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From: Ed Schouten <ed@FreeBSD.org>
Date: Tue, 1 Dec 2009 19:14:57 +0000 (UTC)
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Subject: svn commit: r199998 - head/sys/kern
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Author: ed
Date: Tue Dec  1 19:14:57 2009
New Revision: 199998
URL: http://svn.freebsd.org/changeset/base/199998

Log:
  Don't allocate an input buffer for a TTY when the receiver is turned off.
  
  When the termios CREAD flag is not set, it makes little sense to
  allocate an input buffer. Just set the size to 0 in this case to reduce
  memory footprint.
  
  Disallow CREAD to be disabled for pseudo-devices to prevent
  foot-shooting.

Modified:
  head/sys/kern/tty.c

Modified: head/sys/kern/tty.c
==============================================================================
--- head/sys/kern/tty.c	Tue Dec  1 17:29:25 2009	(r199997)
+++ head/sys/kern/tty.c	Tue Dec  1 19:14:57 2009	(r199998)
@@ -102,10 +102,11 @@ static const char	*dev_console_filename;
 static void
 tty_watermarks(struct tty *tp)
 {
-	size_t bs;
+	size_t bs = 0;
 
 	/* Provide an input buffer for 0.2 seconds of data. */
-	bs = MIN(tp->t_termios.c_ispeed / 5, TTYBUF_MAX);
+	if (tp->t_termios.c_cflag & CREAD)
+		bs = MIN(tp->t_termios.c_ispeed / 5, TTYBUF_MAX);
 	ttyinq_setsize(&tp->t_inq, tp, bs);
 
 	/* Set low watermark at 10% (when 90% is available). */
@@ -890,6 +891,7 @@ ttydevsw_defparam(struct tty *tp, struct
 		t->c_ospeed = B50;
 	else if (t->c_ospeed > B115200)
 		t->c_ospeed = B115200;
+	t->c_cflag |= CREAD;
 
 	return (0);
 }