We accidentally haven't been using $TMUX to work out the session for a while

and in fact it is less useful that using the client ttyname. So don't bother
and don't pass it from the client. If we need it in future it is in c->environ.

client.c

@@ -284,10 +284,6 @@ client_main(int argc, char **argv, int flags)
 			size += strlen(argv[i]) + 1;
 		data = xmalloc((sizeof *data) + size);
 
-		/* Fill in command line arguments. */
-		data->pid = environ_pid;
-		data->session_id = environ_session_id;
-
 		/* Prepare command for server. */
 		data->argc = argc;
 		if (cmd_pack_argv(argc, argv, (char*)(data + 1), size) != 0) {

cmd.c

@@ -313,7 +313,6 @@ cmd_print(struct cmd *cmd, char *buf, size_t len)
 struct session *
 cmd_current_session(struct cmd_q *cmdq, int prefer_unattached)
 {
-	struct msg_command_data	*data = cmdq->msgdata;
 	struct client		*c = cmdq->client;
 	struct session		*s;
 	struct sessionslist	 ss;
@@ -355,13 +354,6 @@ cmd_current_session(struct cmd_q *cmdq, int prefer_unattached)
 			return (s);
 	}
 
-	/* Use the session from the TMUX environment variable. */
-	if (data != NULL && data->pid == getpid() && data->session_id != -1) {
-		s = session_find_by_id(data->session_id);
-		if (s != NULL)
-			return (s);
-	}
-
 	return (cmd_choose_session(prefer_unattached));
 }
 

server-client.c

@@ -62,6 +62,8 @@ server_client_create(int fd)
 		fatal("gettimeofday failed");
 	memcpy(&c->activity_time, &c->creation_time, sizeof c->activity_time);
 
+	environ_init(&c->environ);
+
 	c->cmdq = cmdq_new(c);
 	c->cmdq->client_exit = 1;
 

tmux.c

@@ -48,11 +48,8 @@ time_t		 start_time;
 char		 socket_path[MAXPATHLEN];
 int		 login_shell;
 char		*environ_path;
-pid_t		 environ_pid = -1;
-int		 environ_session_id = -1;
 
 __dead void	 usage(void);
-void	 	 parseenvironment(void);
 char 		*makesocketpath(const char *);
 
 #ifndef HAVE___PROGNAME
@@ -127,23 +124,6 @@ areshell(const char *shell)
 	return (0);
 }
 
-void
-parseenvironment(void)
-{
-	char	*env, path[256];
-	long	 pid;
-	int	 id;
-
-	if ((env = getenv("TMUX")) == NULL)
-		return;
-
-	if (sscanf(env, "%255[^,],%ld,%d", path, &pid, &id) != 3)
-		return;
-	environ_path = xstrdup(path);
-	environ_pid = pid;
-	environ_session_id = id;
-}
-
 char *
 makesocketpath(const char *label)
 {
@@ -226,7 +206,9 @@ main(int argc, char **argv)
 {
 	struct passwd	*pw;
 	char		*s, *path, *label, *home, **var, tmp[MAXPATHLEN];
-	int	 	 opt, flags, quiet, keys;
+	char		 in[256];
+	long long	 pid;
+	int	 	 opt, flags, quiet, keys, session;
 
 #if defined(DEBUG) && defined(__OpenBSD__)
 	malloc_options = (char *) "AFGJPX";
@@ -357,11 +339,15 @@ main(int argc, char **argv)
 		}
 	}
 
+	/* Get path from environment. */
+	s = getenv("TMUX");
+	if (s != NULL && sscanf(s, "%255[^,],%lld,%d", in, &pid, &session) == 3)
+		environ_path = xstrdup(in);
+
 	/*
 	 * Figure out the socket path. If specified on the command-line with -S
 	 * or -L, use it, otherwise try $TMUX or assume -L default.
 	 */
-	parseenvironment();
 	if (path == NULL) {
 		/* If no -L, use the environment. */
 		if (label == NULL) {

tmux.h

@@ -457,9 +457,6 @@ enum msgtype {
  * Don't forget to bump PROTOCOL_VERSION if any of these change!
  */
 struct msg_command_data {
-	pid_t	pid;		/* from $TMUX or -1 */
-	int	session_id;	/* from $TMUX or -1 */
-
 	int	argc;
 }; /* followed by packed argv */
 
@@ -1401,8 +1398,6 @@ struct cmd_q {
 	void			 (*emptyfn)(struct cmd_q *);
 	void			*data;
 
-	struct msg_command_data	*msgdata;
-
 	TAILQ_ENTRY(cmd_q)       waitentry;
 };
 
@@ -1496,8 +1491,6 @@ extern time_t	 start_time;
 extern char	 socket_path[MAXPATHLEN];
 extern int	 login_shell;
 extern char	*environ_path;
-extern pid_t	 environ_pid;
-extern int	 environ_session_id;
 void		 logfile(const char *);
 const char	*getshell(void);
 int		 checkshell(const char *);