linux-kernel - [PATCH 03/18] tty: Simplify tty buffer/ldisc interface with helper function

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Date:	Tue, 19 Mar 2013 16:21:38 -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 03/18] tty: Simplify tty buffer/ldisc interface with helper function

Ldisc interface functions must be called with interrupts enabled.
Separating the ldisc calls into a helper function simplies the
spin lock management.

Update the buffer's read index _after_ the data has been received
by the ldisc.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_buffer.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 6aa40f0..77e8115 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -403,6 +403,19 @@ int tty_prepare_flip_string_flags(struct tty_port *port,
 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
 
 
+static int receive_buf(struct tty_struct *tty, const unsigned char *char_buf,
+		       char *flag_buf, int count)
+{
+	struct tty_ldisc *disc = tty->ldisc;
+
+	if (disc->ops->receive_room)
+		tty->receive_room = disc->ops->receive_room(tty);
+	if (count > tty->receive_room)
+		count = tty->receive_room;
+	if (count)
+		disc->ops->receive_buf(tty, char_buf, flag_buf, count);
+	return count;
+}
 
 /**
  *	flush_to_ldisc
@@ -454,19 +467,16 @@ static void flush_to_ldisc(struct work_struct *work)
 			   line discipline as we want to empty the queue */
 			if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
 				break;
-			if (disc->ops->receive_room)
-				tty->receive_room = disc->ops->receive_room(tty);
-			if (!tty->receive_room)
-				break;
-			if (count > tty->receive_room)
-				count = tty->receive_room;
 			char_buf = head->char_buf_ptr + head->read;
 			flag_buf = head->flag_buf_ptr + head->read;
-			head->read += count;
 			spin_unlock_irqrestore(&buf->lock, flags);
-			disc->ops->receive_buf(tty, char_buf,
-							flag_buf, count);
+
+			count = receive_buf(tty, char_buf, flag_buf, count);
+
 			spin_lock_irqsave(&buf->lock, flags);
+			if (!count)
+				break;
+			head->read += count;
 		}
 		clear_bit(TTYP_FLUSHING, &port->iflags);
 	}
-- 
1.8.1.2

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