be I installed one or more of the libspice-server packages using the package manager). What I mean is that I didn't have to build an upstream version of qemu as I thought I might after reading the (very helpful) Xen page about Spice:
https://wiki.xenproject.org/wiki/SPICE_support_in_Xen

GUESTS
Linux
I add
pci=nomsi
to the kernel boot line as recommended on the Xen page.

When first creating a Linux domU, I connect via vnc to check for the spice agent software, vdagent, and install it if it's not already in.

I use the Spice section of sample xl configuration file from the Xen page as well - it works fine for me.  Some of the other configuration choices there don't work for me so I modify other parts of the sample file.

I believe it's still true that qxl doesn't work for Linux-based domUs, so in the domU .cfg files I have:
#VIDEO
videoram                = 128
vga                     = 'stdvga'

Windows
For a Windows domU, the vdagent software is available from the Windows binaries subsection of the Guest section on the spice-space download page:
https://www.spice-space.org/download.html

The page says:
This installer contains some optional drivers and services that can be installed in Windows guest to improve SPICE performance and integration. This includes the qxl video driver and the SPICE guest agent (for copy and paste, automatic resolution switching, ...)

I'm not sure how the options are accessed or configured - there doesn't seem to be a Spice-tools executable. I don't have the qxl component working at this point - just haven't had the motivation to look for it as I use the Windows domU infrequently - so I have
vga                     = 'stdvga'
in the Windows .cfg file as well.

I use a modified version of the sample xl.cfg lines from the Xen page for Windows too.  I note that I had to change viridian= from 1 to 0. With viridian=1, my Windows 10 machine wouldn't boot.

VIEWER/CLIENT
Finally, the viewer software (the actual magic in all of this) is available from the Spice downloads page as well, and (at least on Debian) from the distribution package manager. As you may already have seen, there are several options here. I use virt-viewer because it suits my needs - haven't tried the others. I find it a little unstable - the viewer has some problem with mouse clicks that seems to cause it to shut down from time to time.

One handy feature of virt-viewer is that it will also connect via vnc protocol, by replacing:
spice://192,168.x.x:6000 (or whathaveyou)
with:
vnc://192,168.x.x:6000

Once I have all of the above, it's simple to redirect a USB device to a domU through the File menu of virt-viewer, so long as there is some number of ports set out for redirect in the xl.cfg file, like:
spiceusbredirection=4

I hope you haven't independently discovered all of this already, but, if you have, I'd appreciate hearing of any errors in the above, as it's been a while since I actually went through it.

Regards,

David