From 9bf622dad9650e8bcc02d17b9e627d6aa061d163 Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Mon, 1 Jun 2020 22:21:34 +0300
Subject: [PATCH] dmesg: adjust timestamps according to suspended time

Timestamps in kernel log comes from monotonic clocksource which does not
tick when system suspended. Suspended time easily sums into hours and days
rendering human readable timestamps in dmesg useless.

Adjusting timestamps accouring to current delta between boottime and
monotonic clocksources produces accurate timestamps for messages printed
since last resume. Which are supposed to be most interesting.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 include/monotonic.h |  2 ++
 lib/monotonic.c     | 12 ++++++++++++
 sys-utils/dmesg.1   |  2 ++
 sys-utils/dmesg.c   | 22 +++++++++++++++++-----
 4 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/monotonic.h b/include/monotonic.h
index 7a69d9e4b..380e59c37 100644
--- a/include/monotonic.h
+++ b/include/monotonic.h
@@ -15,6 +15,8 @@
 
 extern int get_boot_time(struct timeval *boot_time);
 
+extern time_t get_suspended_time(void);
+
 extern int gettime_monotonic(struct timeval *tv);
 
 #endif /* UTIL_LINUX_MONOTONIC_H */
diff --git a/lib/monotonic.c b/lib/monotonic.c
index b684d8dd6..f0aeba682 100644
--- a/lib/monotonic.c
+++ b/lib/monotonic.c
@@ -48,6 +48,18 @@ int get_boot_time(struct timeval *boot_time)
 #endif
 }
 
+time_t get_suspended_time(void)
+{
+#if defined(CLOCK_BOOTTIME) && defined(CLOCK_MONOTONIC)
+	struct timespec boot, mono;
+
+	if (clock_gettime(CLOCK_BOOTTIME, &boot) == 0 &&
+	    clock_gettime(CLOCK_MONOTONIC, &mono) == 0)
+		return boot.tv_sec - mono.tv_sec;
+#endif
+	return 0;
+}
+
 int gettime_monotonic(struct timeval *tv)
 {
 #ifdef CLOCK_MONOTONIC
diff --git a/sys-utils/dmesg.1 b/sys-utils/dmesg.1
index 61a6ce894..6c5773a6b 100644
--- a/sys-utils/dmesg.1
+++ b/sys-utils/dmesg.1
@@ -161,6 +161,8 @@ source used for the logs is
 .B not updated after
 system
 .BR SUSPEND / RESUME .
+Timestamps are adjusted according to current delta between boottime and monotonic
+clocks, this works only for messages printed after last resume.
 .IP "\fB\-t\fR, \fB\-\-notime\fR"
 Do not print kernel's timestamps.
 .IP "\fB\-\-time\-format\fR \fIformat\fR"
diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index ae1ebc74a..c78f01ca8 100644
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -169,6 +169,7 @@ struct dmesg_control {
 	struct timeval	lasttime;	/* last printed timestamp */
 	struct tm	lasttm;		/* last localtime */
 	struct timeval	boot_time;	/* system boot time */
+	time_t		suspended_time;	/* time spent in suspeneded state */
 
 	int		action;		/* SYSLOG_ACTION_* */
 	int		method;		/* DMESG_METHOD_* */
@@ -824,7 +825,7 @@ static struct tm *record_localtime(struct dmesg_control *ctl,
 				   struct dmesg_record *rec,
 				   struct tm *tm)
 {
-	time_t t = ctl->boot_time.tv_sec + rec->tv.tv_sec;
+	time_t t = ctl->boot_time.tv_sec + ctl->suspended_time + rec->tv.tv_sec;
 	return localtime_r(&t, tm);
 }
 
@@ -852,7 +853,7 @@ static char *iso_8601_time(struct dmesg_control *ctl, struct dmesg_record *rec,
 			   char *buf, size_t bufsz)
 {
 	struct timeval tv = {
-		.tv_sec = ctl->boot_time.tv_sec + rec->tv.tv_sec,
+		.tv_sec = ctl->boot_time.tv_sec + ctl->suspended_time + rec->tv.tv_sec,
 		.tv_usec = rec->tv.tv_usec
 	};
 
@@ -1301,8 +1302,16 @@ static inline int dmesg_get_boot_time(struct timeval *tv)
 
 	return get_boot_time(tv);
 }
+
+static inline time_t dmesg_get_suspended_time(void)
+{
+	if (getenv("DMESG_TEST_BOOTIME"))
+		return 0;
+	return get_suspended_time();
+}
 #else
 # define dmesg_get_boot_time	get_boot_time
+# define dmesg_get_suspended_time	get_suspended_time
 #endif
 
 int main(int argc, char *argv[])
@@ -1499,9 +1508,12 @@ int main(int argc, char *argv[])
 
 	if ((is_timefmt(&ctl, RELTIME) ||
 	     is_timefmt(&ctl, CTIME)   ||
-	     is_timefmt(&ctl, ISO8601))
-	    && dmesg_get_boot_time(&ctl.boot_time) != 0)
-		ctl.time_fmt = DMESG_TIMEFTM_NONE;
+	     is_timefmt(&ctl, ISO8601))) {
+		if (dmesg_get_boot_time(&ctl.boot_time) != 0)
+			ctl.time_fmt = DMESG_TIMEFTM_NONE;
+		else
+			ctl.suspended_time = dmesg_get_suspended_time();
+	}
 
 	if (delta)
 		switch (ctl.time_fmt) {