Re: udev PATH_ID for virtio devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 27, 2014 at 08:06:15PM +0100, Kay Sievers wrote:
> On Thu, Mar 27, 2014 at 7:59 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Thu, Mar 27, 2014 at 07:43:34PM +0100, Kay Sievers wrote:
> >> On Thu, Mar 27, 2014 at 6:30 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> >>
> >> > If the virtio device is a PCI device, it is really best to
> >> > treat it like you treat any other PCI function (I guess you mean
> >> > function and not device, right? We support multifunction
> >> > devices and some people do pack multiple NICs in a single device)..
> >> >
> >> > At the moment many devices in a single pci function can not happen on a
> >> > PCI system (no multiport) but if we add multiport, we'll follow some
> >> > existing standard to expose this information to the guest.
> >>
> >> This means, that there can currently never multiple devices below one
> >> and the same virtio parent device?
> 
> > There's a single virtio device per pci function (you keep saying
> > device but I hope the distinction is clear and this is
> > just slip of the tongue).
> 
> Right, we talks about sysfs directories and they are called "device",
> we don't really care about the actual bus that is implemented,
> userspace does not really know much about them. :)
> 
> > For net devices under a pci function that is also currently the case,
> > but I can't yet tell you for sure ahead of the time how we'll present
> > multiport devices if we ever implement them.
> >
> > I'm guessing there will be multiple net devices under
> > a single pci device and we'll present a sysfs attribute with the port
> > number in this case.
> >
> > Hmm maybe we should go ahead and add a place-holder
> > attribute so that it's future-proof?
> >
> > I'll write a patch like that and we'll see how it's accepted.
> 
> Netdevs with multiple ports are represented with the standard "dev_id"
> attribute identifying the instance of the driver per parent "device";
> should all work already from the userspace side, if the virtio side
> would use that too.
> 
> Kay

Aha. In that case it's easy - pls assume that if and when we implement
multiple we'll just follow standards and use dev_id.
For virtio pci devices specifically virtio<->pci 1:1 mapping is set
in stone in the spec.

Non pci ones need to be examined separately.