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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jul 05, 2013 at 02:52:08PM +0100, George Dunlap wrote:
> 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. :-)

The high-level goal is that we want to put the network devices with a
network backend and storage devices with storage backend. Ignorning
that for network devices you might want seperate backends for each
device (say one backend for Wireless, one for Ethernet, etc).

Perhaps the logic ought to do grouping - so you say:
 a) "backends:all-network" (which would created one backend with all of the
   wireless, ethernet, etc PCI devices), or
 b) "backends:all-network,seperate-storage", which  create one backend with
  all of the wireless, ethernet in one backend; and one backend domain for each
  storage device?

Naturally the user gets to chose which grouping they would like?
> 
>  -George
> 
> 
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