From: Ido Schimmel <ido...@mellanox.com>
Date: Sun, 11 Mar 2018 09:44:39 +0200
> Petr says:
> mlxsw_spectrum supports offloading of a tc action mirred egress mirror
> to a gretap or ip6gretap netdevice, which necessitates calls to
> functions defined in ip_gre, ip6_gre and ip6_tunnel modules. Previously
> this was enabled by introducing a hard dependency of MLXSW_SPECTRUM on
> NET_IPGRE and IPV6_GRE. However the rest of mlxsw is careful about
> picking which modules are absolutely required, and therefore the better
> approach is to make mlxsw_spectrum tolerant of absence of one or both of
> the GRE flavors.
> One way this might be resolved is by keeping the code in mlxsw_spectrum
> intact, and defining defaults for functions that mlxsw_spectrum depends
> on. The downsides are that other modules end up littered with these
> do-nothing defaults; that the driver ends up carrying quite a bit of
> dead code; and that the driver ends up having to explicitly depend on
> IPV6_TUNNEL to prevent configurations where mlxsw_spectrum is compiled
> in and and ip6_tunnel is a module, something that it currently can treat
> as an implementation detail of the IPV6_GRE dependency.
> Alternatively, the driver should just bite the bullet and ifdef-out the
> code that handles configurations that are not supported. Since that's
> what we are doing for IPv6 dependency, let's do the same for the GRE
> Patch #1 introduces a wrapper function for determining the value of
> ipv6.sysctl.multipath_hash_policy, which defaults to 0 on non-IPv6
> builds. That function is then used from spectrum_router.c, instead of
> the direct variable reference that was introduced there during the short
> window when the Spectrum driver had a hard dependency on IPv6.
> Patch #2 moves one function to keep together in one block all the
> callbacks for handling (IPv4) gretap mirroring.
> Patch #3 then introduces the ifdefs to hide the irrelevant code.