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From:   OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To:     Jeff Layton <jlayton@kernel.org>
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Subject: Re: [PATCH v7 05/13] fat: make fat_update_time get its own timestamp
In-Reply-To: <7edc9239f73022b9c2a1d3f4f946153f85f94739.camel@kernel.org> (Jeff
        Layton's message of "Wed, 09 Aug 2023 10:22:54 -0400")
References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org>
        <20230807-mgctime-v7-5-d1dec143a704@kernel.org>
        <87msz08vc7.fsf@mail.parknet.co.jp>
        <52bead1d6a33fec89944b96e2ec20d1ea8747a9a.camel@kernel.org>
        <878rak8hia.fsf@mail.parknet.co.jp>
        <7edc9239f73022b9c2a1d3f4f946153f85f94739.camel@kernel.org>
Date:   Wed, 09 Aug 2023 23:44:26 +0900
Message-ID: <874jl88ed1.fsf@mail.parknet.co.jp>
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Jeff Layton <jlayton@kernel.org> writes:

> I'm a little confused too. Why do you believe this will break
> -o relatime handling? This patch changes two things:
>
> 1/ it has fat_update_time fetch its own timestamp (and ignore the "now"
> parameter). This is in line with the changes in patch #3 of this series,
> which explains the rationale for this in more detail.
>
> 2/ it changes fat_update_time to also update the i_version if any of
> S_CTIME|S_MTIME|S_VERSION are set. relatime is all about the S_ATIME,
> and it is specifically excluded from that set.
>
> The rationale for the second change is is also in patch #3, but
> basically, we can't guarantee that current_time hasn't changed since we
> last checked for inode_needs_update_time, so if any of
> S_CTIME/S_MTIME/S_VERSION have changed, then we need to assume that any
> of them may need to be changed and attempt to update all 3.
>
> That said, I think the logic in fat_update_time isn't quite right. I
> think want something like this on top of this patch to ensure that the
> S_CTIME and S_MTIME get updated, even if the flags only have S_VERSION
> set.
>
> Thoughts?

I'm not talking about "relatime" at all, I'm always talking about
"lazytime".

I_DIRTY_TIME delays to update on disk inode only if changed
timestamp. But you changed it to I_DIRTY_SYNC, i.e. always update on
disk inode by timestamp.

Thanks.

> ---------------------8<-----------------------
>
> diff --git a/fs/fat/misc.c b/fs/fat/misc.c
> index 080a5035483f..313eef02f45c 100644
> --- a/fs/fat/misc.c
> +++ b/fs/fat/misc.c
> @@ -346,15 +346,21 @@ int fat_update_time(struct inode *inode, int flags)
>         if (inode->i_ino == MSDOS_ROOT_INO)
>                 return 0;
>  
> -       if (flags & (S_ATIME | S_CTIME | S_MTIME)) {
> -               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;
> -       }
> +       /*
> +        * If any of the flags indicate an expicit change to the file, then we
> +        * need to ensure that we attempt to update all of 3. We do not do
> +        * this in the case of an S_ATIME-only update.
> +        */
> +       if (flags & (S_CTIME | S_MTIME | S_VERSION))
> +               flags |= S_CTIME | S_MTIME | S_VERSION;
> +
> +       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;
>  
> -       if ((flags & (S_VERSION|S_CTIME|S_MTIME)) && inode_maybe_inc_iversion(inode, false))
> +       if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
>                 dirty_flags |= I_DIRTY_SYNC;
>

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>