log: When using systemd, just log to stdout/stderr

1) This avoids duplicated output since we were using LOG_PERROR
   which writes to both syslog and stderr.
2) syslog() is basically deprecated in the systemd world, so let's
   avoid using it.

In this approach, we also output a level prefix to stderr.

Some adjustments from Simon McVittie

https://bugzilla.gnome.org/show_bug.cgi?id=692308

3 files changed, 74 insertions, 112 deletions

diff --git a/common/Makefile.am b/common/Makefile.am
index c28d9b28..9717db82 100644
--- a/common/Makefile.am
+++ b/common/Makefile.am
@@ -85,9 +85,11 @@ libgdmcommon_la_CPPFLAGS = 		\
 
 libgdmcommon_la_CFLAGS =		\
 	$(COMMON_CFLAGS)		\
+	$(SYSTEMD_CFLAGS)	        \
 	$(NULL)
 
 libgdmcommon_la_LIBADD =		\
+	$(SYSTEMD_LIBS)	        \
 	$(NULL)
 
 libgdmcommon_la_LDFLAGS = 	\
diff --git a/common/gdm-log.c b/common/gdm-log.c
index e9bf4715..22d8c7d6 100644
--- a/common/gdm-log.c
+++ b/common/gdm-log.c
@@ -30,6 +30,9 @@
 #include <unistd.h>
 
 #include <syslog.h>
+#ifdef WITH_SYSTEMD
+#include <systemd/sd-daemon.h>
+#endif
 
 #include <glib.h>
 #include <glib/gstdio.h>
@@ -37,143 +40,87 @@
 #include "gdm-log.h"
 
 static gboolean initialized = FALSE;
-static int      syslog_levels = G_LOG_LEVEL_MASK & ~G_LOG_LEVEL_DEBUG;
+static gboolean is_sd_booted = FALSE;
+static gboolean debug_enabled = FALSE;
 
-static void
-log_level_to_priority_and_prefix (GLogLevelFlags log_level,
-                                  int           *priorityp,
-                                  const char   **prefixp)
+static gint
+get_syslog_priority_from_log_level (GLogLevelFlags log_level)
 {
-        int         priority;
-        const char *prefix;
-
-        /* Process the message prefix and priority */
         switch (log_level & G_LOG_LEVEL_MASK) {
         case G_LOG_FLAG_FATAL:
-                priority = LOG_EMERG;
-                prefix = "FATAL";
-                break;
+                return LOG_EMERG;
         case G_LOG_LEVEL_ERROR:
-                priority = LOG_ERR;
-                prefix = "ERROR";
-                break;
+                /* fatal error - a critical error, in the syslog world */
+                return LOG_CRIT;
         case G_LOG_LEVEL_CRITICAL:
-                priority = LOG_CRIT;
-                prefix = "CRITICAL";
-                break;
+                /* critical warning - an error, in the syslog world */
+                return LOG_ERR;
         case G_LOG_LEVEL_WARNING:
-                priority = LOG_WARNING;
-                prefix = "WARNING";
-                break;
         case G_LOG_LEVEL_MESSAGE:
-                priority = LOG_NOTICE;
-                prefix = "MESSAGE";
-                break;
+                return LOG_NOTICE;
         case G_LOG_LEVEL_INFO:
-                priority = LOG_INFO;
-                prefix = "INFO";
-                break;
+                return LOG_INFO;
         case G_LOG_LEVEL_DEBUG:
-                /* if debug was requested then bump this up to ERROR
-                 * to ensure it is seen in a log */
-                if (syslog_levels & G_LOG_LEVEL_DEBUG) {
-                        priority = LOG_WARNING;
-                        prefix = "DEBUG(+)";
-                } else {
-                        priority = LOG_DEBUG;
-                        prefix = "DEBUG";
-                }
-                break;
         default:
-                priority = LOG_DEBUG;
-                prefix = "UNKNOWN";
-                break;
-        }
-
-        if (priorityp != NULL) {
-                *priorityp = priority;
-        }
-        if (prefixp != NULL) {
-                *prefixp = prefix;
+                return LOG_DEBUG;
         }
 }
 
-void
-gdm_log_default_handler (const gchar   *log_domain,
-                         GLogLevelFlags log_level,
-                         const gchar   *message,
-                         gpointer       unused_data)
+static void
+gdm_log_default_handler (const gchar    *log_domain,
+                         GLogLevelFlags  log_level,
+                         const gchar    *message,
+                         gpointer        unused_data)
 {
-        GString     *gstring;
-        int          priority;
-        const char  *level_prefix;
-        char        *string;
-        gboolean     do_log;
-        gboolean     is_fatal;
+        int priority;
 
-        is_fatal = (log_level & G_LOG_FLAG_FATAL) != 0;
+        gdm_log_init ();
 
-        do_log = (log_level & syslog_levels);
-        if (! do_log) {
+        if ((log_level & G_LOG_LEVEL_MASK) == G_LOG_LEVEL_DEBUG &&
+            !debug_enabled) {
                 return;
         }
 
-        if (! initialized) {
-                gdm_log_init ();
-        }
-
-        log_level_to_priority_and_prefix (log_level,
-                                          &priority,
-                                          &level_prefix);
-
-        gstring = g_string_new (NULL);
-
-        if (log_domain != NULL) {
-                g_string_append (gstring, log_domain);
-                g_string_append_c (gstring, '-');
-        }
-        g_string_append (gstring, level_prefix);
-
-        g_string_append (gstring, ": ");
-        if (message == NULL) {
-                g_string_append (gstring, "(NULL) message");
-        } else {
-                g_string_append (gstring, message);
-        }
-        if (is_fatal) {
-                g_string_append (gstring, "\naborting...\n");
+        /* Process the message prefix and priority */
+        priority = get_syslog_priority_from_log_level (log_level);
+
+        if (is_sd_booted) {
+                fprintf (stderr,
+                         "<%d>%s%s%s\n",
+                         priority,
+                         log_domain != NULL? log_domain : "",
+                         log_domain != NULL? ": " : "",
+                         message);
+                fflush (stderr);
         } else {
-                g_string_append (gstring, "\n");
+                syslog (priority,
+                        "%s%s%s\n",
+                        log_domain != NULL? log_domain : "",
+                        log_domain != NULL? ": " : "",
+                        message);
         }
-
-        string = g_string_free (gstring, FALSE);
-
-        syslog (priority, "%s", string);
-
-        g_free (string);
 }
 
 void
 gdm_log_toggle_debug (void)
 {
-        if (syslog_levels & G_LOG_LEVEL_DEBUG) {
-                g_debug ("Debugging disabled");
-                syslog_levels &= ~G_LOG_LEVEL_DEBUG;
-        } else {
-                syslog_levels |= G_LOG_LEVEL_DEBUG;
-                g_debug ("Debugging enabled");
-        }
+        gdm_log_set_debug (!debug_enabled);
 }
 
 void
 gdm_log_set_debug (gboolean debug)
 {
+        g_assert (initialized);
+        if (debug_enabled == debug) {
+                return;
+        }
+
         if (debug) {
-                syslog_levels |= G_LOG_LEVEL_DEBUG;
+                debug_enabled = debug;
                 g_debug ("Enabling debugging");
         } else {
                 g_debug ("Disabling debugging");
-                syslog_levels &= ~G_LOG_LEVEL_DEBUG;
+                debug_enabled = debug;
         }
 }
 
@@ -183,24 +130,41 @@ gdm_log_init (void)
         const char *prg_name;
         int         options;
 
+        if (initialized)
+                return;
+
+        initialized = TRUE;
+
+#ifdef WITH_SYSTEMD
+        is_sd_booted = sd_booted () > 0;
+#endif
+
         g_log_set_default_handler (gdm_log_default_handler, NULL);
 
-        prg_name = g_get_prgname ();
+        /* Only set up syslog if !systemd, otherwise with systemd
+         * enabled, we keep the default GLib log handler which goes to
+         * stderr, which is routed to the appropriate place in the
+         * systemd service file.
+         */
+        if (!is_sd_booted) {
+                prg_name = g_get_prgname ();
 
-        options = LOG_PID;
+                options = LOG_PID;
 #ifdef LOG_PERROR
-        options |= LOG_PERROR;
+                options |= LOG_PERROR;
 #endif
 
-        openlog (prg_name, options, LOG_DAEMON);
-
-        initialized = TRUE;
+                openlog (prg_name, options, LOG_DAEMON);
+        }
 }
 
 void
 gdm_log_shutdown (void)
 {
-        closelog ();
+        if (!initialized)
+                return;
+        if (!is_sd_booted)
+                closelog ();
         initialized = FALSE;
 }
 
diff --git a/common/gdm-log.h b/common/gdm-log.h
index c7f39769..db6ed873 100644
--- a/common/gdm-log.h
+++ b/common/gdm-log.h
@@ -28,10 +28,6 @@
 
 G_BEGIN_DECLS
 
-void      gdm_log_default_handler (const gchar   *log_domain,
-                                   GLogLevelFlags log_level,
-                                   const gchar   *message,
-                                   gpointer      unused_data);
 void      gdm_log_set_debug       (gboolean       debug);
 void      gdm_log_toggle_debug    (void);
 void      gdm_log_init            (void);