1 files changed, 73 insertions, 19 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 640c9e871044..3afdd9033a9c 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -118,6 +118,9 @@ struct n_tty_data {
 	size_t read_tail;
 	size_t line_start;
 
+	/* # of chars looked ahead (to find software flow control chars) */
+	size_t lookahead_count;
+
 	/* protected by output lock */
 	unsigned int column;
 	unsigned int canon_column;
@@ -333,6 +336,8 @@ static void reset_buffer_flags(struct n_tty_data *ldata)
 	ldata->erasing = 0;
 	bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
 	ldata->push = 0;
+
+	ldata->lookahead_count = 0;
 }
 
 static void n_tty_packet_mode_flush(struct tty_struct *tty)
@@ -1225,12 +1230,30 @@ static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
 	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
 }
 
-/* Returns true if c is consumed as flow-control character */
-static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
+/**
+ * n_tty_receive_char_flow_ctrl - receive flow control chars
+ * @tty: terminal device
+ * @c: character
+ * @lookahead_done: lookahead has processed this character already
+ *
+ * Receive and process flow control character actions.
+ *
+ * In case lookahead for flow control chars already handled the character in
+ * advance to the normal receive, the actions are skipped during normal
+ * receive.
+ *
+ * Returns true if @c is consumed as flow-control character, the character
+ * must not be treated as normal character.
+ */
+static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c,
+					 bool lookahead_done)
 {
 	if (!n_tty_is_char_flow_ctrl(tty, c))
 		return false;
 
+	if (lookahead_done)
+		return true;
+
 	if (c == START_CHAR(tty)) {
 		start_tty(tty);
 		process_echoes(tty);
@@ -1242,11 +1265,12 @@ static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c
 	return true;
 }
 
-static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
+static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c,
+				       bool lookahead_done)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 
-	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c))
+	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done))
 		return;
 
 	if (L_ISIG(tty)) {
@@ -1401,7 +1425,8 @@ static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 	put_tty_queue(c, ldata);
 }
 
-static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c)
+static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c,
+				       bool lookahead_done)
 {
 	if (I_ISTRIP(tty))
 		c &= 0x7f;
@@ -1409,12 +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))
-			stop_tty(tty);
-		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);
 		}
@@ -1457,6 +1480,27 @@ n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
 		n_tty_receive_char_flagged(tty, c, flag);
 }
 
+/* Caller must ensure count > 0 */
+static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const unsigned char *cp,
+				      const unsigned char *fp, unsigned int count)
+{
+	struct n_tty_data *ldata = tty->disc_data;
+	unsigned char flag = TTY_NORMAL;
+
+	ldata->lookahead_count += count;
+
+	if (!I_IXON(tty))
+		return;
+
+	while (count--) {
+		if (fp)
+			flag = *fp++;
+		if (likely(flag == TTY_NORMAL))
+			n_tty_receive_char_flow_ctrl(tty, *cp, false);
+		cp++;
+	}
+}
+
 static void
 n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
 			   const char *fp, int count)
@@ -1496,7 +1540,7 @@ n_tty_receive_buf_raw(struct tty_struct *tty, const unsigned char *cp,
 
 static void
 n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
-			  const char *fp, int count)
+			  const char *fp, int count, bool lookahead_done)
 {
 	char flag = TTY_NORMAL;
 
@@ -1504,12 +1548,12 @@ n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
 		if (fp)
 			flag = *fp++;
 		if (likely(flag == TTY_NORMAL))
-			n_tty_receive_char_closing(tty, *cp++);
+			n_tty_receive_char_closing(tty, *cp++, lookahead_done);
 	}
 }
 
 static void n_tty_receive_buf_standard(struct tty_struct *tty,
-		const unsigned char *cp, const char *fp, int count)
+		const unsigned char *cp, const char *fp, int count, bool lookahead_done)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	char flag = TTY_NORMAL;
@@ -1540,7 +1584,7 @@ static void n_tty_receive_buf_standard(struct tty_struct *tty,
 		}
 
 		if (test_bit(c, ldata->char_map))
-			n_tty_receive_char_special(tty, c);
+			n_tty_receive_char_special(tty, c, lookahead_done);
 		else
 			n_tty_receive_char(tty, c);
 	}
@@ -1551,21 +1595,30 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
+	size_t la_count = min_t(size_t, ldata->lookahead_count, count);
 
 	if (ldata->real_raw)
 		n_tty_receive_buf_real_raw(tty, cp, fp, count);
 	else if (ldata->raw || (L_EXTPROC(tty) && !preops))
 		n_tty_receive_buf_raw(tty, cp, fp, count);
-	else if (tty->closing && !L_EXTPROC(tty))
-		n_tty_receive_buf_closing(tty, cp, fp, count);
-	else {
-		n_tty_receive_buf_standard(tty, cp, fp, count);
+	else if (tty->closing && !L_EXTPROC(tty)) {
+		if (la_count > 0)
+			n_tty_receive_buf_closing(tty, cp, fp, la_count, true);
+		if (count > la_count)
+			n_tty_receive_buf_closing(tty, cp, fp, count - la_count, false);
+	} else {
+		if (la_count > 0)
+			n_tty_receive_buf_standard(tty, cp, fp, la_count, true);
+		if (count > la_count)
+			n_tty_receive_buf_standard(tty, cp, fp, count - la_count, false);
 
 		flush_echoes(tty);
 		if (tty->ops->flush_chars)
 			tty->ops->flush_chars(tty);
 	}
 
+	ldata->lookahead_count -= la_count;
+
 	if (ldata->icanon && !L_EXTPROC(tty))
 		return;
 
@@ -2446,6 +2499,7 @@ static struct tty_ldisc_ops n_tty_ops = {
 	.receive_buf     = n_tty_receive_buf,
 	.write_wakeup    = n_tty_write_wakeup,
 	.receive_buf2	 = n_tty_receive_buf2,
+	.lookahead_buf	 = n_tty_lookahead_flow_ctrl,
 };
 
 /**