logging: introduce 'systemd-journal' target

This change implements 'systemd-journal' logging target, that is
similar to the existing 'syslog' target.  The key difference is
that 'systemd-journal' allows us to offload rendering of the meta
information, such as location (file name, line number), subsystem,
and logging level, to systemd.  Moreover, we can attach arbitrary,
user-specific fields [1] to the logging messages, so they can be
used for advanced log filtering (e.g. by IMSI/TMSI/TLLI):

  $ journalctl OSMO_SUBSYS=DMSC -f

Since we don't want to make libsystemd a required dependency, this
feature is optional, and needs to be enabled at build-time:

  $ ./configure --enable-systemd-logging

The new logging target can be configured in the same way as any
other one - via the VTY interface, or using the configuration file:

  log systemd-journal [raw]
    logging level set-all notice
    logging filter all 1

Two logging handlers are available: generic and raw.  The first one
behaves similarly to both 'syslog' and 'stderr', i.e. all the meta
information is rendered by libosmocore itself, and then passed to
systemd together with the logging message.  The later is more like
the 'gsmtap' target, so all available meta information is handed
over to systemd in form of fields [1]:

  - CODE_FILE / CODE_LINE - location info,
  - PRIORITY - syslog-compatible logging level,
  - OSMO_SUBSYS - Osmocom-specific sub-system (e.g. DMSC),
  - OSMO_SUBSYS_HEX - same as OSMO_SUBSYS, but encoded in hex,
  - MESSAGE - the logging message itself,

and then can be rendered in any supported format (e.g. JSON).

More details about the API can be found in [2].

[1] https://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html
[2] https://www.freedesktop.org/software/systemd/man/sd-journal.html

Change-Id: I609f5cf438e6ad9038d8fc95f00add6aac29fb23

1 files changed, 65 insertions, 0 deletions

diff --git a/src/vty/logging_vty.c b/src/vty/logging_vty.c
index 200b45a1..02823504 100644
--- a/src/vty/logging_vty.c
+++ b/src/vty/logging_vty.c
@@ -732,6 +732,64 @@ DEFUN(cfg_no_log_syslog, cfg_no_log_syslog_cmd,
 }
 #endif /* HAVE_SYSLOG_H */
 
+DEFUN(cfg_log_systemd_journal, cfg_log_systemd_journal_cmd,
+      "log systemd-journal [raw]",
+      LOG_STR "Logging to systemd-journal\n"
+      "Offload rendering of the meta information (location, category) to systemd\n")
+{
+#ifdef ENABLE_SYSTEMD_LOGGING
+	struct log_target *tgt;
+	bool raw = argc > 0;
+
+	log_tgt_mutex_lock();
+	tgt = log_target_find(LOG_TGT_TYPE_SYSTEMD, NULL);
+	if (tgt == NULL) {
+		tgt = log_target_create_systemd(raw);
+		if (tgt == NULL) {
+			vty_out(vty, "%% Unable to create systemd-journal "
+				"log target%s", VTY_NEWLINE);
+			RET_WITH_UNLOCK(CMD_WARNING);
+		}
+		log_add_target(tgt);
+	} else if (tgt->sd_journal.raw != raw) {
+		log_target_systemd_set_raw(tgt, raw);
+	}
+
+	vty->index = tgt;
+	vty->node = CFG_LOG_NODE;
+
+	RET_WITH_UNLOCK(CMD_SUCCESS);
+#else
+	vty_out(vty, "%% systemd-journal logging is not available "
+		"in this build of libosmocore%s", VTY_NEWLINE);
+	return CMD_WARNING;
+#endif /* ENABLE_SYSTEMD_LOGGING */
+}
+
+DEFUN(cfg_no_log_systemd_journal, cfg_no_log_systemd_journal_cmd,
+	"no log systemd-journal",
+	NO_STR LOG_STR "Logging to systemd-journal\n")
+{
+#ifdef ENABLE_SYSTEMD_LOGGING
+	struct log_target *tgt;
+
+	log_tgt_mutex_lock();
+	tgt = log_target_find(LOG_TGT_TYPE_SYSTEMD, NULL);
+	if (!tgt) {
+		vty_out(vty, "%% No systemd-journal logging active%s", VTY_NEWLINE);
+		RET_WITH_UNLOCK(CMD_WARNING);
+	}
+
+	log_target_destroy(tgt);
+
+	RET_WITH_UNLOCK(CMD_SUCCESS);
+#else
+	vty_out(vty, "%% systemd-journal logging is not available "
+		"in this build of libosmocore%s", VTY_NEWLINE);
+	return CMD_WARNING;
+#endif /* ENABLE_SYSTEMD_LOGGING */
+}
+
 DEFUN(cfg_log_gsmtap, cfg_log_gsmtap_cmd,
 	"log gsmtap [HOSTNAME]",
 	LOG_STR "Logging via GSMTAP\n"
@@ -926,6 +984,11 @@ static int config_write_log_single(struct vty *vty, struct log_target *tgt)
 		vty_out(vty, "log gsmtap %s%s",
 			tgt->tgt_gsmtap.hostname, VTY_NEWLINE);
 		break;
+	case LOG_TGT_TYPE_SYSTEMD:
+		vty_out(vty, "log systemd-journal%s%s",
+			tgt->sd_journal.raw ? " raw" : "",
+			VTY_NEWLINE);
+		break;
 	}
 
 	vty_out(vty, " logging filter all %u%s",
@@ -1127,5 +1190,7 @@ void logging_vty_add_cmds()
 	install_lib_element(CONFIG_NODE, &cfg_log_syslog_local_cmd);
 	install_lib_element(CONFIG_NODE, &cfg_no_log_syslog_cmd);
 #endif
+	install_lib_element(CONFIG_NODE, &cfg_log_systemd_journal_cmd);
+	install_lib_element(CONFIG_NODE, &cfg_no_log_systemd_journal_cmd);
 	install_lib_element(CONFIG_NODE, &cfg_log_gsmtap_cmd);
 }