[systemd-devel] [PATCH] udev rules: add udev rule to create /dev/ptp_kvm

[Lennart Poettering]

On Tue, 28.02.17 16:54, Daniel P. Berrange (berrange at redhat.com) wrote:

> On Mon, Feb 27, 2017 at 11:50:59PM -0300, Marcelo Tosatti wrote:
> > On Sun, Feb 26, 2017 at 09:52:18PM +0100, Lennart Poettering wrote:
> > > On Thu, 23.02.17 22:20, Marcelo Tosatti (mtosatti at redhat.com) wrote:
> > > 
> > > > 
> > > > Its necessary to specify the KVM PTP device name in userspace.
> > > > 
> > > > In case a network card with PTP device is assigned to the guest,
> > > > it might be the case that KVM PTP gets /dev/ptp0 instead of /dev/ptp1. 
> > > > 
> > > > Fix a device name for the KVM PTP device.
> > > 
> > > What's the symlink precisely good for, can you elaborate? 
> > 
> > You want to configure Chrony to use PTP in the guest to sync with the
> > host.
> > 
> > You need to add a entry to /etc/chrony.conf pointing to "/dev/ptp0", 
> > the ptp_kvm device.
> > 
> > However, it might be the case that a PCI assigned device has a PTP
> > clock, and it can be registered as "/dev/ptp0" and ptp_kvm as
> > "/dev/ptp1".
> > 
> > > Also, what's the benefit of shipping this upstream? Why not ship that
> > > rule with kvm?
> > 
> > qemu-kvm package? Sure i can do that, but then all distributions 
> > have to do the same with their own packages.
> 
> qemu-kvm is installed in the host OS only, but this rule needs to be
> set in the guest OS, unless you want to bundle it in with qemu-guest-agent
> RPM, but that's not really a directly related package, so we'd liekly have
> to create a new package for this and try and get distros to ensure it is
> installed in all guest OS. We've had qemu-guest-agent for years now and
> we've still not got all distros installing it. So not shipping this kind
> of rule with udev means that it'll almost certainly end up being missing
> in the majority of guest installs for many years to come.

Thank you for the explanation. This was what I was looking for.

I generated a github PR now from this:

https://github.com/systemd/systemd/pull/5495

Marcelo, it's generally preferable these days to submit via github PRs
right-away.

Let's continue discussion on the github PR. Thanks.

Lennart

-- 
Lennart Poettering, Red Hat