Support SIGUSR2 to stop and start logging for an existing server. Also

we currently only have two log levels so just use -v and -vv rather than
-v and -vvvv, and clarify the man page entry for -v.

log.c

@@ -62,12 +62,10 @@ log_open(const char *name)
 
 	if (log_level == 0)
 		return;
-
-	if (log_file != NULL)
-		fclose(log_file);
+	log_close();
 
 	xasprintf(&path, "tmux-%s-%ld.log", name, (long)getpid());
-	log_file = fopen(path, "w");
+	log_file = fopen(path, "a");
 	free(path);
 	if (log_file == NULL)
 		return;
@@ -76,6 +74,21 @@ log_open(const char *name)
 	event_set_log_callback(log_event_cb);
 }
 
+/* Toggle logging. */
+void
+log_toggle(const char *name)
+{
+	if (log_level == 0) {
+		log_level = 1;
+		log_open(name);
+		log_debug("log opened");
+	} else {
+		log_debug("log closed");
+		log_level = 0;
+		log_close();
+	}
+}
+
 /* Close logging. */
 void
 log_close(void)

proc.c

@@ -265,3 +265,9 @@ proc_kill_peer(struct tmuxpeer *peer)
 {
 	peer->flags |= PEER_BAD;
 }
+
+void
+proc_toggle_log(struct tmuxproc *tp)
+{
+	log_toggle(tp->name);
+}

server.c

@@ -151,7 +151,7 @@ server_start(struct event_base *base, int lockfd, char *lockfile)
 	}
 	close(pair[0]);
 
-	if (log_get_level() > 3)
+	if (log_get_level() > 1)
 		tty_create_log();
 	if (pledge("stdio rpath wpath cpath fattr unix getpw recvfd proc exec "
 	    "tty ps", NULL) != 0)
@@ -365,6 +365,9 @@ server_signal(int sig)
 		}
 		server_add_accept(0);
 		break;
+	case SIGUSR2:
+		proc_toggle_log(server_proc);
+		break;
 	}
 }
 

signal.c

@@ -29,6 +29,7 @@ static struct event	ev_sigchld;
 static struct event	ev_sigcont;
 static struct event	ev_sigterm;
 static struct event	ev_sigusr1;
+static struct event	ev_sigusr2;
 static struct event	ev_sigwinch;
 
 void
@@ -59,6 +60,8 @@ set_signals(void (*handler)(int, short, void *), void *arg)
 	signal_add(&ev_sigterm, NULL);
 	signal_set(&ev_sigusr1, SIGUSR1, handler, arg);
 	signal_add(&ev_sigusr1, NULL);
+	signal_set(&ev_sigusr2, SIGUSR2, handler, arg);
+	signal_add(&ev_sigusr2, NULL);
 	signal_set(&ev_sigwinch, SIGWINCH, handler, arg);
 	signal_add(&ev_sigwinch, NULL);
 }
@@ -92,6 +95,8 @@ clear_signals(int after_fork)
 			fatal("sigaction failed");
 		if (sigaction(SIGUSR1, &sigact, NULL) != 0)
 			fatal("sigaction failed");
+		if (sigaction(SIGUSR2, &sigact, NULL) != 0)
+			fatal("sigaction failed");
 		if (sigaction(SIGWINCH, &sigact, NULL) != 0)
 			fatal("sigaction failed");
 	} else {
@@ -100,6 +105,7 @@ clear_signals(int after_fork)
 		event_del(&ev_sigcont);
 		event_del(&ev_sigterm);
 		event_del(&ev_sigusr1);
+		event_del(&ev_sigusr2);
 		event_del(&ev_sigwinch);
 	}
 }

tmux.1

@@ -199,7 +199,6 @@ characters to the terminal it is running (if not, they are replaced by
 .Ql _ ) .
 .It Fl v
 Request verbose logging.
-This option may be specified multiple times for increasing verbosity.
 Log messages will be saved into
 .Pa tmux-client-PID.log
 and
@@ -207,6 +206,22 @@ and
 files in the current directory, where
 .Em PID
 is the PID of the server or client process.
+.Pp
+If
+.Fl v
+is specified twice, an additional
+.Pa tmux-out-PID.log
+file is generated with a copy of everything
+.Nm
+writes to the terminal.
+.Pp
+The
+.Dv SIGUSR2
+signal may be sent to the
+.Nm
+server process to toggle logging between on (as if
+.Fl v
+was given) and off.
 .It Ar command Op Ar flags
 This specifies one of a set of commands used to control
 .Nm ,

tmux.h

@@ -1493,6 +1493,7 @@ struct tmuxpeer *proc_add_peer(struct tmuxproc *, int,
 	    void (*)(struct imsg *, void *), void *);
 void	proc_remove_peer(struct tmuxpeer *);
 void	proc_kill_peer(struct tmuxpeer *);
+void	proc_toggle_log(struct tmuxproc *);
 
 /* cfg.c */
 extern int cfg_finished;
@@ -2336,6 +2337,7 @@ char   *get_proc_name(int, char *);
 void	log_add_level(void);
 int	log_get_level(void);
 void	log_open(const char *);
+void	log_toggle(const char *);
 void	log_close(void);
 void printflike(1, 2) log_debug(const char *, ...);
 __dead void printflike(1, 2) fatal(const char *, ...);