Enable ARP Update Script for Packet based chassis. (#11465)

What I did:

    Following changes done for packet based chassis:-
    1> Run arp_update on LC's to resolve static route nexthops over backend
    port-channel interfaces.
    2> On Supervisor make sure arp_update exit gracefully

dockers/docker-orchagent/docker-init.j2

@@ -21,7 +21,7 @@ CFGGEN_PARAMS=" \
     -t /usr/share/sonic/templates/wait_for_link.sh.j2,/usr/bin/wait_for_link.sh \
 "
 VLAN=$(sonic-cfggen $CFGGEN_PARAMS)
-
+SWITCH_TYPE=${SWITCH_TYPE:-`sonic-cfggen -d -v "DEVICE_METADATA['localhost']['switch_type']"`}
 chmod +x /usr/bin/wait_for_link.sh
 
 # Executed platform specific initialization tasks.
@@ -34,9 +34,12 @@ if [ -x /usr/share/sonic/hwsku/hwsku-init ]; then
     /usr/share/sonic/hwsku/hwsku-init
 fi
 
-# Start arp_update and NDP proxy daemon when VLAN exists
+# Start arp update when VLAN exists or switch type as chassis packet for backend port channel interfaces
-if [ "$VLAN" != "" ]; then
+if [[ "$VLAN" != "" ]] || [[ "$SWITCH_TYPE" == "chassis-packet" ]]; then
     cp /usr/share/sonic/templates/arp_update.conf /etc/supervisor/conf.d/
+fi
+
+if [ "$VLAN" != "" ]; then
     cp /usr/share/sonic/templates/ndppd.conf /etc/supervisor/conf.d/
 fi
 

files/build_templates/arp_update_vars.j2

@@ -1,6 +1,8 @@
 {
+    "switch_type": "{% if DEVICE_METADATA and 'localhost' in DEVICE_METADATA and 'switch_type' in DEVICE_METADATA['localhost'] %}{{ DEVICE_METADATA['localhost']['switch_type'] }}{%endif %}",
     "interface": "{% for (name, prefix) in INTERFACE|pfx_filter %}{% if prefix|ipv6 %}{{ name }} {% endif %}{% endfor %}",
     "pc_interface" : "{% for (name, prefix) in PORTCHANNEL_INTERFACE|pfx_filter %}{% if prefix|ipv6 %}{{ name }} {% endif %}{% endfor %}",
     "vlan_sub_interface": "{% for (name, prefix) in VLAN_SUB_INTERFACE|pfx_filter %}{% if prefix|ipv6 %}{{ name }} {% endif %}{% endfor %}",
-    "vlan" : "{% if VLAN %}{{ VLAN.keys() | join(' ') }}{% endif %}"
+    "vlan" : "{% if VLAN %}{{ VLAN.keys() | join(' ') }}{% endif %}",
+    "static_route_nexthops": "{% if STATIC_ROUTE %}{% for static_route_prefix, static_route_attr in STATIC_ROUTE.items() %}{%- if static_route_prefix -%}{{ static_route_attr['nexthop'].split(',') | join(' ') | lower + " " }}{%- endif -%}{% endfor %}{% endif %}"
 }

files/scripts/arp_update

@@ -12,6 +12,34 @@ ARP_UPDATE_VARS_FILE="/usr/share/sonic/templates/arp_update_vars.j2"
 while /bin/true; do
   # find L3 interfaces which are UP, send ipv6 multicast pings
   ARP_UPDATE_VARS=$(sonic-cfggen -d -t ${ARP_UPDATE_VARS_FILE})
+  SWITCH_TYPE=$(echo $ARP_UPDATE_VARS | jq -r '.switch_type')
+  if [[ "$SWITCH_TYPE" == "chassis-packet" ]]; then
+      STATIC_ROUTE_NEXTHOPS=$(echo $ARP_UPDATE_VARS | jq -r '.static_route_nexthops')
+      # on supervisor/rp exit the script gracefully
+      if [[ -z "$STATIC_ROUTE_NEXTHOPS" ]]; then
+          logger "arp_update: exiting as no static route in packet based chassis"
+          exit 0
+      fi
+      for nexthop in $STATIC_ROUTE_NEXTHOPS; do
+          if [[ $nexthop == *"."* ]]; then
+              neigh_state=( $(ip -4 neigh show | grep $nexthop | tr -s ' ' | cut -d ' ' -f 3,4) )
+              ping_prefix=ping
+          elif [[ $nexthop == *":"* ]] ; then
+              neigh_state=( $(ip -6 neigh show | grep $nexthop | tr -s ' ' | cut -d ' ' -f 3,4) )
+              ping_prefix=ping6
+          fi
+       
+          if [[ "${neigh_state[1]}" == "INCOMPLETE" ]] || [[ "${neigh_state[1]}" == "FAILED" ]]; then
+              pingcmd="timeout 0.2 $ping_prefix -I ${neigh_state[0]} -n -q -i 0 -c 1 -W 1 $nexthop >/dev/null"
+              eval $pingcmd
+              logger "arp_update: sttaic route nexthop not resolved, pinging $nexthop on ${neigh_state[0]}"
+          fi
+      done
+
+      sleep 300
+      continue
+  fi
+  # find L3 interfaces which are UP, send ipv6 multicast pings
   INTERFACE=$(echo $ARP_UPDATE_VARS | jq -r '.interface')
   PC_INTERFACE=$(echo $ARP_UPDATE_VARS | jq -r '.pc_interface')
   VLAN_SUB_INTERFACE=$(echo $ARP_UPDATE_VARS | jq -r '.vlan_sub_interface')