[RFC] Auto rebind PCI devices

[Mark Williamson <mark.williamson@cl.cam.ac.uk>]

Hi Ryan,

I remember you showing some interest when I suggested rebinding PCI devices 
automatically.  I've hacked together a quick prototype of "what I meant".

I put a bundle at: 
http://www.cambridge.intel-research.net/~mwilli2/pci_auto_rebind.hg

You can fetch my changes into a repository using:
hg unbundle <url>

The behaviour is:
* If the device specified in a domain config file is already bound to another 
driver in dom0, fail creation with an error - as before.
* If the device specified in the config is not currently bound to a driver, 
add it to the pciback driver and create the domain.
* If the device specificed in the config is bound *and* pci-force-rebind is 
set, then unbind it from the existing driver and rebind it to pciback, then 
start the domain.

pci-force-rebind allows users who want total automation in the rebinding 
process to have it, whilst by default preventing the automatic rebinding from 
stealing devices dom0 is relying on.

I'd be interested to see what you think about it - in particular, whether 
there are potential failures in the rebinding code that I ought to be 
catching (e.g. if drivers won't unbind from a device - can that happen?).  
Any objections to the general functionality?

Cheers,
Mark