On Tue 19-09-23 15:05:24, Xi Ruoyao wrote: > On Mon, 2023-08-07 at 15:38 -0400, Jeff Layton wrote: > > Enable multigrain timestamps, which should ensure that there is an > > apparent change to the timestamp whenever it has been written after > > being actively observed via getattr. > > > > For ext4, we only need to enable the FS_MGTIME flag. > > Hi Jeff, > > This patch causes a gnulib test failure: > > $ ~/sources/lfs/grep-3.11/gnulib-tests/test-stat-time > test-stat-time.c:141: assertion 'statinfo[0].st_mtime < statinfo[2].st_mtime || (statinfo[0].st_mtime == statinfo[2].st_mtime && (get_stat_mtime_ns (&statinfo[0]) < get_stat_mtime_ns (&statinfo[2])))' failed > Aborted (core dumped) > > The source code of the test: > https://git.savannah.gnu.org/cgit/gnulib.git/tree/tests/test-stat-time.c > > Is this an expected change? Kind of yes. The test first tries to estimate filesystem timestamp granularity in nap() function - due to this patch, the detected granularity will likely be 1 ns so effectively all the test calls will happen immediately one after another. But we don't bother setting the timestamps with more than 1 jiffy (usually 4 ms) precision unless we think someone is watching. So as a result timestamps of all stamp1 and stamp2 files are going to be equal which makes the test fail. The ultimate problem is that a sequence like: write(f1) stat(f2) write(f2) stat(f2) write(f1) stat(f1) can result in f1 timestamp to be (slightly) lower than the final f2 timestamp because the second write to f1 didn't bother updating the timestamp. That can indeed be a bit confusing to programs if they compare timestamps between two files. Jeff? Honza > > Acked-by: Theodore Ts'o <tytso@xxxxxxx> > > Reviewed-by: Jan Kara <jack@xxxxxxx> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > --- > > fs/ext4/super.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > > index b54c70e1a74e..cb1ff47af156 100644 > > --- a/fs/ext4/super.c > > +++ b/fs/ext4/super.c > > @@ -7279,7 +7279,7 @@ static struct file_system_type ext4_fs_type = { > > .init_fs_context = ext4_init_fs_context, > > .parameters = ext4_param_specs, > > .kill_sb = kill_block_super, > > - .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP, > > + .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | > > FS_MGTIME, > > }; > > MODULE_ALIAS_FS("ext4"); > > > > > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
