syslogd: make "-O -" log to stdout

function                                             old     new   delta
packed_usage                                       29871   29908     +37
log_locally                                          404     440     +36
syslogd_main                                        1966    1956     -10
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 73/-10)             Total: 63 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

sysklogd/syslogd.c

@@ -21,31 +21,31 @@
 //usage:       "(this version of syslogd ignores /etc/syslog.conf)\n"
 //usage:	)
 //usage:     "\n	-n		Run in foreground"
-//usage:     "\n	-O FILE		Log to FILE (default:/var/log/messages)"
-//usage:     "\n	-l N		Log only messages more urgent than prio N (1-8)"
-//usage:     "\n	-S		Smaller output"
-//usage:	IF_FEATURE_ROTATE_LOGFILE(
-//usage:     "\n	-s SIZE		Max size (KB) before rotation (default:200KB, 0=off)"
-//usage:     "\n	-b N		N rotated logs to keep (default:1, max=99, 0=purge)"
-//usage:	)
 //usage:	IF_FEATURE_REMOTE_LOG(
 //usage:     "\n	-R HOST[:PORT]	Log to HOST:PORT (default PORT:514)"
 //usage:     "\n	-L		Log locally and via network (default is network only if -R)"
 //usage:	)
-//usage:	IF_FEATURE_SYSLOGD_DUP(
-//usage:     "\n	-D		Drop duplicates"
-//usage:	)
 //usage:	IF_FEATURE_IPC_SYSLOG(
 /* NB: -Csize shouldn't have space (because size is optional) */
 //usage:     "\n	-C[size_kb]	Log to shared mem buffer (use logread to read it)"
 //usage:	)
+//usage:	IF_FEATURE_KMSG_SYSLOG(
+//usage:     "\n	-K		Log to kernel printk buffer (use dmesg to read it)"
+//usage:	)
+//usage:     "\n	-O FILE		Log to FILE (default:/var/log/messages, stdout if -)"
+//usage:	IF_FEATURE_ROTATE_LOGFILE(
+//usage:     "\n	-s SIZE		Max size (KB) before rotation (default:200KB, 0=off)"
+//usage:     "\n	-b N		N rotated logs to keep (default:1, max=99, 0=purge)"
+//usage:	)
+//usage:     "\n	-l N		Log only messages more urgent than prio N (1-8)"
+//usage:     "\n	-S		Smaller output"
+//usage:	IF_FEATURE_SYSLOGD_DUP(
+//usage:     "\n	-D		Drop duplicates"
+//usage:	)
 //usage:	IF_FEATURE_SYSLOGD_CFG(
 //usage:     "\n	-f FILE		Use FILE as config (default:/etc/syslog.conf)"
 //usage:	)
 /* //usage:  "\n	-m MIN		Minutes between MARK lines (default:20, 0=off)" */
-//usage:	IF_FEATURE_KMSG_SYSLOG(
-//usage:     "\n	-K		Log to kernel printk buffer (use dmesg to read it)"
-//usage:	)
 //usage:
 //usage:#define syslogd_example_usage
 //usage:       "$ syslogd -R masterlog:514\n"
@@ -585,7 +585,9 @@ static void log_locally(time_t now, char *msg, logFile_t *log_file)
 #endif
 	int len = strlen(msg);
 
-	if (log_file->fd >= 0) {
+	/* fd can't be 0 (we connect fd 0 to /dev/log socket) */
+	/* fd is 1 if "-O -" is in use */
+	if (log_file->fd > 1) {
 		/* Reopen log file every second. This allows admin
 		 * to delete the file and not worry about restarting us.
 		 * This costs almost nothing since it happens
@@ -598,6 +600,14 @@ static void log_locally(time_t now, char *msg, logFile_t *log_file)
 			close(log_file->fd);
 			goto reopen;
 		}
+	}
+	else if (log_file->fd == 1) {
+		/* We are logging to stdout: do nothing */
+	}
+	else {
+		if (LONE_DASH(log_file->path)) {
+			log_file->fd = 1;
+			/* log_file->isRegular = 0; - already is */
 		} else {
  reopen:
 			log_file->fd = open(log_file->path, O_WRONLY | O_CREAT
@@ -622,6 +632,7 @@ static void log_locally(time_t now, char *msg, logFile_t *log_file)
 			}
 #endif
 		}
+	}
 
 #ifdef SYSLOGD_WRLOCK
 	fl.l_whence = SEEK_SET;
@@ -865,7 +876,6 @@ static int try_to_resolve_remote(remoteHost_t *rh)
 static void do_syslogd(void) NORETURN;
 static void do_syslogd(void)
 {
-	int sock_fd;
 #if ENABLE_FEATURE_REMOTE_LOG
 	llist_t *item;
 #endif
@@ -886,7 +896,7 @@ static void do_syslogd(void)
 	signal(SIGALRM, do_mark);
 	alarm(G.markInterval);
 #endif
-	sock_fd = create_socket();
+	xmove_fd(create_socket(), STDIN_FILENO);
 
 	if (option_mask32 & OPT_circularlog)
 		ipcsyslog_init();
@@ -907,7 +917,7 @@ static void do_syslogd(void)
 			recvbuf = G.recvbuf;
 #endif
  read_again:
-		sz = read(sock_fd, recvbuf, MAX_READ - 1);
+		sz = read(STDIN_FILENO, recvbuf, MAX_READ - 1);
 		if (sz < 0) {
 			if (!bb_got_signal)
 				bb_perror_msg("read from %s", _PATH_LOG);
@@ -978,7 +988,6 @@ static void do_syslogd(void)
 	} /* while (!bb_got_signal) */
 
 	timestamp_and_log_internal("syslogd exiting");
-	puts("syslogd exiting");
 	remove_pidfile(CONFIG_PID_FILE_PATH "/syslogd.pid");
 	ipcsyslog_cleanup();
 	if (option_mask32 & OPT_kmsg)