Allow the buffer size to be configured for pseudo-like TTY devices.

Devices that don't implement param() (which means they don't support
hardware parameters such as flow control, baud rate) hardcode the baud
rate to TTYDEF_SPEED. This means the buffer size cannot be configured,
which is a little inconvenient when using canonical mode with big lines
of input, etc.

Make it adjustable, but do clamp it between B50 and B115200 to prevent
awkward buffer sizes. Remove the baud rate assignment from
/etc/gettytab. Trust the kernel to fill in a proper value.

Reported by:	Mikolaj Golub <to my trociny gmail com>
MFC after:	1 month

2 files changed, 14 insertions, 3 deletions

diff --git a/etc/gettytab b/etc/gettytab
index b75da3d13816..2d3a80abc9be 100644
--- a/etc/gettytab
+++ b/etc/gettytab
@@ -162,7 +162,7 @@ X|Xwindow|X window system:\
 	:fd@:nd@:cd@:rw:sp#9600:
 
 P|Pc|Pc console:\
-	:ht:np:sp#115200:
+	:ht:np:
 
 #
 # Wierdo special case for fast crt's with hardcopy devices
diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 25908df8acc1..a3db944e7c44 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -870,8 +870,19 @@ static int
 ttydevsw_defparam(struct tty *tp, struct termios *t)
 {
 
-	/* Use a fake baud rate, we're not a real device. */
-	t->c_ispeed = t->c_ospeed = TTYDEF_SPEED;
+	/*
+	 * Allow the baud rate to be adjusted for pseudo-devices, but at
+	 * least restrict it to 115200 to prevent excessive buffer
+	 * usage.  Also disallow 0, to prevent foot shooting.
+	 */
+	if (t->c_ispeed < B50)
+		t->c_ispeed = B50;
+	else if (t->c_ispeed > B115200)
+		t->c_ispeed = B115200;
+	if (t->c_ospeed < B50)
+		t->c_ospeed = B50;
+	else if (t->c_ospeed > B115200)
+		t->c_ospeed = B115200;
 
 	return (0);
 }