[systemd-devel] Utility for persistent alternative driver binding

[Daniel P. Berrange]

On Tue, Dec 08, 2015 at 09:14:17AM -0500, Charles (Chas) Williams wrote:
> On Tue, 2015-12-08 at 11:34 +0200, Panu Matilainen wrote:
> > Hmm, got a pointer? I dont think PCI slots change between reboots 
> > without physically swapping hardware, the "ethX-problem" comes from the 
> > order of device discovery being unstable across boots, which is a 
> > different issue and not relevant for this case.
> 
> With virtual machines the ordering of PCI devices isn't always the same.
> This is especially true with OpenStack which regenerates the
> configurations on the fly.  The only thing that seems to be consistent
> is the MAC address.

The MAC address is not guaranteed to be unique of course - you can have
multiple NICs with the same MAC provided they're connected to different
subnets.

For OpenStack we're working on a feature that allows the user booting
an OpenStack instance to associate an arbitrary tag with each device
they have on their VM. The info about the tags and the currently assigned
device addresses is then exposed to the guest OS via the metadata service
and/or config drive and/or firmware. There will be a utility that can read
this metadata and then register tags against the corresponding devices in
the udev database.

The idea is that people building OpenStack compatible cloud images can
configure their image to look for the device in udev with the desired
user "tag" string. That way they don't need to care about specific
device addresses directly. More info on OpenStack plans is here:

  http://specs.openstack.org/openstack/nova-specs/specs/mitaka/approved/virt-device-role-tagging.html

Regards,
Daniel
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