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/* Assist in file system timestamp tests.
Copyright (C) 2009-2013 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Written by Eric Blake <ebb9@byu.net>, 2009. */
#ifndef GLTEST_NAP_H
# define GLTEST_NAP_H
static int
lt_mtime (struct stat const *a, struct stat const *b)
{
time_t as = a->st_mtime;
time_t bs = b->st_mtime;
int ans = get_stat_mtime_ns (a);
int bns = get_stat_mtime_ns (b);
return as < bs || (as == bs && ans < bns);
}
static void
get_mtime (int fd, struct stat *st, int do_write)
{
if (do_write)
ASSERT (write (fd, "\n", 1) == 1);
ASSERT (fstat (fd, st) == 0);
}
/* Given a file whose descriptor is FD, see whether delaying by DELAY
microseconds causes a change in a file's time stamp. If the time
stamps differ, repeat the test one more time, in case we crossed a
quantization boundary on a file system with lower resolution. *ST
is the file's status, recently gotten. Update *ST to reflect the
latest status gotten. */
static int
nap_works (int fd, int delay, struct stat *st)
{
struct stat old_st;
old_st = *st;
usleep (delay);
get_mtime (fd, st, 1);
if (! lt_mtime (&old_st, st))
return 0;
old_st = *st;
usleep (delay);
get_mtime (fd, st, 1);
return lt_mtime (&old_st, st);
}
static int
guess_delay (void)
{
/* Try a 1-microsecond sleep first, for speed. If that doesn't
work, try a 1 ms sleep; that should work with ext. If it doesn't
work, try a 20 ms sleep. xfs has a quantization of about 10
milliseconds, even though it has a granularity of 1 nanosecond,
and NTFS has a default quantization of 15.25 milliseconds, even
though it has a granularity of 100 nanoseconds, so 20 ms is a
good quantization to try. If that doesn't work, try 1 second.
The worst case is 2 seconds, needed for FAT. */
static int const delaytab[] = {1, 1000, 20000, 1000000 };
int fd = creat (BASE "tmp", 0600);
int i;
int delay = 2000000;
struct stat st;
ASSERT (0 <= fd);
get_mtime (fd, &st, 0);
for (i = 0; i < sizeof delaytab / sizeof delaytab[0]; i++)
if (nap_works (fd, delaytab[i], &st))
{
delay = delaytab[i];
break;
}
ASSERT (close (fd) == 0);
ASSERT (unlink (BASE "tmp") == 0);
return delay;
}
/* Sleep long enough to notice a timestamp difference on the file
system in the current directory. Assumes that BASE is defined,
and requires that the test module depends on usleep. */
static void
nap (void)
{
static int delay;
if (!delay)
delay = guess_delay ();
usleep (delay);
}
#endif /* GLTEST_NAP_H */
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