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From:   Deepa Dinamani <deepa.kernel@gmail.com>
Date:   Tue, 30 Jul 2019 17:08:30 -0700
Message-ID: <CABeXuvq_9YTTGZwmxO1WuEivuttDesNHKxeSQL5SsvkBSR884Q@mail.gmail.com>
Subject: Re: [PATCH 03/20] timestamp_truncate: Replace users of timespec64_trunc
To:     Anton Altaparmakov <anton@tuxera.com>
Cc:     OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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On Tue, Jul 30, 2019 at 3:28 PM Anton Altaparmakov <anton@tuxera.com> wrote=
:
>
> Hi Deepa,
>
> > On 30 Jul 2019, at 18:26, Deepa Dinamani <deepa.kernel@gmail.com> wrote=
:
> >
> > On Tue, Jul 30, 2019 at 1:27 AM OGAWA Hirofumi
> > <hirofumi@mail.parknet.co.jp> wrote:
> >>
> >> Deepa Dinamani <deepa.kernel@gmail.com> writes:
> >>
> >>> diff --git a/fs/fat/misc.c b/fs/fat/misc.c
> >>> index 1e08bd54c5fb..53bb7c6bf993 100644
> >>> --- a/fs/fat/misc.c
> >>> +++ b/fs/fat/misc.c
> >>> @@ -307,8 +307,9 @@ int fat_truncate_time(struct inode *inode, struct=
 timespec64 *now, int flags)
> >>>              inode->i_atime =3D (struct timespec64){ seconds, 0 };
> >>>      }
> >>>      if (flags & S_CTIME) {
> >>> -             if (sbi->options.isvfat)
> >>> -                     inode->i_ctime =3D timespec64_trunc(*now, 10000=
000);
> >>> +             if (sbi->options.isvfat) {
> >>> +                     inode->i_ctime =3D timestamp_truncate(*now, ino=
de);
> >>> +             }
> >>>              else
> >>>                      inode->i_ctime =3D fat_timespec64_trunc_2secs(*n=
ow);
> >>>      }
> >>
> >> Looks like broken. It changed to sb->s_time_gran from 10000000, and
> >> changed coding style.
> >
> > This is using a new api: timestamp_truncate(). granularity is gotten
> > by inode->sb->s_time_gran. See Patch [2/20]:
> > https://lkml.org/lkml/2019/7/29/1853
> >
> > So this is not broken if fat is filling in the right granularity in the=
 sb.
>
> It is broken for FAT because FAT has different granularities for differen=
t timestamps so it cannot put the correct value in the sb as that only allo=
ws one granularity.  Your patch is totally broken for fat as it would be im=
mediately obvious if you spent a few minutes looking at the code...

It seemed to me that FAT had already covered the special cases (2s and
1d) granularities by using internal functions. This one could also be
an inlined calculation, but I will just drop the FAT part from this
patch and leave it as is for now.

Thanks,
Deepa