linux-kernel - Re: [PATCH] iversion: update comments with info about atime updates

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Message-ID: <ceb8f09a4cb2de67f40604d03ee0c475feb3130a.camel@linux.ibm.com>
Date:   Mon, 22 Aug 2022 11:40:39 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Jeff Layton <jlayton@...nel.org>, linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, NeilBrown <neilb@...e.de>,
        Trond Myklebust <trondmy@...merspace.com>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH] iversion: update comments with info about atime updates

On Mon, 2022-08-22 at 09:33 -0400, Jeff Layton wrote:
> Add an explicit paragraph codifying that atime updates due to reads
> should not be counted against the i_version counter. None of the
> existing subsystems that use the i_version want those counted, and
> there is an easy workaround for those that do.
> 
> Cc: NeilBrown <neilb@...e.de>
> Cc: Trond Myklebust <trondmy@...merspace.com>
> Cc: Dave Chinner <david@...morbit.com>
> Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  include/linux/iversion.h | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> index 3bfebde5a1a6..da6cc1cc520a 100644
> --- a/include/linux/iversion.h
> +++ b/include/linux/iversion.h
> @@ -9,8 +9,8 @@
>   * ---------------------------
>   * The change attribute (i_version) is mandated by NFSv4 and is mostly for
>   * knfsd, but is also used for other purposes (e.g. IMA). The i_version must
> - * appear different to observers if there was a change to the inode's data or
> - * metadata since it was last queried.
> + * appear different to observers if there was an explicit change to the inode's
> + * data or metadata since it was last queried.
>   *
>   * Observers see the i_version as a 64-bit number that never decreases. If it
>   * remains the same since it was last checked, then nothing has changed in the
> @@ -18,6 +18,12 @@
>   * anything about the nature or magnitude of the changes from the value, only
>   * that the inode has changed in some fashion.
>   *
> + * Note that atime updates due to reads or similar activity do _not_ represent
> + * an explicit change to the inode. If the only change is to the atime and it

Thanks, Jeff.  The ext4 patch increments i_version on file metadata
changes.  Could the wording here be more explicit to reflect changes
based on either inode data or metadata changes?

thanks,

Mimi

> + * wasn't set via utimes() or a similar mechanism, then i_version should not be
> + * incremented. If an observer cares about atime updates, it should plan to
> + * fetch and store them in conjunction with the i_version.
> + *
>   * Not all filesystems properly implement the i_version counter. Subsystems that
>   * want to use i_version field on an inode should first check whether the
>   * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro).