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
--
2.8.0.rc3.226.g39d4020
