Add systemd notification support to olad v2

Changes from v1:

- Systemd support is now switched in via a flag to the configure script.
- Failures to notify systemd are logged, but only when the notification
  socket is actually passed.
- If the socket is not passed, a warning is displayed.
- Added a utility library for the sd_notify calls.

Author: shenghaoyang

configure.ac

@@ -387,13 +387,6 @@ esac
 have_libftd2xx="no"
 AM_CONDITIONAL([HAVE_LIBFTD2XX], [test "x$have_libftd2xx" = xyes])
 
-# libsystemd
-AC_SEARCH_LIBS([sd_notify], [systemd], [have_libsystemd="yes"])
-AC_CHECK_HEADER([systemd/sd-daemon.h], [], [have_libsystemd="no"])
-
-AS_IF([test "x$have_libsystemd" = xyes],
-      [AC_DEFINE([HAVE_LIBSYSTEMD], [1], [define if libsystemd is installed])])
-
 # ncurses
 AC_CHECK_LIB([ncurses], [initscr], [have_ncurses="yes"])
 AM_CONDITIONAL([HAVE_NCURSES], [test "x$have_ncurses" = xyes])
@@ -751,6 +744,21 @@ AC_ARG_ENABLE(
   [AS_HELP_STRING([--disable-doxygen-version],
   [Substitute the Doxygen version with latest, for the website])])
 
+# systemd support
+AC_ARG_ENABLE(
+  [systemd],
+  [AS_HELP_STRING([--enable-systemd], [Enable systemd support])])
+
+have_libsystemd="no"
+AS_IF([test "x$enable_systemd" = "xyes"],
+  [PKG_CHECK_MODULES([libsystemd], [libsystemd >= 38], [have_libsystemd="yes"])
+   AC_CHECK_HEADER([systemd/sd-daemon.h], [], [have_libsystemd="no"])])
+
+AS_IF([test "x$have_libsystemd" = xyes],
+      [AC_DEFINE([HAVE_LIBSYSTEMD], [1], [define if systemd support wanted])])
+
+AM_CONDITIONAL([HAVE_LIBSYSTEMD], [test "x$have_libsystemd" = xyes])
+
 # UUCP Lock directory
 AC_ARG_WITH([uucp-lock],
             [AS_HELP_STRING([--with-uucp-lock],

olad/Makefile.mk

@@ -42,6 +42,11 @@ ola_server_sources += olad/HttpServerActions.cpp \
 ola_server_additional_libs += common/http/libolahttp.la
 endif
 
+if HAVE_LIBSYSTEMD
+ola_server_sources += olad/NotifySystemd.cpp olad/Systemd.h
+ola_server_additional_libs += $(libsystemd_LIBS)
+endif
+
 # lib olaserver
 lib_LTLIBRARIES += olad/libolaserver.la
 

olad/NotifySystemd.cpp

@@ -0,0 +1,51 @@
+/*
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * NotifySystemd.cpp
+ * Provides wrapped access to the systemd notification interface.
+ * Copyright (C) 2018 Shenghao Yang
+ */
+
+#if HAVE_CONFIG_H
+#include <config.h>
+#endif  // HAVE_CONFIG_H
+
+#if HAVE_LIBSYSTEMD
+#include <systemd/sd-daemon.h>
+#include <errno.h>
+#include <string.h>
+#endif  // HAVE_LIBSYSTEMD
+
+#include "ola/Logging.h"
+
+#include "olad/Systemd.h"
+
+namespace ola {
+
+int notify_systemd(int unset_environment, const char *state) {
+  int rtn = sd_notify(unset_environment, state);
+  if (rtn < 0) {
+    char buf[1024];
+    OLA_WARN << "Error sending notification to systemd: " <<
+      strerror_r(-rtn, buf, sizeof(buf));
+  }
+  return rtn;
+}
+
+bool notify_available() {
+  return (sd_notify(0, "") != 0);
+}
+
+}  // namespace ola

olad/OlaServer.cpp

@@ -22,10 +22,6 @@
 #include <config.h>
 #endif  // HAVE_CONFIG_H
 
-#ifdef HAVE_LIBSYSTEMD
-#include <systemd/sd-daemon.h>
-#endif  // HAVE_LIBSYSTEMD
-
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
@@ -67,6 +63,10 @@
 #include "olad/OladHTTPServer.h"
 #endif  // HAVE_LIBMICROHTTPD
 
+#ifdef HAVE_LIBSYSTEMD
+#include "olad/Systemd.h"
+#endif  // HAVE_LIBSYSTEMD
+
 DEFINE_s_uint16(rpc_port, r, ola::OlaServer::DEFAULT_RPC_PORT,
                 "The port to listen for RPCs on. Defaults to 9010.");
 DEFINE_default_bool(register_with_dns_sd, true,
@@ -477,15 +477,13 @@ bool OlaServer::InternalNewConnection(
 
 void OlaServer::ReloadPluginsInternal() {
 #ifdef HAVE_LIBSYSTEMD
-  // Return value is intentionally not checked for both calls.
-  // See return value section under sd_notify(3).
-  sd_notify(0, "RELOADING=1\nSTATUS=Reloading plugins\n");
+  ola::notify_systemd(0, "RELOADING=1\nSTATUS=Reloading plugins\n");
 #endif  // HAVE_LIBSYSTEMD
   OLA_INFO << "Reloading plugins";
   StopPlugins();
   m_plugin_manager->LoadAll();
 #ifdef HAVE_LIBSYSTEMD
-  sd_notify(0, "READY=1\nSTATUS=Plugin reload complete\n");
+  ola::notify_systemd(0, "READY=1\nSTATUS=Plugin reload complete\n");
 #endif  // HAVE_LIBSYSTEMD
 }
 

olad/Olad.cpp

@@ -24,10 +24,6 @@
 #include <config.h>
 #endif  // HAVE_CONFIG_H
 
-#if HAVE_LIBSYSTEMD
-#include <systemd/sd-daemon.h>
-#endif  // HAVE_LIBSYSTEMD
-
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -40,6 +36,10 @@
 // which needs to be after WinSock2.h, hence this order
 #include "olad/OlaDaemon.h"
 
+#if HAVE_LIBSYSTEMD
+#include "olad/Systemd.h"
+#endif  // HAVE_LIBSYSTEMD
+
 #include "ola/Logging.h"
 #include "ola/base/Credentials.h"
 #include "ola/base/Flags.h"
@@ -176,9 +176,14 @@ int main(int argc, char *argv[]) {
 #endif  // _WIN32
 
 #if HAVE_LIBSYSTEMD
-  // Return value is intentionally not checked. See return value section
-  // under sd_notify(3).
-  sd_notify(0, "READY=1\nSTATUS=Startup complete\n");
+  if (ola::notify_available()) {
+    OLA_INFO << "Systemd notification socket present. Sending notifications.";
+  } else {
+    OLA_WARN << "Systemd notification socket not present";
+  }
+  // Does not need to be guarded. sd_notify does its own internal check on
+  // the socket's presence, as well.
+  ola::notify_systemd(0, "READY=1\nSTATUS=Startup complete\n");
 #endif  // HAVE_LIBSYSTEMD
   olad->Run();
   return ola::EXIT_OK;

olad/Systemd.h

@@ -0,0 +1,46 @@
+/*
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Systemd.h
+ * Interface to systemd functionality.
+ * Copyright (C) 2018 Shenghao Yang
+ */
+
+#ifndef OLAD_SYSTEMD_H_
+#define OLAD_SYSTEMD_H_
+
+namespace ola {
+
+/*
+ * @brief Notify systemd about daemon state changes.
+ *  
+ * This function logs on failures to queue notifications, but only if the
+ * notification socket environment variable is set.
+ *  
+ * @param unset_environment whether to unset the notification socket environment
+ *        variable so child processes cannot utilize it.
+ * @param state state block to pass to systemd.
+ * @return value returned from \ref sd_notify()
+ */
+int notify_systemd(int unset_environment, const char *state);
+
+/* 
+ * @brief Tests whether the systemd notification socket is available.
+ * @return @code true if the socket is available, @code false if not.
+ */
+bool notify_available();
+
+}  // namespace ola
+#endif  // OLAD_SYSTEMD_H_