[libvirt] how to know if PCI device has SR-IOV PF capability

[Moshe Levi]

Hi Laine,

Did you have a bug for this issue? 
I need it to document it in for my workaround in OpenStack. 
Thanks,
	Moshe Levi. 

> -----Original Message-----
> From: Daniel P. Berrange [mailto:berrange at redhat.com]
> Sent: Monday, November 23, 2015 6:29 PM
> To: Laine Stump <laine at laine.org>
> Cc: libvir-list at redhat.com; Moshe Levi <moshele at mellanox.com>
> Subject: Re: [libvirt] how to know if PCI device has SR-IOV PF capability
> 
> On Mon, Nov 23, 2015 at 11:26:11AM -0500, Laine Stump wrote:
> > On 11/23/2015 10:40 AM, Daniel P. Berrange wrote:
> > >On Mon, Nov 23, 2015 at 10:34:43AM -0500, Laine Stump wrote:
> > >
> > >>If we're going to switch to emiting virt_functions whenever a device
> > >>has the potential to provide VFs, we may as well make it worthwhile
> > >>and also emit the maximum possible VFs for the device, maybe simply:
> > >>
> > >>     <capability type='virt_functions' maxCount='7'>
> > >>
> > >>(the current count is implicit in the number of entries in the list
> > >>that follows. I don't have an opinion on whether it is better to
> > >>also include explicitly with, e.g. "count='7'", or just leave it implicit).
> > >Is there any way for us to actually discover the max count ? If so,
> > >then it seems nice to include it.
> >
> > Yes. I don't know if it existed back when that code was originally
> > added, but at least RHEL6.7 (the oldest OS I have running on a machine
> > with an SRIOV-capable card) and later have two files in the device's
> > sysfs, sriov_numvfs and sriov_totalvfs. The former is the number that
> > are currently active, and the latter is the maximum possible for this PF.
> >
> > (On a related topic - you can change the number of currently active
> > VFs by writing "0" to sriov_numvfs then writing the desired number to
> > it; this does temporarily delete any VFs that are already active
> > though, so it can only be done if none are in use. I've planned to
> > hook libvirt networks up to this so that VFs can be enabled completely
> > within libvirt (since the driver commandline method isn't consistent
> > between different vendors, and I believe is now considered to be
> > deprecated). Since Openstack doesn't use libvirt networks but may want
> > similar functionality, I'm wondering where would be a good place to do
> > that. We could provide something via the node-device API, but that
> > couldn't be automatically done by libvirtd at startup; alternately
> > Openstack could create a network but not use it, but that just seems
> > conceptually confusing even though it would work.)
> 
> There is scope to extend node device APIs to allow definition of persistent
> config for virtual devices. We have similar scenario wrt NPIV devices which are
> dynamically allocatable
> 
> Regards,
> Daniel
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