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

[Daniel P. Berrange]

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.

Regards,
Daniel
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