Change tty default baud rate: 38400 -> 0, i.e. keep kernel default

This is a more sane default, and also what systems expect, and what
other getty implementations support.  I.e., unless specified, or set
to 0, the tty baud rate is zero -- which means do not change speed
at all.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

docs/config.md

@@ -301,8 +301,9 @@ Syntax
   `tty [LVLS] <CMD> <ARGS> [noclear] [nowait]`  
   The first variant of this option uses the built-in getty on the given
   TTY device DEV, in the given runlevels.  The DEV may be the special
-  keyword `@console`, which is very useful on embedded systems.  Default
+  keyword `@console`, or `console`, useful on embedded systems.
-  baud rate is `38400`.
+
+  The default baud rate is 0, i.e., keep kernel default.
 
   **Example:**
 ```conf
@@ -340,11 +341,12 @@ Syntax
   Embedded systems may want to enable automatic `DEV` by supplying the
   special `@console` device.  This works regardless weather the system
   uses `ttyS0`, `ttyAMA0`, `ttyMXC0`, or anything else.  Finit figures
-  it out by querying sysfs: `/sys/class/tty/console/active`.
+  it out by querying sysfs: `/sys/class/tty/console/active`.  The speed
+  can be omitted to keep the kernel default.
 
   **Example:**
 ```conf
-        tty [12345] @console 115200 noclear vt220
+        tty [12345] @console noclear vt220
 ```
 
   On really bare bones systems Finit offers a fallback shell, which

src/exec.c

@@ -369,15 +369,12 @@ pid_t run_getty(char *tty, char *baud, char *term, int noclear, int nowait, stru
 
 	pid = fork();
 	if (!pid) {
-		speed_t speed = B38400;
+		speed_t speed;
-
-		if (baud && baud[0]) {
-			speed = stty_parse_speed(baud);
-			if (B0 == speed)
-				logit(LOG_CRIT, "TTY %s: Invalid speed %s", tty, baud);
-		}
 
+		speed = stty_parse_speed(baud);
+		logit(LOG_INFO, "Starting built-in getty on %s, speed %u", tty, speed);
 		prepare_tty(tty, speed, "tty", rlimit);
+
 		if (activate_console(noclear, nowait))
 			_exit(getty(tty, speed, term, NULL));
 	}
@@ -415,6 +412,7 @@ pid_t run_getty2(char *tty, char *cmd, char *args[], int noclear, int nowait, st
 		dup2(fd, STDERR_FILENO);
 
 		/* Dunno speed, tell stty() to not mess with it */
+		logit(LOG_INFO, "Starting external getty on %s, speed %u", tty, B0);
 		prepare_tty(tty, B0, "getty", rlimit);
 
 		if (ioctl(STDIN_FILENO, TIOCSCTTY, 1) < 0)

src/stty.c

@@ -27,6 +27,7 @@
 #include <sys/ttydefaults.h>  /* Not included by default in musl libc */
 #include <termios.h>
 
+/* B0 means; keep kernel default */
 speed_t stty_parse_speed(char *baud)
 {
 	char *ptr;
@@ -66,6 +67,9 @@ speed_t stty_parse_speed(char *baud)
 		{ 4000000, B4000000 },
 	};
 
+	if (!baud || !baud[0])
+		return B0;
+
 	errno = 0;
 	val = strtoul(baud, &ptr, 10);
 	if (errno || ptr == baud)