From patchwork Fri Aug 26 21:46:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Layton X-Patchwork-Id: 12956629 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 30610C0502A for ; Fri, 26 Aug 2022 21:47:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345120AbiHZVrQ (ORCPT ); Fri, 26 Aug 2022 17:47:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238322AbiHZVrL (ORCPT ); Fri, 26 Aug 2022 17:47:11 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4917FBE4CB; Fri, 26 Aug 2022 14:47:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D8D1F61263; Fri, 26 Aug 2022 21:47:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5204FC433C1; Fri, 26 Aug 2022 21:47:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661550429; bh=D45PYjSz97etPghw1Xih5xud6PKdbXoB4GAMHrVTVWY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PfAdfILJwEYpDoeED324CpLATv+DqXE7iT1H9OOHA29yxVF5zVdLnEY2bAXyse7F7 mCWxe/uHySvmYJqWnINspAB9GBdK9PNqasigc+of1xQQ0LWgpnkuzTpfRuJ6eWX3mb gymePYkysSn3UXTQmxBUamknsmDWTMm2xVHuvQTMwMJYAJqJXCp+uO3UO+bZbWpHAl kRH+h1xnEZ6a+PGkWltbtzGqkAeLibIu89QbBb3T9HjAZ5mry+eVDpwtJngKKDAgqh u5f7SCkCH2ulASydhyZvIPrUG1HH/qMAzHkpqRNmOKUJJjv8NAeX/GKdDQE/rZMois uFX0CayIEkpKQ== From: Jeff Layton To: tytso@mit.edu, adilger.kernel@dilger.ca, djwong@kernel.org, david@fromorbit.com, trondmy@hammerspace.com, neilb@suse.de, viro@zeniv.linux.org.uk, zohar@linux.ibm.com, xiubli@redhat.com, chuck.lever@oracle.com, lczerner@redhat.com, jack@suse.cz, brauner@kernel.org Cc: linux-api@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ceph@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org, Colin Walters Subject: [PATCH v3 1/7] iversion: update comments with info about atime updates Date: Fri, 26 Aug 2022 17:46:57 -0400 Message-Id: <20220826214703.134870-2-jlayton@kernel.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220826214703.134870-1-jlayton@kernel.org> References: <20220826214703.134870-1-jlayton@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org The i_version field in the kernel has had different semantics over the decades, but we're now proposing to expose it to userland via statx. This means that we need a clear, consistent definition of what it means and when it should change. Update the comments in iversion.h to describe how a conformant i_version implementation is expected to behave. This definition suits the current users of i_version (NFSv4 and IMA), but is loose enough to allow for a wide range of possible implementations. Cc: Colin Walters Cc: NeilBrown Cc: Trond Myklebust Cc: Dave Chinner Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t Signed-off-by: Jeff Layton --- include/linux/iversion.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/include/linux/iversion.h b/include/linux/iversion.h index 3bfebde5a1a6..45e93e1b4edc 100644 --- a/include/linux/iversion.h +++ b/include/linux/iversion.h @@ -9,8 +9,19 @@ * --------------------------- * 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. + * + * An explicit change is one that would ordinarily result in a change to the + * inode status change time (aka ctime). The version must appear to change, even + * if the ctime does not (since the whole point is to avoid missing updates due + * to timestamp granularity). If POSIX mandates that the ctime must change due + * to an operation, then the i_version counter must be incremented as well. + * + * A conformant implementation is allowed to increment the counter in other + * cases, but this is not optimal. NFSv4 and IMA both use this value to determine + * whether caches are up to date. Spurious increments can cause false cache + * invalidations. * * 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 @@ -66,6 +77,14 @@ * Storing the value to disk therefore does not count as a query, so those * filesystems should use inode_peek_iversion to grab the value to be stored. * There is no need to flag the value as having been queried in that case. + * + * Notes on atime updates + * ---------------------- + * Access time (atime) updates due to reads or similar activity do not represent + * an explicit change to the inode data or metadata. If the only change to the + * inode is the atime, then i_version should not be incremented. If an observer + * cares about atime updates, it should plan to fetch and store the atime in + * conjunction with the i_version. */ /*