Fix IXANY and restart after signal (e.g. ctrl-C) in n_tty line discipline

Fix two N_TTY line discipline issues related to resuming a stopped TTY
(typically done with ctrl-S):

1) Fix handling of character that resumes a stopped TTY (with IXANY)

With "stty ixany", the TTY line discipline would lose the first character
after the stop, so typing, for example, "hi^Sthere" resulted in "hihere"
(the 't' would cause the resume after ^S, but it would then be thrown away
rather than processed as an input character).  This was inconsistent with
the behavior of other Unix systems.

2) Fix interrupt signal (e.g. ctrl-C) behavior in stopped TTYs

With "stty -ixany" (often the default), interrupt signals were ignored
in a stopped TTY until the TTY was resumed with the start char (typically
ctrl-Q), which was inconsistent with the behavior of other Unix systems.
Signed-off-by: Joe Peterson <joe@skyrush.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/n_tty.c

@@ -695,17 +695,16 @@ static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 		return;
 	}
 	
-	if (tty->stopped && !tty->flow_stopped &&
-	    I_IXON(tty) && I_IXANY(tty)) {
-		start_tty(tty);
-		return;
-	}
-	
 	if (I_ISTRIP(tty))
 		c &= 0x7f;
 	if (I_IUCLC(tty) && L_IEXTEN(tty))
 		c=tolower(c);
 
+	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
+	    ((I_IXANY(tty) && c != START_CHAR(tty) && c != STOP_CHAR(tty)) ||
+	     c == INTR_CHAR(tty) || c == QUIT_CHAR(tty)))
+		start_tty(tty);
+
 	if (tty->closing) {
 		if (I_IXON(tty)) {
 			if (c == START_CHAR(tty))