Test if the mtime changes after fsync() has been called

fsync-mtime.c

/* Test if the mtime changes after fsync() has been called
 *
 * Bug originally reported at
 * http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19607
 *
 * Compile with:
 * gcc fsync-mtime.c -o fsync-mtime
 */

#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>

int
main (void)
{
  char const *filename = "test.txt";
  int fd = open(filename, O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666);
  if (fd < 0)
    return perror ("open"), 1;
  static char const message[] = "This is a test.\n";
  int messagelen = sizeof message - 1;
  if (write (fd, message, messagelen) != messagelen)
    return perror ("write"), 1;
  if (fsync (fd) != 0)
    return perror ("fsync"), 1;
  struct stat st1, st2;
  if (fstat (fd, &st1) != 0)
    return perror ("fstat"), 1;
  if (close (fd) != 0)
    return perror ("close"), 1;
  sleep (2);
  if (stat (filename, &st2) != 0)
    return perror ("stat"), 1;
  if (! (st1.st_mtim.tv_sec == st2.st_mtim.tv_sec
	 && st1.st_mtim.tv_nsec == st2.st_mtim.tv_nsec))
    {
      printf ("stat #1: %ld.%09ld\n", st1.st_mtim.tv_sec, st1.st_mtim.tv_nsec);
      printf ("stat #2: %ld.%09ld\n", st2.st_mtim.tv_sec, st2.st_mtim.tv_nsec);
      printf ("last-modified times do not conform to:\n"
	      "http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_08\n");
      return 1;
    }
  return 0;
}