Use unix CM as fall-back if netlink isn't there

Sometimes it might happen that netlink sockets aren't available on
runtime (QEmu for example).

libgupnp/gupnp-context-manager.c

@@ -356,15 +356,19 @@ gupnp_context_manager_create (guint port)
                 impl_type = GUPNP_TYPE_CONNMAN_MANAGER;
 #endif
 
-        if (impl_type == G_TYPE_INVALID)
+        if (impl_type == G_TYPE_INVALID) {
             /* Either user requested us to use the Linux CM explicitly or we
              * are using one of the DBus managers but it's not available, so we
              * fall-back to it. */
 #if defined (USE_NETLINK) || defined (HAVE_LINUX_RTNETLINK_H)
-                impl_type = GUPNP_TYPE_LINUX_CONTEXT_MANAGER;
+                if (gupnp_linux_context_manager_is_available ())
+                        impl_type = GUPNP_TYPE_LINUX_CONTEXT_MANAGER;
+                else
+                    impl_type = GUPNP_TYPE_UNIX_CONTEXT_MANAGER;
 #else
                 impl_type = GUPNP_TYPE_UNIX_CONTEXT_MANAGER;
 #endif
+        }
 #endif /* G_OS_WIN32 */
         impl = g_object_new (impl_type,
                              "port", port,

libgupnp/gupnp-linux-context-manager.c

@@ -686,6 +686,21 @@ create_netlink_socket (GUPnPLinuxContextManager *self, GError **error)
         return TRUE;
 }
 
+gboolean
+gupnp_linux_context_manager_is_available (void)
+{
+        int fd = -1;
+
+        fd = socket (PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
+
+        if (fd == -1)
+                return FALSE;
+
+        close (fd);
+
+        return TRUE;
+}
+
 static void
 gupnp_linux_context_manager_init (GUPnPLinuxContextManager *self)
 {

libgupnp/gupnp-linux-context-manager.h

@@ -68,6 +68,8 @@ typedef struct {
         void (* _gupnp_reserved4) (void);
 } GUPnPLinuxContextManagerClass;
 
+G_GNUC_INTERNAL gboolean gupnp_linux_context_manager_is_available (void);
+
 G_END_DECLS
 
 #endif /* __GUPNP_LINUX_CONTEXT_MANAGER_H__ */