[systemd-devel] RTNETLINK support for tuntap devices in systemd-networkd

Tom Gundersen teg at jklm.no
Mon Mar 23 15:05:11 PDT 2015

Hi Louis,

On Sun, Mar 22, 2015 at 3:02 PM, Louis Feuvrier <louis at feuvrier.org> wrote:
> I have been watching the recording[1] of Tom Gundersen's talk at
> FOSDEM15 and around 13:45 he talks about integrating RTNETLINK support
> for tuntap devices. I wanted to know if this feature is still of
> interest to you guys working on systemd-networkd.

Yes, very much so!

> I am also wondering how a continuous integration might work out: the
> kernel mainline would probably support both ioctls and rtnetlink APIs.
> Would this also be the case for systemd-networkd, as a means to support
> older kernels?

We do not support old kernels indefinitely in systemd, so we would be
able to transition to a new API and drop the old one eventually.

> The folks at iproute2 seemed to think supporting both APIs was redundant
> and not interesting[2]. However, I feel like evolution of the APIs
> cannot be done any other way with backward compatibility.

I fully agree with Stephen's reasoning in that discussion. It is a
shame they didn't follow through with that. If anyone were to have
another stab at getting a rtnl interface for tun/tap into the kernel
that would be really great.

The current ioctl interface is really ugly in my opinion and having a
consistent API and feature-set with the rest of the netdev types would
make a lot more sense to me. It would give us things like not needing
access to /dev/net from networkd, or being able to provide the correct
MAC address when creating a device, rather than having to set that in
several steps, and of course it would also allow us to (eventually)
drop/simplify a lot of code from networkd.

Thanks for your interest!



> [1] http://video.fosdem.org/2015/
> [2] http://patchwork.ozlabs.org/patch/26839/

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