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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 05/07/13 14:48, Andrew Cooper wrote:
> On 05/07/13 14:45, George Dunlap wrote:
> > On 05/07/13 14:39, Andrew Cooper wrote:
> > > On 05/07/13 12:01, George Dunlap wrote:
> > > > 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.
> > > >
> > > > The problem here is that this would need to be parsed by
> > > > xlu_pci_parse_bdf(), which only takes an argumen tof type
> > > > libxl_device_pci.
> > > >
> > > > Now it seems to me that the right place to do this "seizing" is in xl,
> > > > not inside libxl -- the functions for doing assignment exist already,
> > > > and are simple and straightforward.  But doing it in xl, but as a
> > > > parameter of the "pci" setting, means changing xlu_pci_parse_bdf() to
> > > > pass something else back, which begins to get awkward.
> > > >
> > > > So it seems to me we have a couple of options:
> > > > 1. Create a new argument, "pci_seize" or something like that, which
> > > > would be processed separately from pci
> > > > 2. Change xlu_pci_parse_bdf to take a pointer to an extra struct, for
> > > > arguments directed at xl rather than libxl
> > > > 3. Add "seize" to libxl_device_pci, but have it only used by xl
> > > > 4. Add "seize" to libxl_device_pci, and have libxl do the seizing.
> > > >
> > > > Any preference -- or any other ideas?
> > > >
> > > >    -George
> > > How about a setting in xl.conf of "auto-seize pci devices" ?  That way
> > > the seizing is entirely part of xl
> > Auto-seizing is fairly dangerous; you could easily accidentally yank
> > out the ethernet card, or even the disk that dom0 is using.  I really
> > think it should have to be enabled on a device-by-device basis.
> >
> > I suppose another option would be to be able to set, in xl.conf, a
> > list of auto-seizeable devices.  I don't really like that option as
> > well, though.  I'd rather be able to keep all the configuration in one
> > place.
> >
> >   -George
> Or a slight less extreme version.
>
> If xl sees that it would need seize a device, it could ask "You are
> trying to create a domain with device $FOO.  Would you like to seize it
> from dom0 ?"
That won't work for driver domains, as we want it all to happen 
automatically when the host is booting. :-)
 -George


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