On Thu, Mar 27, 2014 at 9:58 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Thu, Mar 27, 2014 at 09:24:10PM +0100, Tom Gundersen wrote: >> On Thu, Mar 27, 2014 at 8:25 PM, Kay Sievers <k...@vrfy.org> wrote: >> > On Thu, Mar 27, 2014 at 8:13 PM, Michael S. Tsirkin <m...@redhat.com> >> > wrote: >> >> 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 <m...@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 <m...@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. >> > >> > Nice, thanks. That means we can just "jump over" the "virtio*" device >> > (device as in sysfs view), and let the pci parent let identify the >> > device. >> > >> > Background: The logic for device naming generally refuses to touch >> > devices with unknown parent devices in the chain (the directories you >> > see for: ls -l /sys/class/net/), because the parents *could* offer >> > their own bus logic that exposes multiple devices below and we would >> > create clashing names for them. That's why the virt vs. non-virt case >> > needs to be handled explicitly (seems in this case by just skipping >> > it) and it is not necessarily by default the same behaviour. >> >> So Kay and I discussed this a bit more, and found that we likely >> cannot handle virtio nic's nicely. As we would name them based on the >> pci geo, we rely on this being stable between reboots and when >> adding/removing hardware. Is there some way to make this work with >> virtio, or will the 'fake' pci busses simply be enumerated as they are >> created? >> >> Cheers, >> >> Tom > > I think it's standard PCI thing. > Some pci bridges have a slot id register - I'm assuming you > are using these if present? > > If not you'll either need to rely on firmware enumerating buses > consistently, or use the mac of the NIC.
Hi Michael, Sorry to resurrect such an old thread, but this suddenly became relevant again and I see that we never really reached a conclusion. Rereading the discussion it is still not really clear to me what the API promise is, so let me try to rephrase what we need and hopefully you can help me understand where we are at. My understanding is that the enumeration of virtioX buses is global rather than local to the direct parent device of a given bus. That means that we cannot base deterministic naming of child devices (functions) on virtio enumeration, as the names would then depend on the presence or absence of unrelated virtio buses on the system. We have two options that would allow us to get around this: 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 2) if the enumeration of virtio buses was extended with a "port" numebr which was guaranteed to be made local to their direct parent device and moreover be made deterministic. I.e., if there are no virtio sibling buses (but there may be other unrelated virtio buses) the name would always be virtioX.0, and if there are two buses with the same parent their names would always be virtioX.0 and virtioX.1 and always in the same order. Is either of those things something that is already guaranteed or something that could be made working? Cheers, Tom _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
