rtcwake: wait stdin to settle down before entering a system sleep

This can delay entering to system sleep up to 0.28 seconds while discarding
input, when stdin is interactive device.

[kzak@redhat.com: - add note to the man page]

Reference: https://github.com/karelzak/util-linux/issues/527
See-also: a85c39013491713ac0d9e24fd0f07b4fabdcfc17
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 25 insertions, 2 deletions

diff --git a/sys-utils/rtcwake.8.in b/sys-utils/rtcwake.8.in
index b35860113..72eb0e34f 100644
--- a/sys-utils/rtcwake.8.in
+++ b/sys-utils/rtcwake.8.in
@@ -48,8 +48,11 @@ an alarm up to 24 hours in the future.
 .PP
 The suspend setup maybe be interrupted by active hardware; for example wireless USB
 input devices that continue to send events for some fraction of a second after the
-return key is pressed. In this case is better to use sleep command before invoking
-suspend by rtcwake.
+return key is pressed.
+.BR rtcwake
+tries to avoid this problem and it waits to terminal to settle down before
+entering a system sleep.
+
 .SH OPTIONS
 .TP
 .BR \-A , " \-\-adjfile " \fIfile
diff --git a/sys-utils/rtcwake.c b/sys-utils/rtcwake.c
index 20e40a07f..b63c64627 100644
--- a/sys-utils/rtcwake.c
+++ b/sys-utils/rtcwake.c
@@ -23,12 +23,14 @@
 #include <fcntl.h>
 #include <getopt.h>
 #include <linux/rtc.h>
+#include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/time.h>
 #include <sys/types.h>
+#include <termios.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -260,6 +262,22 @@ nothing:
 	return NULL;
 }
 
+static void wait_stdin(struct rtcwake_control *ctl)
+{
+	struct pollfd fd[] = {
+		{.fd = STDIN_FILENO, .events = POLLIN}
+	};
+	int tries = 0;
+
+	while (tries < 8 && poll(fd, 1, 10) == 1) {
+		if (ctl->verbose)
+			warnx(_("discarding stdin"));
+		xusleep(250000);
+		tcflush(STDIN_FILENO, TCIFLUSH);
+		tries++;
+	}
+}
+
 static void suspend_system(struct rtcwake_control *ctl)
 {
 	FILE	*f = fopen(SYS_POWER_STATE_PATH, "w");
@@ -270,6 +288,8 @@ static void suspend_system(struct rtcwake_control *ctl)
 	}
 
 	if (!ctl->dryrun) {
+		if (isatty(STDIN_FILENO))
+			wait_stdin(ctl);
 		fprintf(f, "%s\n", ctl->mode_str);
 		fflush(f);
 	}