Re: [RFC PATCH net-next 2/3] seg6: add SRv6 L2 tunnel device (srl2)

[Andrea Mayer]

On Thu, 26 Mar 2026 17:44:29 +0100
Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> wrote:

> 
> 

Thanks Nicolas for your time and for the review.


> Le 22/03/2026 à 01:05, Andrea Mayer a écrit :
> > Introduce srl2, an Ethernet pseudowire device over SRv6. It
> > encapsulates L2 frames in IPv6 with a Segment Routing Header for
> > transmission across an SRv6 network.
> > 
> > The encapsulation logic reuses seg6_do_srh_encap() with
> > IPPROTO_ETHERNET. The transmit path uses the standard IPv6 tunnel
> > infrastructure (dst_cache, ip6_route_output, ip6tunnel_xmit).
> > 
> > The device is configured with a segment list for point-to-point
> > L2 encapsulation.
> > 
> > Usage:
> > 
> >   ip link add srl2-0 type srl2 segs fc00::a,fc00::b
> > 
> > Co-developed-by: Stefano Salsano <stefano.salsano@xxxxxxxxxxx>
> > Signed-off-by: Stefano Salsano <stefano.salsano@xxxxxxxxxxx>
> > Signed-off-by: Andrea Mayer <andrea.mayer@xxxxxxxxxxx>
> > ---
> >  include/linux/srl2.h      |   7 +
> >  include/uapi/linux/srl2.h |  20 +++
> >  net/ipv6/Kconfig          |  16 +++
> >  net/ipv6/Makefile         |   1 +
> >  net/ipv6/seg6.c           |   1 +
> >  net/ipv6/srl2.c           | 269 ++++++++++++++++++++++++++++++++++++++
> >  6 files changed, 314 insertions(+)
> >  create mode 100644 include/linux/srl2.h
> >  create mode 100644 include/uapi/linux/srl2.h
> >  create mode 100644 net/ipv6/srl2.c
> > 
> > diff --git a/include/linux/srl2.h b/include/linux/srl2.h
> > new file mode 100644
> > index 000000000000..c1342b979402
> > --- /dev/null
> > +++ b/include/linux/srl2.h
> > @@ -0,0 +1,7 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +#ifndef _LINUX_SRL2_H
> > +#define _LINUX_SRL2_H
> > +
> > +#include <uapi/linux/srl2.h>
> > +
> > +#endif
> Is this really needed?

No. Moving IFLA_SRL2_* to if_link.h makes both srl2.h headers
unnecessary.


> 
> > diff --git a/include/uapi/linux/srl2.h b/include/uapi/linux/srl2.h
> > new file mode 100644
> > index 000000000000..e7c8f6fc0791
> > --- /dev/null
> > +++ b/include/uapi/linux/srl2.h
> > @@ -0,0 +1,20 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
> > +/*
> > + *  SRv6 L2 tunnel device
> > + *
> > + *  Author:
> > + *  Andrea Mayer <andrea.mayer@xxxxxxxxxxx>
> > + */
> > +
> > +#ifndef _UAPI_LINUX_SRL2_H
> > +#define _UAPI_LINUX_SRL2_H
> > +
> > +enum {
> > +	IFLA_SRL2_UNSPEC,
> > +	IFLA_SRL2_SRH,	/* binary: struct ipv6_sr_hdr + segments */
> > +	__IFLA_SRL2_MAX,
> > +};
> > +
> > +#define IFLA_SRL2_MAX (__IFLA_SRL2_MAX - 1)
> It should probably be generated automatically from specs, see
> https://docs.kernel.org/userspace-api/netlink/intro-specs.html
> 

We'll add srl2 to rt-link.yaml. It seems that if_link.h is not
auto-generated from the spec yet, so I think we need to add
IFLA_SRL2_* there manually like the other link types.


> > [snip]
> > +static void srl2_setup(struct net_device *dev)
> > +{
> > +	ether_setup(dev);
> > +
> > +	dev->netdev_ops = &srl2_netdev_ops;
> > +	dev->needs_free_netdev = true;
> > +	dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS;
> > +	dev->needed_headroom = LL_MAX_HEADER + sizeof(struct ipv6hdr) +
> > +			       SRL2_SRH_HEADROOM_EST;
> > +
> > +	dev->priv_flags &= ~IFF_TX_SKB_SHARING;
> > +	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
> > +	dev->lltx = true;
> > +
> Maybe setting dev->netns_immutable to true ?
> 

It makes sense; the SRv6 configuration is bound to the current
netns, so the device should stay there as well.


> Regards,
> Nicolas

Thanks,
Andrea