Re: [RFC v2 03/83] Add super.h.

Darrick J. Wong
2018-03-16T06:37:12Z

On Thu, Mar 15, 2018 at 11:17:54PM -0700, Andiry Xu wrote:
> On Thu, Mar 15, 2018 at 7:59 PM, Theodore Y. Ts'o <tytso@mit.edu> wrote:
> > On Thu, Mar 15, 2018 at 09:38:29PM +0100, Arnd Bergmann wrote:
> >>
> >> You could also have a resolution of less than a nanosecond. Note
> >> that today, the file time stamps generated by the kernel are in
> >> jiffies resolution, so at best one millisecond. However, most modern
> >> file systems go with the 64+32 bit timestamps because it's not all
> >> that expensive.
> >
> > It actually depends on the architecture and the accuracy/granularity
> > of the timekeeping hardware available to the system, but it's possible
> > for the granularity of file time stamps to be up to one nanosecond.
> > So you can get results like this:
> >
> > % stat unix_io.o
> > File: unix_io.o
> > Size: 55000 Blocks: 112 IO Block: 4096 regular file
> > Device: fc01h/64513d Inode: 19931278 Links: 1
> > Access: (0644/-rw-r--r--) Uid: (15806/ tytso) Gid: (15806/ tytso)
> > Access: 2018-03-15 18:09:21.679914182 -0400
> > Modify: 2018-03-15 18:09:21.639914089 -0400
> > Change: 2018-03-15 18:09:21.639914089 -0400
> >
>
> Thanks for all the suggestions. I think I will follow ext4's time
> format. 2446 should be far away enough.

If you do, try to avoid the encoding problems that ext4 (still) has:

Not-fixed-by: a4dad1ae24f8 ("ext4: Fix handling of extended tv_sec")

--D

> Thanks,
> Andiry