linux-kernel - [PATCH 06/18] n_tty: Split n_tty_chars_in

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Date:	Tue, 19 Mar 2013 16:21:41 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>
Cc:	Min Zhang <mzhang@...sta.com>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 06/18] n_tty: Split n_tty_chars_in_buffer() for reader-only interface

N_TTY .chars_in_buffer() method requires serialized access if
the current thread is not the single-consumer, n_tty_read().

Separate the internal interface; prepare for lockless read-side.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/n_tty.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 2cc3be0..51b08d9 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -299,7 +299,7 @@ static void n_tty_flush_buffer(struct tty_struct *tty)
  *	Locking: read_lock
  */
 
-static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
+static ssize_t chars_in_buffer(struct tty_struct *tty)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	unsigned long flags;
@@ -317,6 +317,11 @@ static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
 	return n;
 }
 
+static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
+{
+	return chars_in_buffer(tty);
+}
+
 /**
  *	is_utf8_continuation	-	utf8 multibyte check
  *	@c: byte to check
@@ -2030,7 +2035,7 @@ do_it_again:
 		}
 
 		/* If there is enough space in the read buffer now, let the
-		 * low-level driver know. We use n_tty_chars_in_buffer() to
+		 * low-level driver know. We use chars_in_buffer() to
 		 * check the buffer, as it now knows about canonical mode.
 		 * Otherwise, if the driver is throttled and the line is
 		 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
@@ -2038,7 +2043,7 @@ do_it_again:
 		 */
 		while (1) {
 			tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
-			if (n_tty_chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
+			if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
 				break;
 			if (!tty->count)
 				break;
-- 
1.8.1.2

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