Properly set the low watermarks when reducing the baud rate.

Now that buffers are deallocated lazily, we should not use
tty*q_getsize() to obtain the buffer size to calculate the low
watermarks. Doing this may cause the watermark to be placed outside the
typical buffer size.

This caused some regressions after my previous commit to the TTY code,
which allows pseudo-devices to resize the buffers as well.

Reported by:	yongari, dougb
MFC after:	1 week

2 files changed, 16 insertions, 2 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index a3db944..81f6741 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -109,14 +109,14 @@ tty_watermarks(struct tty *tp)
 	ttyinq_setsize(&tp->t_inq, tp, bs);
 
 	/* Set low watermark at 10% (when 90% is available). */
-	tp->t_inlow = (ttyinq_getsize(&tp->t_inq) * 9) / 10;
+	tp->t_inlow = (ttyinq_getallocatedsize(&tp->t_inq) * 9) / 10;
 
 	/* Provide an ouput buffer for 0.2 seconds of data. */
 	bs = MIN(tp->t_termios.c_ospeed / 5, TTYBUF_MAX);
 	ttyoutq_setsize(&tp->t_outq, tp, bs);
 
 	/* Set low watermark at 10% (when 90% is available). */
-	tp->t_outlow = (ttyoutq_getsize(&tp->t_outq) * 9) / 10;
+	tp->t_outlow = (ttyoutq_getallocatedsize(&tp->t_outq) * 9) / 10;
 }
 
 static int
diff --git a/sys/sys/ttyqueue.h b/sys/sys/ttyqueue.h
index aac6b3c..2d1a565 100644
--- a/sys/sys/ttyqueue.h
+++ b/sys/sys/ttyqueue.h
@@ -93,6 +93,13 @@ ttyinq_getsize(struct ttyinq *ti)
 }
 
 static __inline size_t
+ttyinq_getallocatedsize(struct ttyinq *ti)
+{
+
+	return (ti->ti_quota * TTYINQ_DATASIZE);
+}
+
+static __inline size_t
 ttyinq_bytesleft(struct ttyinq *ti)
 {
 	size_t len;
@@ -143,6 +150,13 @@ ttyoutq_getsize(struct ttyoutq *to)
 }
 
 static __inline size_t
+ttyoutq_getallocatedsize(struct ttyoutq *to)
+{
+
+	return (to->to_quota * TTYOUTQ_DATASIZE);
+}
+
+static __inline size_t
 ttyoutq_bytesleft(struct ttyoutq *to)
 {
 	size_t len;