[pd] deprecate old prefixes in radvd configuration on DHCPv6 PD change (

#2701)

This commit addresses an issue where old prefixes were not being
properly deprecated in the RADVD configuration when the upstream
interface's delegated prefix changed. Previously, only the new prefix
would be advertised, potentially leading to issues for OT still using
the old prefix.

Now, upon a new PD message, dhcpcd.enter-hook will:

- Identify the old and new prefixes: It retrieves the old and new
  prefix information from the dhcpcd environment variables.

- Configure radvd to deprecate the old prefix: If an old prefix exists
  and is different from the new prefix, the radvd.conf file is updated
  to include the old prefix with a preferred and valid lifetime of
  0. This signals to OT that the prefix is deprecated and should no
  longer be used.

- Publish the new prefix: The new prefix is added to radvd.conf with
  the appropriate lifetimes received from the DHCPv6 server.

- Reload radvd: The radvd service is reloaded to apply the changes.

script/reference-device/dhcpcd.enter-hook

@@ -34,26 +34,66 @@ WPAN_INTERFACE="wpan0"
 RADVD_CONF="/etc/radvd.conf"
 LOG_TAG="dhcpcd.enter.hook:"
 
-
 config_ra()
 {
+    local old_prefix="$1"
+    local old_prefix_len="$2"
+    local new_prefix="$3"
+    local new_prefix_len="$4"
+    local new_pltime="$5"
+    local new_vltime="$6"
+
+    local deprecate_old_prefix=false
+    if [ -n "$old_prefix" ] && [ "$old_prefix/$old_prefix_len" != "$new_prefix/$new_prefix_len" ]; then
+        deprecate_old_prefix=true
+    fi
+
+    local publish_new_prefix=false
+    if [ -n "$new_prefix" ] && [ -n "$new_prefix_len" ] && [ -n "$new_pltime" ] && [ -n "$new_vltime" ]; then
+        publish_new_prefix=true
+    fi
+
     logger "$LOG_TAG $reason start config radvd"
 
 sudo tee "${RADVD_CONF}" > /dev/null <<EOF
 interface ${WPAN_INTERFACE}
 {
     IgnoreIfMissing on;
     AdvSendAdvert on;
-    prefix ${1}/${2}
+EOF
+
+    if "$deprecate_old_prefix"; then
+        logger "$LOG_TAG Deprecating old prefix $old_prefix/$old_prefix_len"
+sudo tee -a "${RADVD_CONF}" > /dev/null <<EOF
+    prefix ${old_prefix}/${old_prefix_len}
+    {
+        AdvOnLink on;
+        AdvAutonomous on;
+        AdvRouterAddr off;
+        AdvPreferredLifetime 0;
+        AdvValidLifetime 0;
+    };
+EOF
+    fi
+
+    if $publish_new_prefix; then
+        logger "$LOG_TAG Publishing new prefix $new_prefix/$new_prefix_len  PLTime: $new_pltime  VLTime: $new_vltime"
+sudo tee -a "${RADVD_CONF}" > /dev/null <<EOF
+    prefix ${new_prefix}/${new_prefix_len}
     {
         AdvOnLink on;
         AdvAutonomous on;
         AdvRouterAddr off;
-        AdvPreferredLifetime ${3};
-        AdvValidLifetime ${4};
+        AdvPreferredLifetime ${new_pltime};
+        AdvValidLifetime ${new_vltime};
     };
+EOF
+    fi
+
+sudo tee -a "${RADVD_CONF}" > /dev/null <<EOF
 };
 EOF
+
 }
 
 
@@ -63,17 +103,17 @@ if [ ${interface} = ${UPSTREAM_INTERFACE} ]; then
         # Split the variable into name and value
         name="${var%%=*}"
         value="${var#*=}"
-        logger -t "$LOG_TAG $reason sysenv: " "$name=$value"
+        logger "$LOG_TAG $reason sysenv: $name=$value"
     done
 
     case $reason in
         DELEGATED6 | REBIND6 | RENEW6 | BOUND6 )
-            if [ -z "$new_dhcp6_ia_pd1_prefix1" ] || [ -z "$new_dhcp6_ia_pd1_prefix1_length" ] || \
-               [ -z "$new_dhcp6_ia_pd1_prefix1_pltime" ] || [ -z "$new_dhcp6_ia_pd1_prefix1_vltime" ]; then
-                logger "$LOG_TAG WARNING: Missing DHCPv6 prefix information. Skipping radvd configuration."
-            else
-                logger "$LOG_TAG prefix is $new_dhcp6_ia_pd1_prefix1  length is $new_dhcp6_ia_pd1_prefix1_length pltime is  $new_dhcp6_ia_pd1_prefix1_pltime vltime is $new_dhcp6_ia_pd1_prefix1_vltime"
-                config_ra $new_dhcp6_ia_pd1_prefix1 $new_dhcp6_ia_pd1_prefix1_length $new_dhcp6_ia_pd1_prefix1_pltime  $new_dhcp6_ia_pd1_prefix1_vltime
+            # TODO: Handle multiple IA_PD prefixes (new_dhcp6_ia_pd{i}_prefix{j}, new_dhcp6_ia_pd{i}_prefix{j}_length, etc.)
+            #       and deprecate old prefixes properly for each.  Currently, only one prefix is handled.
+            if { [ -n "$new_dhcp6_ia_pd1_prefix1" ] && [ -n "$new_dhcp6_ia_pd1_prefix1_length" ]; } || \
+               { [ -n "$old_dhcp6_ia_pd1_prefix1" ] && [ -n "$old_dhcp6_ia_pd1_prefix1_length" ]; }; then
+                config_ra "$old_dhcp6_ia_pd1_prefix1" "$old_dhcp6_ia_pd1_prefix1_length" \
+                    "$new_dhcp6_ia_pd1_prefix1" "$new_dhcp6_ia_pd1_prefix1_length" "$new_dhcp6_ia_pd1_prefix1_pltime"  "$new_dhcp6_ia_pd1_prefix1_vltime"
                 if systemctl is-active network.target; then
                     sudo systemctl reload-or-restart radvd || logger "$LOG_TAG Failed to reload radvd"
                 fi

script/reference-device/dhcpcd.exit-hook

@@ -65,7 +65,9 @@ if [ ${interface} = ${UPSTREAM_INTERFACE} ]; then
     done
 
     case $reason in
-        EXPIRE6 | STOP6)
+        EXPIRE6 | STOP6 | RELEASE6 )
+            # TODO: Handle multiple IA_PD prefixes (new_dhcp6_ia_pd{i}_prefix{j}, new_dhcp6_ia_pd{i}_prefix{j}_length, etc.)
+            #       and deprecate old prefixes properly for each.  Currently, only one prefix is handled.)
             if [ -z "$old_dhcp6_ia_pd1_prefix1" ] || [ -z "$old_dhcp6_ia_pd1_prefix1_length" ]; then
                 logger "$LOG_TAG WARNING: Missing DHCPv6 prefix information. Skipping radvd configuration."
             else