On 04.11.2016 22:51, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <m...@google.com>
>
> Routes can specify an mtu explicitly or inherit the mtu from
> the underlying device - this inheritance is implemented in
> dst->ops->mtu handlers ip6_mtu() and ip6_blackhole_mtu().
>
> Currently changing the mtu of a device adds mtu explicitly
> to routes using that device.
>
> ie.
> # ip link set dev lo mtu 65536
> # ip -6 route add local 2000::1 dev lo
> # ip -6 route get 2000::1
> local 2000::1 dev lo table local src ... metric 1024 pref medium
>
> # ip link set dev lo mtu 65535
> # ip -6 route get 2000::1
> local 2000::1 dev lo table local src ... metric 1024 mtu 65535 pref
> medium
>
> # ip link set dev lo mtu 65536
> # ip -6 route get 2000::1
> local 2000::1 dev lo table local src ... metric 1024 mtu 65536 pref
> medium
>
> # ip -6 route del local 2000::1
>
> After this patch the route entry no longer changes unless it already has an
> mtu.
> There is no need: this inheritance is already done in ip6_mtu()
>
> # ip link set dev lo mtu 65536
> # ip -6 route add local 2000::1 dev lo
> # ip -6 route add local 2000::2 dev lo mtu 2000
> # ip -6 route get 2000::1; ip -6 route get 2000::2
> local 2000::1 dev lo table local src ... metric 1024 pref medium
> local 2000::2 dev lo table local src ... metric 1024 mtu 2000 pref
> medium
>
> # ip link set dev lo mtu 65535
> # ip -6 route get 2000::1; ip -6 route get 2000::2
> local 2000::1 dev lo table local src ... metric 1024 pref medium
> local 2000::2 dev lo table local src ... metric 1024 mtu 2000 pref
> medium
>
> # ip link set dev lo mtu 1501
> # ip -6 route get 2000::1; ip -6 route get 2000::2
> local 2000::1 dev lo table local src ... metric 1024 pref medium
> local 2000::2 dev lo table local src ... metric 1024 mtu 1501 pref
> medium
>
> # ip link set dev lo mtu 65536
> # ip -6 route get 2000::1; ip -6 route get 2000::2
> local 2000::1 dev lo table local src ... metric 1024 pref medium
> local 2000::2 dev lo table local src ... metric 1024 mtu 65536 pref
> medium
>
> # ip -6 route del local 2000::1
> # ip -6 route del local 2000::2
>
> This is desirable because changing device mtu and then resetting it
> to the previous value shouldn't change the user visible routing table.
>
> Signed-off-by: Maciej Żenczykowski <m...@google.com>
> CC: Eric Dumazet <eduma...@google.com>
> ---
> net/ipv6/route.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 947ed1ded026..fa90d14302f7 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -2758,6 +2758,7 @@ static int rt6_mtu_change_route(struct rt6_info *rt,
> void *p_arg)
> PMTU discouvery.
> */
> if (rt->dst.dev == arg->dev &&
> + dst_metric_raw(&rt->dst, RTAX_MTU) &&
> !dst_metric_locked(&rt->dst, RTAX_MTU)) {
> if (rt->rt6i_flags & RTF_CACHE) {
> /* For RTF_CACHE with rt6i_pmtu == 0
>
Yep, that makes sense.
Acked-by: Hannes Frederic Sowa <han...@stressinduktion.org>
