Have the client pass its stdin fd to the server when identifying itself and

have the server use that rather than reopening the tty. If the fd isn't given,
use the old behaviour (so no need for a version change).

This allows tmux to be used as the shell, so also change so that when working
out the command to execute if default-command is empty (the default), tmux will
try not execute itself.

client.c

@@ -119,7 +119,8 @@ server_started:
 		if (strlcpy(data.tty, name, sizeof data.tty) >= sizeof data.tty)
 			fatalx("ttyname failed");
 
-		client_write_server(cctx, MSG_IDENTIFY, &data, sizeof data);
+		imsg_compose(&cctx->ibuf, MSG_IDENTIFY,
+		    PROTOCOL_VERSION, -1, STDIN_FILENO, &data, sizeof data);
 	}
 
 	return (0);

server-msg.c

@@ -27,7 +27,7 @@
 #include "tmux.h"
 
 void	server_msg_command(struct client *, struct msg_command_data *);
-void	server_msg_identify(struct client *, struct msg_identify_data *);
+void	server_msg_identify(struct client *, struct msg_identify_data *, int);
 void	server_msg_resize(struct client *, struct msg_resize_data *);
 
 void printflike2 server_msg_command_error(struct cmd_ctx *, const char *, ...);
@@ -76,7 +76,7 @@ server_msg_dispatch(struct client *c)
 				fatalx("bad MSG_IDENTIFY size");
 			memcpy(&identifydata, imsg.data, sizeof identifydata);
 
-			server_msg_identify(c, &identifydata);
+			server_msg_identify(c, &identifydata, imsg.fd);
 			break;
 		case MSG_RESIZE:
 			if (datalen != sizeof resizedata)
@@ -235,7 +235,7 @@ error:
 }
 
 void
-server_msg_identify(struct client *c, struct msg_identify_data *data)
+server_msg_identify(struct client *c, struct msg_identify_data *data, int fd)
 {
 	c->tty.sx = data->sx;
 	c->tty.sy = data->sy;
@@ -247,7 +247,7 @@ server_msg_identify(struct client *c, struct msg_identify_data *data)
 
 	data->tty[(sizeof data->tty) - 1] = '\0';
 	data->term[(sizeof data->term) - 1] = '\0';
-	tty_init(&c->tty, data->tty, data->term);
+	tty_init(&c->tty, fd, data->tty, data->term);
 	if (data->flags & IDENTIFY_UTF8)
 		c->tty.flags |= TTY_UTF8;
 	if (data->flags & IDENTIFY_256COLOURS)

tmux.h

@@ -1158,7 +1158,7 @@ void	tty_putcode2(struct tty *, enum tty_code_code, int, int);
 void	tty_puts(struct tty *, const char *);
 void	tty_putc(struct tty *, u_char);
 void	tty_pututf8(struct tty *, const struct grid_utf8 *);
-void	tty_init(struct tty *, char *, char *);
+void	tty_init(struct tty *, int, char *, char *);
 void	tty_start_tty(struct tty *);
 void	tty_stop_tty(struct tty *);
 void	tty_detect_utf8(struct tty *);

tty.c

@@ -45,9 +45,11 @@ void	tty_cell(struct tty *,
     	    const struct grid_cell *, const struct grid_utf8 *);
 
 void
-tty_init(struct tty *tty, char *path, char *term)
+tty_init(struct tty *tty, int fd, char *path, char *term)
 {
 	tty->path = xstrdup(path);
+	tty->fd = fd;
+
 	if (term == NULL || *term == '\0')
 		tty->termname = xstrdup("unknown");
 	else
@@ -59,12 +61,14 @@ tty_init(struct tty *tty, char *path, char *term)
 int
 tty_open(struct tty *tty, const char *overrides, char **cause)
 {
-	int		 mode;
+	int	mode;
 
-	tty->fd = open(tty->path, O_RDWR|O_NONBLOCK);
 	if (tty->fd == -1) {
-		xasprintf(cause, "%s: %s", tty->path, strerror(errno));
-		return (-1);
+		tty->fd = open(tty->path, O_RDWR|O_NONBLOCK);
+		if (tty->fd == -1) {
+			xasprintf(cause, "%s: %s", tty->path, strerror(errno));
+			return (-1);
+		}
 	}
 
 	if ((mode = fcntl(tty->fd, F_GETFL)) == -1)

window.c

@@ -61,18 +61,29 @@ RB_GENERATE(winlinks, winlink, entry, winlink_cmp);
 const char *
 window_default_command(void)
 {
-	const char	*shell;
+	const char	*shell, *ptr;
 	struct passwd	*pw;
 
 	shell = getenv("SHELL");
 	if (shell != NULL && *shell != '\0')
-		return (shell);
+		goto found;
 
 	pw = getpwuid(getuid());
-	if (pw != NULL && pw->pw_shell != NULL && *pw->pw_shell != '\0')
-		return (pw->pw_shell);
+	if (pw != NULL && pw->pw_shell != NULL && *pw->pw_shell != '\0') {
+		shell = pw->pw_shell;
+		goto found;
+	}
 
 	return (_PATH_BSHELL);
+
+found:
+	if ((ptr = strrchr(shell, '/')) != NULL)
+		ptr++;
+	else
+		ptr = shell;
+	if (strcmp(ptr, __progname) == 0)
+		return (_PATH_BSHELL);
+	return (shell);
 }
 
 int