Use netlink to detect going online

Integrates libnl to detect adding routes. When a route is added, the
offline status of all back ends is reset. This patch adds no heuristics
to detect whether back end went offline.

Fixes: #456

1 files changed, 36 insertions, 0 deletions

diff --git a/src/external/libnl.m4 b/src/external/libnl.m4
new file mode 100644
index 000000000..ed8f95b63
--- /dev/null
+++ b/src/external/libnl.m4
@@ -0,0 +1,36 @@
+dnl A macro to check the availability and version of libnetlink
+AC_DEFUN([AM_CHECK_LIBNL],
+[
+    PKG_CHECK_MODULES(libnl, libnl-1)
+
+    AC_CHECK_HEADERS(netlink.h)
+    AC_CHECK_LIB(nl, nl_connect, [ LIBNL_LIBS="-lnl" ], [AC_MSG_ERROR([libnl is required])])
+
+    AC_CHECK_LIB([nl],
+                 [nl_handle_get_fd],
+                 [AC_DEFINE([HAVE_LIBNL_OLDER_THAN_1_1], 1, [Does libnl have pre-1.1 API?])
+                 ],
+    )
+
+    dnl Check if this particular version of libnl supports particular functions
+    AC_CHECK_LIB([nl],
+                 [nl_socket_add_membership],
+                 [AC_DEFINE([HAVE_NL_SOCKET_ADD_MEMBERSHIP], 1, [Does libnl have nl_socket_add_membership?])
+                 ],
+    )
+
+    AC_CHECK_LIB([nl],
+                 [nl_socket_modify_cb],
+                 [AC_DEFINE([HAVE_NL_SOCKET_MODIFY_CB], 1, [Does libnl have nl_socket_modify_cb?])
+                 ],
+    )
+
+    AC_CHECK_LIB([nl],
+                 [nl_set_passcred],
+                 [AC_DEFINE([HAVE_NL_SET_PASSCRED], 1, [Does libnl have nl_set_passcred?])
+                 ],
+    )
+
+    AC_SUBST(LIBNL_CFLAGS)
+    AC_SUBST(LIBNL_LIBS)
+])