Re: [Xen-devel] RFC: Automatically making a PCI device assignable in the config file

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

George Dunlap writes ("RFC: Automatically making a PCI device assignable in the 
config file"):
> I've been doing some work to try to make driver domains easier to set
> up and use.  At the moment, in order to pass a device through to a
> guest, you first need to assign it to pciback.  This involves doing
> one of three things:
> * Running xl pci-assignable-add for the device
> * Specifying the device to be grabbed on the dom0 Linux command-line
> * Doing some hackery in /etc/modules.d
>
> None of these are very satisfying.  What I think would be better is if
> there was a way to specify in the guest config file, "If device X is
> not assignable, try to make it assignable".  That way you can have a
> driver domain grab the appropriate device just by running "xl create
> domnet"; and once we have the xendomains script up and running with
> xl, you can simply configure your domnet appropriately, and then put
> it in /etc/xen/auto, to be started automatically on boot.
> 
> My initial idea was to add a parameter to the pci argument in the
> config file; for example:
> 
> pci = ['08:04.1,permissive=1,seize=1']
> 
> The 'seize=1' would indicate that if bdf 08:04.1 is not already
> assignable, that xl should try to make is assignable.

I think it's a design error that this isn't done automatically by
default.

It would be nice if there was a safety check that the device isn't
currently in use by dom0, but I don't think it's essential.  We could
just put a note in the docs saying "if you specify your dom0 nic it
will go away, duh" or something.

And I think this should be done by libxl, under the control of the
usual kinds of xl configuration.

Ian.

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