add Linux code to adapter-watcher

third-party/rsutils/src/adapter-watcher.cpp

@@ -16,6 +16,13 @@
 #pragma comment( lib, "iphlpapi.lib" )
 
 #else
+
+#include <sys/socket.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <sys/eventfd.h>
+#include <poll.h>
+
 #endif
 
 
@@ -30,9 +37,11 @@ class adapter_watcher_singleton
 
 #ifdef WIN32
     HANDLE _done;
-    std::thread _th;
 #else
+    int _socket;
+    int _done;
 #endif
+    std::thread _th;
 
 public:
     public_signal callbacks;
@@ -42,7 +51,7 @@ class adapter_watcher_singleton
         : _done( CreateEvent(
             nullptr /*security attrs*/, TRUE /*manual reset*/, FALSE /*init unset*/, nullptr /*no name*/ ) )
         , _th(
-              [this]()
+              [this]
               {
                   // We're going to wait on the following handles:
                   HANDLE handles[2];
@@ -78,9 +87,81 @@ class adapter_watcher_singleton
                   CancelIPChangeNotify( &overlap );
               } )
 #else
-        // https://manpages.ubuntu.com/manpages/oracular/en/man7/netlink.7.html
         // https://stackoverflow.com/questions/27008067/how-to-get-notified-about-network-interface-changes-with-netlist-and-rtmgrp-link
-        On Linux, it is done opening and reading on a special kind of socket.Documentation here.Some nice examples here.
+        : _socket( open_netlink() )
+        , _done( eventfd(0, 0) )
+        , _th(
+              [this]
+              {
+                  // We're going to wait on the following handles:
+                  LOG_DEBUG( "starting network adapter watcher" );
+
+		  int const timeout = -1;  // negative value = infinite
+                  int const nfds = 2;
+		  pollfd fds[nfds];
+                  memset( fds, 0, sizeof(fds) );
+		  fds[0].fd = _done;
+		  fds[0].events = POLLIN;
+		  fds[1].fd = _socket;
+		  fds[1].events = POLLIN;
+
+                  while( true )
+                  {
+                      fds[0].revents = 0;
+		      fds[1].revents = 0;
+                      auto rv = poll( fds, nfds, timeout );
+		      if( rv <= 0 )
+		      {
+                          LOG_ERROR( "poll failed: " << rv );
+			  break;
+		      }
+
+		      if( fds[0].revents != 0 )
+                          break;  // we're done
+
+                      LOG_DEBUG( "network adapter changes detected!" );
+
+                      char buf[4096];
+                      struct sockaddr_nl snl;
+                      iovec iov = { buf, sizeof buf };
+                      msghdr msg = { (void*)&snl, sizeof snl, &iov, 1, NULL, 0, 0 };
+                      int status = recvmsg( _socket, &msg, 0 );
+                      if( status < 0 )
+                      {
+                          // Socket non-blocking so bail out once we have read everything
+                          if( errno == EWOULDBLOCK || errno == EAGAIN )
+                              continue;
+
+                          // Anything else is an error
+                          LOG_DEBUG( "read_netlink: Error recvmsg: " << status );
+                          break;
+                      }
+                      if( status == 0 )
+                          LOG_DEBUG( "read_netlink: EOF" );
+
+                      // We need to handle more than one message per recvmsg
+                      for( auto h = (struct nlmsghdr *) buf;
+                           NLMSG_OK( h, (unsigned int)status );
+                           h = NLMSG_NEXT( h, status ) )
+                      {
+                          // Finish reading
+                          if( h->nlmsg_type == NLMSG_DONE )
+                              continue;
+
+                          // Message is some kind of error
+                          if( h->nlmsg_type == NLMSG_ERROR )
+                          {
+                              LOG_DEBUG( "read_netlink: Message is an error - decode TBD" );
+                              continue;
+                          }
+                      }
+
+		      // Call our clients once for all the messages... outside the loop
+                      callbacks.raise();
+                  }
+
+                  LOG_DEBUG( "exiting network adapter watcher" );
+              } )
 #endif
     {
         LOG_DEBUG( "network adapter watcher singleton is up" );
@@ -96,8 +177,39 @@ class adapter_watcher_singleton
         }
         CloseHandle( _done );
 #else
+        if( _th.joinable() )
+	{
+            if( write( _done, &_done, sizeof( &_done ) ) != sizeof( &_done ) )
+		    ;
+            _th.join();
+        }
+        close( _done );
 #endif
     }
+
+#ifndef WIN32
+    static int open_netlink()
+    {
+	// NETLINK_ROUTE
+        //      Receives routing and link updates and may be used to modify the routing tables
+        //      (both IPv4 and IPv6), IP addresses, link parameters, neighbor setups, queueing
+        //      disciplines, traffic classes, and packet classifiers.
+        // https://manpages.ubuntu.com/manpages/oracular/en/man7/netlink.7.html
+        int sock = socket( AF_NETLINK, SOCK_RAW, NETLINK_ROUTE );
+        if( sock < 0 )
+            return sock;
+
+        struct sockaddr_nl addr;
+        memset( (void *)&addr, 0, sizeof( addr ) );
+        addr.nl_family = AF_NETLINK;
+        addr.nl_pid = getpid();
+        addr.nl_groups = RTMGRP_LINK|RTMGRP_IPV4_IFADDR|RTMGRP_IPV6_IFADDR;
+        if( bind( sock, (struct sockaddr *)&addr, sizeof( addr ) ) < 0 )
+            return -1;
+
+        return sock;
+    }
+#endif
 };
 
 static rsutils::shared_ptr_singleton< detail::adapter_watcher_singleton > the_adapter_watcher;