Re: RFC: Automatically making a PCI device assignable in the config file

[Andrew Cooper <andrew.cooper3@citrix.com>]

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

~Andrew

>
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