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

[George Dunlap <george.dunlap@eu.citrix.com>]

On 10/07/13 14:53, Ian Jackson wrote:
> 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.

I think it's a really bad interface decision if a simple typo might 
result in you yanking out your disk.

But in any case, if you think libxl_pci_attach() should automatically 
grab the device, that makes things a lot easier.  I'll write up a patch 
to add a "seize" flag and that will be that.

  -George