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* utimensat fails to update ctime
@ 2009-12-18  5:38 Eric Blake
  2009-12-21  7:31 ` OGAWA Hirofumi
  0 siblings, 1 reply; 25+ messages in thread
From: Eric Blake @ 2009-12-18  5:38 UTC (permalink / raw)
  To: Linux Kernel Mailing List

POSIX requires that utimensat/futimens must update ctime in all cases
where any change is made (it only exempts when both atime and mtime were
requested as UTIME_OMIT, where the file must exist but no change is made).
 Unfortunately, when atime is specified and mtime is UTIME_OMIT, the
kernel mistakenly behaves like read(), by updating atime but not ctime.
This in turn caused a regression in coreutils 8.2, visible through 'touch -a':
http://lists.gnu.org/archive/html/bug-coreutils/2009-12/msg00171.html

Here is a simple program demonstrating the failure:
$ cat foo.c
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
int
main ()
{
  int fd = creat ("file", 0600);
  struct stat st1, st2;
  struct timespec t[2] = { { 1000000000, 0 }, { 0, UTIME_OMIT } };
  fstat (fd, &st1);
  sleep (1);
  futimens (fd, t);
  fstat (fd, &st2);
  return st1.st_ctime == st2.st_ctime;
}
$ gcc -o foo foo.c -D_GNU_SOURCE
$ ./foo; echo $?
1

The exit status should have been 0.

GNU coreutils will end up working around the bug by calling fstat/[l]stat
prior to futimens/utimensat, and populating the mtime field with the
desired value rather than using UTIME_OMIT.  But this is a pointless stat
call, which could be avoided if the kernel were fixed to comply with POSIX
by updating ctime even when mtime is UTIME_OMIT.

-- 
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9@byu.net

^ permalink raw reply	[flat|nested] 25+ messages in thread

end of thread, other threads:[~2009-12-24  0:49 UTC | newest]

Thread overview: 25+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2009-12-18  5:38 utimensat fails to update ctime Eric Blake
2009-12-21  7:31 ` OGAWA Hirofumi
2009-12-21 13:12   ` Eric Blake
2009-12-21 13:39     ` Eric Blake
2009-12-21 15:05       ` OGAWA Hirofumi
2009-12-22  4:37         ` Eric Blake
2009-12-22  9:00           ` OGAWA Hirofumi
2009-12-22  9:56             ` [fuse-devel] " Jean-Pierre André
2009-12-22 10:43               ` OGAWA Hirofumi
2009-12-22 12:07                 ` Jean-Pierre André
2009-12-22 13:00                   ` Miklos Szeredi
2009-12-22 13:30                   ` OGAWA Hirofumi
2009-12-22 16:16                     ` Jean-Pierre André
2009-12-22 17:58                       ` OGAWA Hirofumi
2009-12-23  9:43                         ` Jean-Pierre André
2009-12-23 11:08                           ` OGAWA Hirofumi
2009-12-23 12:54                         ` Eric Blake
2009-12-23 19:23                           ` OGAWA Hirofumi
     [not found]                           ` <4B32B303.6070807@gmail.com>
2009-12-24  0:50                             ` Eric Blake
2009-12-23 14:28                         ` Jean-Pierre André
2009-12-22 12:34           ` Dave Chinner
2009-12-22 12:42             ` Eric Blake
2009-12-23  7:53               ` Christoph Hellwig
2009-12-22 17:45         ` Christoph Hellwig
2009-12-22 19:06           ` OGAWA Hirofumi

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