udev PATH_ID for virtio devices

[Kay Sievers]

On Tue, Aug 25, 2015 at 1:52 PM, Michael S. Tsirkin <mst at redhat.com> wrote:
> On Tue, Aug 25, 2015 at 01:46:49PM +0200, Kay Sievers wrote:
>> On Tue, Aug 25, 2015 at 1:43 PM, Michael S. Tsirkin <mst at redhat.com> wrote:
>> > On Mon, Aug 24, 2015 at 06:10:01PM +0200, Tom Gundersen wrote:

>> >> 1) if there is a guarantee now and in the future (even if only
>> >> restricted to netdevs) that no virtio bus will have a direct sibling
>> >> bus (i.e., with the same parent device); or
>> >
>> > I think this is the case. The virtio bus is an artifact.
>> > There's always a single one behind each pci device.
>> > Is this sufficient?
>>
>> I *think* is not good enough for udev to offer such functionality.
>>
>> We need an authoritative answer that this cannot happen with today's
>> code, and also that there are no plans to ever make multiple virtio
>> devices per parent device.

> But if virtio will make such a promise, will that be sufficient?

Sure. I mean we need to be reasonable sure, that there will never
be more than one virtio device per parent device. Otherwise an
innocent looking kernel change will just break existing userspace
setups which made assumptions which would then not be true anymore.

Kay