On 20.02.2017 17:00, Cornelia Huck wrote: > On Mon, 20 Feb 2017 15:34:49 +0100 > Viktor Mihajlovski <mihajlov@xxxxxxxxxxxxxxxxxx> wrote: > >> Hi, >> >> with systemd > v229 all virtio block devices will receive persistent >> device names in the format /dev/disk-by/virtio-pci-<busid>, the >> last component being the udev built-in path_id. >> >> This naming introduces some issues. >> >> First and obvious, there are virtio implementations not based >> on PCI, like virtio-ccw (currently only on s390) and virtio-mmio >> (for which I can't speak). This results in persistent names like >> /dev/disk-by/virtio-pci-0.0.0001, where the bus id is a CCW id. >> One seemingly obvious remedy would be to make the path_id return >> virtio-ccw-<busid> or more generally virtio-<subsystem>-<busid>, >> both easily done with small patches to systemd-udev. >> >> But then, I find this naming scheme somewhat weird. >> A virtio disk shows up as a regular PCI function on the PCI >> bus side by side with other (non-virtio) devices. The naming otoh >> suggests that virtio-pci is a subsystem of its own, which is simply >> incorrect from a by-path perspective. > > From the ccw perspective, this is quite similar: The virtio proxy > device shows up on the ccw bus, just like e.g. a dasd device shows up > on the ccw bus. > >> >> Using just the plain PCI path id is actually sufficient to identify >> a virtio disk by its path. This would be in line with virtio >> network interface path names which use the plain PCI naming. > > Same for ccw: The id on the ccw bus (devno) is already unique and > persistent. > >> >> One could argue about back-level compatibility, but virtio by-path >> naming has changed multiple times. We have seen virtio-pci-virtio<n> >> (not predictable), pci-<busid> and virtio-pci-<busid> already. It >> might be a good time now to settle on a common approach for all >> virtio types. >> >> For the reasons above, I'd vote for <subsystem>-<busid>, which >> would work for PCI and CCW, not sure about ARM MMIO though. >> Opinions? > > I'm not sure whether there is any reason to make virtio special, > although this depends upon what virtio-mmio looks like in the Linux > device model (any arm folks here?) > > In the end, I'd be happy with any naming scheme that does not include > 'pci' for non-pci devices. > Michal, as author of commit f073b1b3c0f4f0df1b0bd61042ce85fb5d27d407 that introduced this behavior: can you comment on the reasoning for prepending virtio- to the bus, i.e. why would pci-<busid> not sufficiently identify the device? -- Mit freundlichen Grüßen/Kind Regards Viktor Mihajlovski IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Martina Köderitz Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen Registergericht: Amtsgericht Stuttgart, HRB 243294 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
