[PATCH] getty: Wait until all output written to stdout has been transmitted

Peter Korsgaard jacmet at sunsite.dk
Sun Jan 23 20:43:57 UTC 2011

>>>>> "Denys" == Denys Vlasenko <vda.linux at googlemail.com> writes:

 >>>>  DV> I propose adding sleep(1) before the flush.  Can you verify that it
 >>>>  DV> works?
 >>>> alarm+tcdrain maybe? This way it won't wait a second if there is nothing
 >>>> to drain.
 >>> Indeed this is a much better solution. Calling sleep(1) is really
 >>> annoying.
 >> Give me what I should test and I will do it.

 Denys> Insert sleep(1) before tcflush(0, TCIOFLUSH) in termios_init in getty.c,
 Denys> and let us know whether the "getty nukes a few last output chars sent
 Denys> before it is started" problem has been fixed by it.

 Denys> If it does, experiment with smaller sleeps - use usleep(MICROSECONDS) -
 Denys> and let us know what minimal pause is enough. Also let us know
 Denys> the settings on the serial line (primarily baud rate). If you can use
 Denys> different ones, experiment with smallest available.

The needed delay (obviously) depends on baudrate and amount of data in
the buffer, so it's impossible to come up with a delay that would fit
everyone while still not delaying more than needed.

Why not use the alarm() approach like suggested? E.G. something like

diff --git a/loginutils/getty.c b/loginutils/getty.c
index 015f077..d817d5d 100644
--- a/loginutils/getty.c
+++ b/loginutils/getty.c
@@ -276,9 +276,11 @@ static void open_tty(const char *tty)
 /* termios_init - initialize termios settings */
 static void termios_init(struct termios *tp, int speed)
-	/* Flush input and output queues, important for modems! */
-	/* TODO: sleep(1)? Users report lost chars, and I hesitate
-	 * to use tcdrain here instead of tcflush */
+	/* Wait up to 5 seconds for the output buffer to drain */
+	signal(SIGALRM, record_signo);
+	alarm(5);
+	tcdrain(0);
+	alarm(0);
 	tcflush(0, TCIOFLUSH);
 	/* Set speed if it wasn't specified as "0" on command line. */

This adds around 40 bytes.
Bye, Peter Korsgaard

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