Support ELL 0.68 l_netlink_message API. (#303)

* configure: Check for l_netlink_message_new_sized()

ELL 0.68 introduced a non-backward compatible change to its API by
introducing a new l_netlink_message API to simplify use of the
l_netlink_send() function.  Check for the existence of the new API in
the mptcpd configure script.

* network_monitor: Support ELL l_netlink_message API

Support both the pre- and post- ELL 0.68 versions of l_netlink_send()
function.

* network_monitor: Refactor l_netlink_send() calls.

Refactor #ifdef blocks containing calls to the pre- and post-0.68
ELL l_netlink_send() calls to a separate helper functions.  This
simplifies the code, and obviates the need to have an #ifdef block
each time l_netlink_send() is called.  Many thanks to Matthieu Baerts
for making this suggestion.

* configure: Bump copyright year.

configure.ac

@@ -2,7 +2,7 @@
 #                                               -*- Autoconf -*-
 # Process this file with autoconf to produce a configure script.
 #
-# Copyright (c) 2017-2023, Intel Corporation
+# Copyright (c) 2017-2024, Intel Corporation
 
 AC_PREREQ([2.69])
 AC_INIT([mptcpd],
@@ -265,6 +265,12 @@ AC_CHECK_FUNC([l_hashmap_replace],
               [AC_DEFINE([HAVE_L_HASHMAP_REPLACE],
                          [],
                          [ELL has l_hashmap_replace()])])
+
+dnl l_netlink_message_new_sized() was introduced in ELL v0.68.
+AC_CHECK_FUNC([l_netlink_message_new_sized],
+              [AC_DEFINE([HAVE_L_NETLINK_MESSAGE_NEW_SIZED],
+                         [],
+                         [ELL has l_netlink_message_new_sized()])])
 LIBS=$mptcpd_save_libs
 
 # ---------------------------------------------------------------

lib/network_monitor.c

@@ -4,7 +4,7 @@
  *
  * @brief mptcpd network device monitoring.
  *
- * Copyright (c) 2017-2022, Intel Corporation
+ * Copyright (c) 2017-2022, 2024, Intel Corporation
  */
 
 #ifdef HAVE_CONFIG_H
@@ -95,6 +95,51 @@ struct mptcpd_nm
         bool monitor_loopback;
 };
 
+// -------------------------------------------------------------------
+//                         Helper Functions
+// -------------------------------------------------------------------
+
+/**
+ * @brief Wrap different versions of ELL @c l_netlink_send().
+ *
+ * ELL 0.68 changed the API for @c l_netlink_send().  This helper
+ * function wraps the two different function calls so that mptcpd will
+ * work with both pre- and post-0.68 @c l_netlink_send() APIs.
+ */
+static unsigned int netlink_send(struct l_netlink *netlink,
+                                 uint16_t type,
+                                 uint16_t flags,
+                                 void const *data,
+                                 uint32_t len,
+                                 l_netlink_command_func_t function,
+                                 void *user_data,
+                                 l_netlink_destroy_func_t destroy)
+{
+#ifdef HAVE_L_NETLINK_MESSAGE_NEW_SIZED
+        // ELL >= 0.68
+        struct l_netlink_message *const message =
+                l_netlink_message_new_sized(type, flags, len);
+
+        l_netlink_message_add_header(message, data, len);
+
+        return l_netlink_send(netlink,
+                              message,
+                              function,
+                              user_data,
+                              destroy);
+#else
+        // ELL < 0.68
+        return l_netlink_send(netlink,
+                              type,
+                              flags,
+                              data,
+                              len,
+                              function,
+                              user_data,
+                              destroy);
+#endif
+}
+
 // -------------------------------------------------------------------
 //               Network Address Information Handling
 // -------------------------------------------------------------------
@@ -1015,14 +1060,14 @@ static void check_default_route(struct nm_addr_info *ai)
          */
         mptcpd_addr_get(ai);
 
-        if (l_netlink_send(ai->nm->rtnl,
-                           RTM_GETROUTE,
-                           0,
-                           &store,
-                           buf - (char *) &store,
-                           handle_rtm_getroute,
-                           ai,
-                           NULL) == 0) {
+        if (netlink_send(ai->nm->rtnl,
+                         RTM_GETROUTE,
+                         0,
+                         &store,
+                         buf - (char *) &store,
+                         handle_rtm_getroute,
+                         ai,
+                         NULL) == 0) {
                 l_debug("Route lookup failed");
                 mptcpd_addr_put(ai);
         }
@@ -1388,14 +1433,14 @@ static void send_getaddr_command(void *user_data)
 
         // Get IP addresses.
         struct ifaddrmsg addr_msg = { .ifa_family = AF_UNSPEC };
-        if (l_netlink_send(nm->rtnl,
-                           RTM_GETADDR,
-                           NLM_F_DUMP,
-                           &addr_msg,
-                           sizeof(addr_msg),
-                           handle_rtm_getaddr,
-                           nm,
-                           NULL) == 0) {
+        if (netlink_send(nm->rtnl,
+                         RTM_GETADDR,
+                         NLM_F_DUMP,
+                         &addr_msg,
+                         sizeof(addr_msg),
+                         handle_rtm_getaddr,
+                         nm,
+                         NULL) == 0) {
                 l_error("Unable to obtain IP addresses.");
 
                 /*
@@ -1481,14 +1526,14 @@ struct mptcpd_nm *mptcpd_nm_create(uint32_t flags)
          *       resulted in an EBUSY error.
          */
         struct ifinfomsg link_msg = { .ifi_family = AF_UNSPEC };
-        if (l_netlink_send(nm->rtnl,
-                           RTM_GETLINK,
-                           NLM_F_DUMP,
-                           &link_msg,
-                           sizeof(link_msg),
-                           handle_rtm_getlink,
-                           nm,
-                           send_getaddr_command)
+        if (netlink_send(nm->rtnl,
+                         RTM_GETLINK,
+                         NLM_F_DUMP,
+                         &link_msg,
+                         sizeof(link_msg),
+                         handle_rtm_getlink,
+                         nm,
+                         send_getaddr_command)
             == 0) {
                 l_error("Unable to obtain network devices.");
                 mptcpd_nm_destroy(nm);