USB virt status

[harry <harry@hebutterworth.freeserve.co.uk>]

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Here's the latest USB code.

I've spent a few days testing and fixing bugs and it's now possible to
create and mount a filesystem on a USB key in the FE using this code.

I'm in the middle of debugging a problem where dom0 reboots when
flushing a big file to the USB key.  I didn't manage to find a serial
cable for a serial console this evening so I don't have much to go on
yet.

Since last week I've hooked the claim port call into xenbus such that
the configured port is claimed when the device is probed.  At the moment
the code will generate a 7 port virtual USB hub in the FE for each
configured backend device.  It would probably be better to either put
multiple devices on each FE hub or have single port hubs in the front
end.  I think I prefer the latter approach.

The code doesn't currently support hot-reconfiguration of the mapping
between BE usb ports and FE domains but does support hot plug and unplug
of USB devices into configured ports.

I also fixed a few FIXMEs in the code including checking that port
numbering was consistently one-based and checking that URB serialisation
was maintained correctly.

Remaining work:

o - more testing, fix dom0 reboot issue ASAP.
o - reformat to kernel coding style
o - split patch up into manageable chunks for review and patch
submission
o - run the USB code by the usb mailing list
o - fix remaining FIXMEs in code, error codes in particular.
o - more comments and API documentation

If anyone is interested in trying this out the steps are as follows:

Apply the patch to a recent xen-unstable.
make world
Choose to build the usb frontend and backend drivers either as loadable
modules or in kernel (both seem to work equally well).
Do not enable tracing in the xenidc code or the usb FE or BE (there's
too much tracing).
Configure a usb device in a FE domain config script:

usb = ['path=1']

This means attach whatever device is in the BE USB port specified by the
path (i.e. port 1 in this case) to the FE domain. This will create a USB
HUB in the FE domain and whatever device is attached to the BE port will
get attached to port one of the FE hub.

Boot the FE domain.

Load the modules (unless compiled into the kernel).

Plug a USB device in.

You are supposed to be able to load and unload modules and plug/unplug USB
devices however you like but unloading the backend module sometimes hangs
when unregistering a watch.  I think this is likely to be the deadlock in
xenstore that Rusty described.

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