Even with TTYReset=no it seems with systemd or plymouth the termios
flags become changed from under the first agetty on a serial system
console as the flags are locked.

---
 agetty.c |   39 ++++++++++++++++++++++++++++++++-------
 1 file changed, 32 insertions(+), 7 deletions(-)

--- term-utils/agetty.c
+++ term-utils/agetty.c	2014-01-10 13:05:50.411075349 +0000
@@ -281,8 +281,9 @@ static void login_options_to_argv(char *
 static char *fakehost;
 
 #ifdef DEBUGGING
+# include "closestream.h"
 # ifndef DEBUG_OUTPUT
-#  define DEBUG_OUTPUT "/dev/ttyp0"
+#  define DEBUG_OUTPUT "/dev/tty10"
 # endif
 # define debug(s) do { fprintf(dbf,s); fflush(dbf); } while (0)
 FILE *dbf;
@@ -320,8 +321,12 @@ int main(int argc, char **argv)
 
 #ifdef DEBUGGING
 	dbf = fopen(DEBUG_OUTPUT, "w");
-	for (int i = 1; i < argc; i++)
+	for (int i = 1; i < argc; i++) {
+		if (i > 1)
+			debug(" ");
 		debug(argv[i]);
+	}
+	debug("\n");
 #endif				/* DEBUGGING */
 
 	/* Parse command-line arguments. */
@@ -473,7 +478,6 @@ int main(int argc, char **argv)
 	if (options.osrelease)
 		free(options.osrelease);
 #ifdef DEBUGGING
-	fprintf(dbf, "read %c\n", ch);
 	if (close_stream(dbf) != 0)
 		log_err("write failed: %s", DEBUG_OUTPUT);
 #endif
@@ -1090,6 +1094,25 @@ static void termio_init(struct options *
 {
 	speed_t ispeed, ospeed;
 	struct winsize ws;
+	struct termios lock;
+	int i;
+
+	for (i = 0; i < 20; i++) {
+		/*
+		 * Even with TTYReset=no it seems with systemd or plymouth
+		 * the termios flags become changed from under the first
+		 * agetty on a serial system console as the flags are locked.
+		 */
+		memset(&lock, 0, sizeof(struct termios));
+		if (ioctl(STDIN_FILENO, TIOCGLCKTRMIOS, &lock) < 0)
+			break;
+		if (!lock.c_iflag && !lock.c_oflag && !lock.c_cflag && !lock.c_lflag)
+			break;
+		debug("termios locked\n");
+		sleep(1);
+	}
+       memset(&lock, 0, sizeof(struct termios));
+       ioctl(STDIN_FILENO, TIOCSLCKTRMIOS, &lock);
 
 	if (op->flags & F_VCONSOLE) {
 #if defined(IUTF8) && defined(KDGKBMODE)
@@ -1154,9 +1177,6 @@ static void termio_init(struct options *
 	 * later on.
 	 */
 
-	 /* Flush input and output queues, important for modems! */
-	tcflush(STDIN_FILENO, TCIOFLUSH);
-
 #ifdef IUTF8
 	tp->c_iflag = tp->c_iflag & IUTF8;
 	if (tp->c_iflag & IUTF8)
@@ -1216,8 +1236,11 @@ static void termio_init(struct options *
 	if (op->flags & F_RTSCTS)
 		tp->c_cflag |= CRTSCTS;
 #endif
+	 /* Flush input and output queues, important for modems! */
+	tcflush(STDIN_FILENO, TCIOFLUSH);
 
-	tcsetattr(STDIN_FILENO, TCSANOW, tp);
+	if (tcsetattr(STDIN_FILENO, TCSANOW, tp))
+		log_warn(_("setting terminal attributes failed: %m"));
 
 	/* Go to blocking input even in local mode. */
 	fcntl(STDIN_FILENO, F_SETFL,
@@ -1238,6 +1261,10 @@ static void reset_vc(const struct option
 
 	if (tcsetattr(STDIN_FILENO, TCSADRAIN, tp))
 		log_warn(_("setting terminal attributes failed: %m"));
+
+	/* Go to blocking input even in local mode. */
+	fcntl(STDIN_FILENO, F_SETFL,
+	      fcntl(STDIN_FILENO, F_GETFL, 0) & ~O_NONBLOCK);
 }
 
 /* Extract baud rate from modem status message. */