linux-kernel - [PATCH v5 2/2] tty: Use flow-control char function on closing path

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Date:   Mon,  6 Jun 2022 16:32:15 +0300
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH v5 2/2] tty: Use flow-control char function on closing path

Use n_tty_receive_char_flow_ctrl also on the closing path. This makes
the code cleaner and consistent.

However, there a small change of regression!

The earlier closing path has a small difference compared with the
normal receive path. If START_CHAR and STOP_CHAR are equal, their
precedence is different depending on which path a character is
processed. I don't know whether this difference was intentional or
not, and if equal START_CHAR and STOP_CHAR is actually used anywhere.
But it feels not so useful corner case.

While this change would logically belong to those earlier changes,
having a separate patch for this is useful. If this regresses, bisect
can pinpoint this change rather than the large patch. Also, this
change is not necessary to minimal fix for the issue addressed in
the previous patch.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/tty/n_tty.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 917b5970b2e0..ea4dc316eafb 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1434,15 +1434,10 @@ static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c,
 		c = tolower(c);

 	if (I_IXON(tty)) {
-		if (c == STOP_CHAR(tty)) {
-			if (!lookahead_done)
-				stop_tty(tty);
-		} else if (c == START_CHAR(tty) && lookahead_done) {
-			return;
-		} else if (c == START_CHAR(tty) ||
-			 (tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
-			  c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
-			  c != SUSP_CHAR(tty))) {
+		if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
+		    tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
+		    c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
+		    c != SUSP_CHAR(tty)) {
 			start_tty(tty);
 			process_echoes(tty);
 		}
-- 
2.30.2