From c0d99472c194afcd486b45477ceefd619e4a351f Mon Sep 17 00:00:00 2001
From: Kamil Cudnik <kcudnik@gmail.com>
Date: Fri, 13 Mar 2020 18:18:26 +0100
Subject: [PATCH] [vs] Fix setting correct port mtu value (#573)

---
 vslib/src/SwitchStateBase.cpp       | 21 +++++++++++++++++++++
 vslib/src/SwitchStateBaseHostif.cpp | 20 +++++++++++++++++---
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/vslib/src/SwitchStateBase.cpp b/vslib/src/SwitchStateBase.cpp
index 1a92ac8254ae..8ac4c6486a86 100644
--- a/vslib/src/SwitchStateBase.cpp
+++ b/vslib/src/SwitchStateBase.cpp
@@ -393,6 +393,27 @@ sai_status_t SwitchStateBase::setPort(
             }
         }
     }
+    else if (attr && attr->id == SAI_PORT_ATTR_MTU && m_switchConfig->m_useTapDevice)
+    {
+        uint32_t mtu = attr->value.u32;
+
+        std::string name;
+
+        if (getTapNameFromPortId(portId, name))
+        {
+            SWSS_LOG_INFO("setting new MTU: %d on %s", mtu, name.c_str());
+
+            std::string vname = vs_get_veth_name(name, portId);
+
+            if (vs_set_dev_mtu(name.c_str(), mtu) < 0 || vs_set_dev_mtu(vname.c_str(), mtu) < 0)
+            {
+                SWSS_LOG_ERROR("failed to set MTU on portId %s",
+                    sai_serialize_object_id(portId).c_str());
+
+                return SAI_STATUS_FAILURE;
+            }
+        }
+    }
 
     auto sid = sai_serialize_object_id(portId);
 
diff --git a/vslib/src/SwitchStateBaseHostif.cpp b/vslib/src/SwitchStateBaseHostif.cpp
index fff2d0286626..1d25afd7817b 100644
--- a/vslib/src/SwitchStateBaseHostif.cpp
+++ b/vslib/src/SwitchStateBaseHostif.cpp
@@ -634,15 +634,29 @@ sai_status_t SwitchStateBase::vs_create_hostif_tap_interface(
         return SAI_STATUS_FAILURE;
     }
 
-    vs_set_dev_mtu(name.c_str(), ETH_FRAME_BUFFER_SIZE);
+    std::string vname = vs_get_veth_name(name, obj_id);
+
+    int mtu = ETH_FRAME_BUFFER_SIZE;
+
+    sai_attribute_t attrmtu;
+
+    attrmtu.id = SAI_PORT_ATTR_MTU;
+
+    if (get(SAI_OBJECT_TYPE_PORT, obj_id, 1, &attrmtu) == SAI_STATUS_SUCCESS)
+    {
+        mtu = attrmtu.value.u32;
+
+        SWSS_LOG_INFO("setting new MTU: %d on %s", mtu, vname.c_str());
+    }
+
+    vs_set_dev_mtu(name.c_str(), mtu);
+    vs_set_dev_mtu(vname.c_str(), mtu);
 
     if (!hostif_create_tap_veth_forwarding(name, tapfd, obj_id))
     {
         SWSS_LOG_ERROR("forwarding rule on %s was not added", name.c_str());
     }
 
-    std::string vname = vs_get_veth_name(name, obj_id);
-
     SWSS_LOG_INFO("mapping interface %s to port id %s",
             vname.c_str(),
             sai_serialize_object_id(obj_id).c_str());