wwan: check at runtime whether to start ModemManager

This makes NetworkManager use runtime detection to manage the
ModemManager lifecycle when not run by systemd. Under systemd, we expect
the ModemManager service to be started by systemd, under non-systemd, we
use the dbus activation feature to start ModemManager.

[thaller@redhat.com: original patch heavily modified to check for available
 libsystemd library]

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=770871
https://mail.gnome.org/archives/networkmanager-list/2016-June/msg00086.html

configure.ac

@@ -375,6 +375,10 @@ elif test "$hostname_persist" = slackware; then
 	AC_DEFINE(HOSTNAME_PERSIST_SLACKWARE, 1, [Enable Slackware hostname persist method])
 fi
 
+PKG_CHECK_MODULES(LIBSYSTEMD, [libsystemd >= 209],
+    [AC_DEFINE([HAVE_LIBSYSTEMD], 1, [Define to 1 if libsystemd is available])],
+    [AC_DEFINE([HAVE_LIBSYSTEMD], 0, [Define to 1 if libsystemd is available])])
+
 AC_ARG_WITH(systemd-journal, AS_HELP_STRING([--with-systemd-journal=yes|no], [Use systemd journal for logging]))
 have_systemd_journal=no
 if test "$with_systemd_journal" != "no"; then

src/devices/wwan/Makefile.am

@@ -16,6 +16,7 @@ AM_CPPFLAGS = \
 	-DG_LOG_DOMAIN=\""NetworkManager-wwan"\" \
 	-DNETWORKMANAGER_COMPILATION=NM_NETWORKMANAGER_COMPILATION_INSIDE_DAEMON \
 	$(GLIB_CFLAGS) \
+	$(LIBSYSTEMD_CFLAGS) \
 	$(MM_GLIB_CFLAGS)
 
 BUILT_SOURCES = $(null)
@@ -49,6 +50,7 @@ libnm_wwan_la_LDFLAGS = \
 libnm_wwan_la_LIBADD = \
 	$(top_builddir)/introspection/libnmdbus.la \
 	$(GLIB_LIBS) \
+	$(LIBSYSTEMD_LIBS) \
 	$(MM_GLIB_LIBS)
 
 ###########################################################

src/devices/wwan/nm-modem-manager.c

@@ -31,6 +31,12 @@
 #include "nm-modem.h"
 #include "nm-modem-broadband.h"
 
+#if HAVE_LIBSYSTEMD
+#include <systemd/sd-daemon.h>
+#else
+#define sd_booted() FALSE
+#endif
+
 #define MODEM_POKE_INTERVAL 120
 
 G_DEFINE_TYPE (NMModemManager, nm_modem_manager, G_TYPE_OBJECT)
@@ -199,10 +205,9 @@ modem_manager_name_owner_changed (MMManager *modem_manager,
 	if (!name_owner) {
 		nm_log_info (LOGD_MB, "ModemManager disappeared from bus");
 
-#if !HAVE_SYSTEMD
 		/* If not managed by systemd, schedule relaunch */
-		schedule_modem_manager_relaunch (self, 0);
-#endif
+		if (!sd_booted ())
+			schedule_modem_manager_relaunch (self, 0);
 
 		return;
 	}
@@ -223,8 +228,6 @@ modem_manager_name_owner_changed (MMManager *modem_manager,
 	 */
 }
 
-#if !HAVE_SYSTEMD
-
 static void
 modem_manager_poke_cb (GDBusConnection *connection,
                        GAsyncResult *res,
@@ -273,8 +276,6 @@ modem_manager_poke (NMModemManager *self)
 	                        g_object_ref (self)); /* user_data */
 }
 
-#endif /* HAVE_SYSTEMD */
-
 static void
 modem_manager_check_name_owner (NMModemManager *self)
 {
@@ -288,10 +289,9 @@ modem_manager_check_name_owner (NMModemManager *self)
 		return;
 	}
 
-#if !HAVE_SYSTEMD
 	/* If the lifecycle is not managed by systemd, poke */
-	modem_manager_poke (self);
-#endif
+	if (!sd_booted ())
+		modem_manager_poke (self);
 }
 
 static void