agetty: keep c_iflags unmodified on --autologin

agetty sets c_iflags according to interaction with serial line in
get_logname(). For --autologin it does not read from the line, so we
have no clue how to set the flags.

The current behavior is to zeroize the flags.  Unfortunately, it seems
like bad idea, because the line may be already properly initialized by
kernel (or systemd, etc.).

The new behavior is not touch the flags on --autologin.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1252764
Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 17 insertions, 4 deletions

diff --git a/term-utils/agetty.8 b/term-utils/agetty.8
index fcb1fd5fe..5a480808d 100644
--- a/term-utils/agetty.8
+++ b/term-utils/agetty.8
@@ -93,6 +93,10 @@ Automatically log in the specified user without asking for a username or passwor
 Using this option causes an \fB\-f \fIusername\fR option and argument to be
 added to the \fB/bin/login\fP command line.  See \fB\-\-login\-options\fR, which
 can be used to modify this option's behavior.
+
+Note that \fB\-\-autologin\fP may affect the way how agetty initializes the
+serial line, because on auto-login agetty does not read from the line and it
+has no opportunity optimize the line setting.
 .TP
 \-c, \-\-noreset
 Do not reset terminal cflags (control modes).  See \fBtermios\fP(3) for more
diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index 844220401..e22600e28 100644
--- a/term-utils/agetty.c
+++ b/term-utils/agetty.c
@@ -1264,13 +1264,22 @@ static void termio_init(struct options *op, struct termios *tp)
 	 * later on.
 	 */
 
+	/* The defaul is set c_iflag in termio_final() according to chardata.
+	 * Unfortunately, the chardata are not set according to the serial line
+	 * if --autolog is enabled. In this case we do not read from the line
+	 * at all. The best what we can do in this case is to keep c_iflag
+	 * unmodified for --autolog.
+	 */
+	if (!op->autolog) {
 #ifdef IUTF8
-	tp->c_iflag = tp->c_iflag & IUTF8;
-	if (tp->c_iflag & IUTF8)
-		op->flags |= F_UTF8;
+		tp->c_iflag = tp->c_iflag & IUTF8;
+		if (tp->c_iflag & IUTF8)
+			op->flags |= F_UTF8;
 #else
-	tp->c_iflag = 0;
+		tp->c_iflag = 0;
 #endif
+	}
+
 	tp->c_lflag = 0;
 	tp->c_oflag &= OPOST | ONLCR;