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

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Date:   Thu, 15 Mar 2018 23:30:45 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Andiry Xu <jix024@....ucsd.edu>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "Rudoff, Andy" <andy.rudoff@...el.com>, coughlan@...hat.com,
        Steven Swanson <swanson@...ucsd.edu>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        swhiteho@...hat.com, miklos@...redi.hu,
        Jian Xu <andiry.xu@...il.com>, Andiry Xu <jix024@...ucsd.edu>
Subject: Re: [RFC v2 03/83] Add super.h.

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@....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