Re: Problem with gettimeofday

[Alexander Samilovskih <alexsamilovskih@xxxxxxxxx>]

Hi,

There are several places where gettimeofday should be replaced by
clock_gettime(CLOCK_MONOTONIC_RAW). According to manual pages
gettimeofday affected by discontinues jumps made by system
administrator, can be slewed by ntpd or kinda stuff. So when we
subtract two different timestamps from gettimeofday we can get
confusing results

sys-utils/eject.c
libmount/lock.c
maybe some other places...


diff --git a/include/timeutils.h b/include/timeutils.h
index bcae613..7cf972d 100644
--- a/include/timeutils.h
+++ b/include/timeutils.h
@@ -51,5 +51,6 @@ typedef uint64_t nsec_t;
 #define FORMAT_TIMESPAN_MAX 64

 int parse_timestamp(const char *t, usec_t *usec);
+int gettime_monotonic(struct timeval *tv);

 #endif /* UTIL_LINUX_TIME_UTIL_H */
diff --git a/lib/timeutils.c b/lib/timeutils.c
index 7fe6218..06ae597 100644
--- a/lib/timeutils.c
+++ b/lib/timeutils.c
@@ -336,3 +336,24 @@ int parse_timestamp(const char *t, usec_t *usec)

  return 0;
 }
+
+int gettime_monotonic(struct timeval *tv)
+{
+#ifdef CLOCK_MONOTONIC
+ //Can slew only by ntp and adjtime
+ int ret;
+ struct timespec ts;
+#ifdef CLOCK_MONOTONIC_RAW
+ //Linux specific, cant slew
+ if (!(ret = clock_gettime(CLOCK_MONOTONIC_RAW, &ts))) {
+#else
+ if (!(ret = clock_gettime(CLOCK_MONOTONIC, &ts))) {
+#endif
+ tv->tv_sec = ts.tv_sec;
+ tv->tv_usec = ts.tv_nsec / 1000;
+ }
+ return ret;
+#else
+ return gettimeofday(tv, NULL);
+#endif
+}
\ No newline at end of file


diff --git a/libmount/src/lock.c b/libmount/src/lock.c
index 8667db9..41f8ed1 100644
--- a/libmount/src/lock.c
+++ b/libmount/src/lock.c
@@ -25,6 +25,7 @@
 #include "closestream.h"
 #include "pathnames.h"
 #include "mountP.h"
+#include "timeutils.h"

 /*
  * lock handler
@@ -258,7 +259,7 @@ static int mnt_wait_mtab_lock(struct libmnt_lock
*ml, struct flock *fl, time_t m
  struct sigaction sa, osa;
  int ret = 0;

- gettimeofday(&now, NULL);
+ gettime_monotonic(&now);

  if (now.tv_sec >= maxtime)
  return 1; /* timeout */
@@ -408,7 +409,7 @@ static int lock_mtab(struct libmnt_lock *ml)
  }
  close(i);

- gettimeofday(&maxtime, NULL);
+ gettime_monotonic(&maxtime);
  maxtime.tv_sec += MOUNTLOCK_MAXTIME;

  waittime.tv_sec = 0;
@@ -434,7 +435,7 @@ static int lock_mtab(struct libmnt_lock *ml)
  if (ml->lockfile_fd < 0) {
  /* Strange... Maybe the file was just deleted? */
  int errsv = errno;
- gettimeofday(&now, NULL);
+ gettime_monotonic(&now);
  if (errsv == ENOENT && now.tv_sec < maxtime.tv_sec) {
  ml->locked = 0;
  continue;


diff --git a/sys-utils/eject.c b/sys-utils/eject.c
index 03744c7..049cdb7 100644
--- a/sys-utils/eject.c
+++ b/sys-utils/eject.c
@@ -52,6 +52,7 @@
 #include "xalloc.h"
 #include "pathnames.h"
 #include "sysfs.h"
+#include "timeutils.h"

 /*
  * sg_io_hdr_t driver_status -- see kernel include/scsi/scsi.h
@@ -460,7 +461,7 @@ static void toggle_tray(int fd)
  * needed.  In my experience the function needs less than 0.05
  * seconds if the tray was already open, and at least 1.5 seconds
  * if it was closed.  */
- gettimeofday(&time_start, NULL);
+ gettime_monotonic(&time_start);

  /* Send the CDROMEJECT command to the device. */
  if (!eject_cdrom(fd))
@@ -468,7 +469,7 @@ static void toggle_tray(int fd)

  /* Get the second timestamp, to measure the time needed to open
  * the tray.  */
- gettimeofday(&time_stop, NULL);
+ gettime_monotonic(&time_stop);

  time_elapsed = (time_stop.tv_sec * 1000000 + time_stop.tv_usec) -
  (time_start.tv_sec * 1000000 + time_start.tv_usec);
--
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