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

[David Vrabel <david.vrabel@citrix.com>]

On 10/07/13 15:48, George Dunlap wrote:
> 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.

I don't think this proposal really helps with avoiding this.  I think
most people will end up always adding 'seize=1' because to avoid having
to do so means altering config files elsewhere and rebooting.

David