log: Add support for journal logging

This logging is available if the software was build with the configure
option --with-systemd-journal.

It will be enabled by default if libsystemd is found.

The runtime parameter --log-journal enables to output of log messages
to the systemd journal.

Please note that the journal priority field has the same value as the
syslog level so no conversion is required here.

src/mm-log.c

@@ -35,6 +35,11 @@
 #include <libmbim-glib.h>
 #endif
 
+#if defined WITH_SYSTEMD_JOURNAL
+#define SD_JOURNAL_SUPPRESS_LOCATION
+#include <systemd/sd-journal.h>
+#endif
+
 #include "mm-log.h"
 
 enum {
@@ -148,6 +153,43 @@ log_backend_syslog (const char *loc,
     syslog (syslog_level, "%s", message);
 }
 
+#if defined WITH_SYSTEMD_JOURNAL
+static void
+log_backend_systemd_journal (const char *loc,
+                             const char *func,
+                             int syslog_level,
+                             const char *message,
+                             size_t length)
+{
+    const char *line;
+    size_t file_length;
+
+    if (loc == NULL) {
+        sd_journal_send ("MESSAGE=%s", message,
+                         "PRIORITY=%d", syslog_level,
+                         NULL);
+        return;
+    }
+
+    line = strstr (loc, ":");
+    if (line) {
+        file_length = line - loc;
+        line++;
+    } else {
+        /* This is not supposed to happen but we must be prepared for this */
+        line = loc;
+        file_length = 0;
+    }
+
+    sd_journal_send ("MESSAGE=%s", message,
+                     "PRIORITY=%d", syslog_level,
+                     "CODE_FUNC=%s", func,
+                     "CODE_FILE=%.*s", file_length, loc,
+                     "CODE_LINE=%s", line,
+                     NULL);
+}
+#endif
+
 void
 _mm_log (const char *loc,
          const char *func,
@@ -242,6 +284,7 @@ mm_log_set_level (const char *level, GError **error)
 gboolean
 mm_log_setup (const char *level,
               const char *log_file,
+              gboolean log_journal,
               gboolean show_timestamps,
               gboolean rel_timestamps,
               GError **error)
@@ -258,6 +301,12 @@ mm_log_setup (const char *level,
     /* Grab start time for relative timestamps */
     g_get_current_time (&rel_start);
 
+#if defined WITH_SYSTEMD_JOURNAL
+    if (log_journal) {
+        log_backend = log_backend_systemd_journal;
+        append_log_level_text = FALSE;
+    } else
+#endif
     if (log_file == NULL) {
         openlog (G_LOG_DOMAIN, LOG_CONS | LOG_PID | LOG_PERROR, LOG_DAEMON);
         log_backend = log_backend_syslog;