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Subject: Re: [PATCH v7 05/13] fat: make fat_update_time get its own timestamp
From:   Jeff Layton <jlayton@kernel.org>
To:     OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        Frank Sorenson <sorenson@redhat.com>
Cc:     Jan Kara <jack@suse.cz>, Alexander Viro <viro@zeniv.linux.org.uk>,
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Date:   Wed, 09 Aug 2023 18:07:29 -0400
In-Reply-To: <87a5v06kij.fsf@mail.parknet.co.jp>
References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org>
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         <87msz08vc7.fsf@mail.parknet.co.jp>
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         <878rak8hia.fsf@mail.parknet.co.jp>
         <20230809150041.452w7gucjmvjnvbg@quack3>
         <87v8do6y8q.fsf@mail.parknet.co.jp>
         <2cb998ff14ace352a9dd553e82cfa0aa92ec09ce.camel@kernel.org>
         <87leek6rh1.fsf@mail.parknet.co.jp>
         <ccffe6ca3397c8374352b002fe01d55b09d84ef4.camel@kernel.org>
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On Thu, 2023-08-10 at 05:14 +0900, OGAWA Hirofumi wrote:
> Jeff Layton <jlayton@kernel.org> writes:
>=20
> > When you say it "doesn't work the same", what do you mean, specifically=
?
> > I had to make some allowances for the fact that FAT is substantially
> > different in its timestamp handling, and I tried to preserve existing
> > behavior as best I could.
>=20
> Ah, ok. I was misreading some.
>=20
> inode_update_timestamps() checks IS_I_VERSION() now, not S_VERSION.  So,
> if adding the check of IS_I_VERSION() and (S_MTIME|S_CTIME|S_VERSION) to
> FAT?
>=20
> With it, IS_I_VERSION() would be false on FAT, and I'm fine.
>=20
> I.e. something like
>=20
> 	if ((flags & (S_VERSION|S_CTIME|S_MTIME)) && IS_I_VERSION(inode)
> 	    && inode_maybe_inc_iversion(inode, false))
>   		dirty_flags |=3D I_DIRTY_SYNC;
>=20
> Thanks.

If you do that then the i_version counter would never be incremented.
But...I think I see what you're getting at.

Most filesystems that support the i_version counter have an on-disk
field for it. FAT obviously has no such thing. I suspect the i_version
bits in fat_update_time were added by mistake. FAT doesn't set
SB_I_VERSION so there's no need to do anything to the i_version field at
all.

Also, given that the mtime and ctime are always kept in sync on FAT,
we're probably fine to have it look something like this:

--------------------8<------------------
int fat_update_time(struct inode *inode, int flags)=20
{=20
        int dirty_flags =3D 0;

        if (inode->i_ino =3D=3D MSDOS_ROOT_INO)=20
                return 0;

        fat_truncate_time(inode, NULL, flags);
        if (inode->i_sb->s_flags & SB_LAZYTIME)
                dirty_flags |=3D I_DIRTY_TIME;
        else
                dirty_flags |=3D I_DIRTY_SYNC;

        __mark_inode_dirty(inode, dirty_flags);
        return 0;
}=20
--------------------8<------------------

...and we should probably do that in a separate patch in advance of the
update_time rework, since it's really a different change.

If you're in agreement, then I'll plan to respin the series with this
fixed and resend.

Thanks for being patient!
--=20
Jeff Layton <jlayton@kernel.org>