linux-ext4 - Re: [PATCH v7 05/13] fat: make fat_update

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Date:   Wed, 09 Aug 2023 18:07:29 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Frank Sorenson <sorenson@...hat.com>
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Subject: Re: [PATCH v7 05/13] fat: make fat_update_time get its own timestamp

On Thu, 2023-08-10 at 05:14 +0900, OGAWA Hirofumi wrote:
> Jeff Layton <jlayton@...nel.org> writes:
> 
> > 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.
> 
> Ah, ok. I was misreading some.
> 
> 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?
> 
> With it, IS_I_VERSION() would be false on FAT, and I'm fine.
> 
> I.e. something like
> 
> 	if ((flags & (S_VERSION|S_CTIME|S_MTIME)) && IS_I_VERSION(inode)
> 	    && inode_maybe_inc_iversion(inode, false))
>   		dirty_flags |= I_DIRTY_SYNC;
> 
> 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) 
{ 
        int dirty_flags = 0;

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

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

        __mark_inode_dirty(inode, dirty_flags);
        return 0;
} 
--------------------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!
-- 
Jeff Layton <jlayton@...nel.org>