From 39bfa1615fd1cafe5df6d8fc9d34528e8d3906e2 Mon Sep 17 00:00:00 2001
From: Pim van Pelt <pim@ipng.nl>
Date: Fri, 13 Aug 2021 15:02:31 +0200
Subject: [PATCH] Add sync of VPP mtu changes into Linux interfaces

This is a straight foward copy of the VPP L3 (packet) MTU into the Linux
host interface, for any change on an interface/sub-int for which a LIP is
defined.

As with Linux itself, no care is taken to ensure that the parent interface
(e0) has a higher MTU than the child interface (e0.10).

DBGvpp# create sub TenGigabitEthernet3/0/0 10
DBGvpp# lcp create TenGigabitEthernet3/0/0 host-if e0
DBGvpp# lcp create TenGigabitEthernet3/0/0.10 host-if e0.10
602: e0: <BROADCAST,MULTICAST> mtu 9000 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 9000 qdisc noop state DOWN mode DEFAULT group default qlen 1000

DBGvpp# set interface mtu packet 9216 TenGigabitEthernet3/0/0
602: e0: <BROADCAST,MULTICAST> mtu 9216 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 9000 qdisc noop state DOWN mode DEFAULT group default qlen 1000

DBGvpp# set interface mtu packet 9050 TenGigabitEthernet3/0/0
602: e0: <BROADCAST,MULTICAST> mtu 9050 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 9000 qdisc noop state DOWN mode DEFAULT group default qlen 1000

DBGvpp# set interface mtu packet 9050 TenGigabitEthernet3/0/0.10
602: e0: <BROADCAST,MULTICAST> mtu 9050 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 9050 qdisc noop state DOWN mode DEFAULT group default qlen 1000

DBGvpp# set interface mtu packet 1500 TenGigabitEthernet3/0/0.10
602: e0: <BROADCAST,MULTICAST> mtu 9050 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000

DBGvpp# set interface mtu packet 1500 TenGigabitEthernet3/0/0
602: e0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
603: e0.10@e0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
---
 lcpng_if_sync.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/lcpng_if_sync.c b/lcpng_if_sync.c
index ff93c24..2f61c06 100644
--- a/lcpng_if_sync.c
+++ b/lcpng_if_sync.c
@@ -95,3 +95,30 @@ lcp_itf_admin_state_change (vnet_main_t * vnm, u32 sw_if_index, u32 flags)
 }   
 
 VNET_SW_INTERFACE_ADMIN_UP_DOWN_FUNCTION(lcp_itf_admin_state_change);
+
+static clib_error_t *
+lcp_itf_mtu_change (vnet_main_t *vnm, u32 sw_if_index, u32 flags)
+{
+  const lcp_itf_pair_t *lip;
+  vnet_sw_interface_t *si;
+
+  LCP_ITF_PAIR_DBG ("mtu_change: sw %U %u", format_vnet_sw_if_index_name, vnm,
+		    sw_if_index, flags);
+
+  // Sync interface state changes into host
+  lip = lcp_itf_pair_get (lcp_itf_pair_find_by_phy (sw_if_index));
+  if (!lip)
+    return NULL;
+
+  si = vnet_get_sw_interface_or_null (vnm, sw_if_index);
+  if (!si)
+    return NULL;
+
+  LCP_ITF_PAIR_INFO ("mtu_change: %U mtu %u", format_lcp_itf_pair, lip,
+		     si->mtu[VNET_MTU_L3]);
+  vnet_netlink_set_link_mtu (lip->lip_vif_index, si->mtu[VNET_MTU_L3]);
+
+  return NULL;
+}
+
+VNET_SW_INTERFACE_MTU_CHANGE_FUNCTION (lcp_itf_mtu_change);