bug#19607: issue with Emacs 24.4.1 but not with 24.3.1 : changed on disk; really edit the buffer

[Paul Eggert <eggert@cs.ucla.edu>]

[-- Attachment #1: Type: text/plain, Size: 701 bytes --]

I see from Jakob's email that the bug can be reproduced on CIFS without 
EncFS.  However, there's still something wrong here, as Emacs has code 
to work around the CIFS bug; see the comment about CIFS in 
emacs/src/fileio.c starting at line 4897, here:

http://git.savannah.gnu.org/cgit/emacs.git/tree/src/fileio.c?id=a56eab8259568ea1389e972623e46359e73c0233#n4897

Unfortunately, this workaround for the CIFS bug does not appear to 
suffice for EncFS over CIFS.

Bertrand, can you please try the attached program, both on plain CIFS 
and on EncFS over CIFS?  It attempts to mimic Emacs's actions more 
precisely than the previous test program, which may help us to narrow 
down the problem.  Thanks.

[-- Attachment #2: test.c --]
[-- Type: text/plain, Size: 1311 bytes --]

#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, st3;
  if (fstat (fd, &st1) != 0)
    return perror ("fstat"), 1;
  if (close (fd) != 0)
    return perror ("close"), 1;
  int fd2 = open(filename, O_WRONLY|O_CLOEXEC);
  if (fd2 < 0)
    return perror ("open 2"), 1;
  if (fstat (fd2, &st2) != 0)
    return perror ("fstat 2"), 1;
  if (close (fd2) != 0)
    return perror ("close 2"), 1;
  if (! (st1.st_mtim.tv_sec == st2.st_mtim.tv_sec
	 && st1.st_mtim.tv_nsec == st2.st_mtim.tv_nsec))
    printf ("Emacs should work around this POSIX-conformance bug.\n");
  sleep (2);
  if (stat (filename, &st3) != 0)
    return perror ("stat"), 1;
  if (! (st2.st_mtim.tv_sec == st3.st_mtim.tv_sec
	 && st2.st_mtim.tv_nsec == st3.st_mtim.tv_nsec))
    {
      printf ("Emacs does not work around this POSIX-conformance bug.\n");
      return 1;
    }
  return 0;
}