From mboxrd@z Thu Jan 1 00:00:00 1970 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 9F55DC6FA83 for ; Thu, 8 Sep 2022 23:23:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229945AbiIHXXo (ORCPT ); Thu, 8 Sep 2022 19:23:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229549AbiIHXXn (ORCPT ); Thu, 8 Sep 2022 19:23:43 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3F2162705; Thu, 8 Sep 2022 16:23:42 -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 ams.source.kernel.org (Postfix) with ESMTPS id E0FB6B822CC; Thu, 8 Sep 2022 23:23:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75E9CC433C1; Thu, 8 Sep 2022 23:23:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662679419; bh=nH3goiwh4MPlbyp6wbqIpdi/uAY7tWd6MeTco+vFrpI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=qRRZyY6jlpIBg7m7TJ+5c6bka15n1MoQlKCiCheWqANfJzVNRATy3aPNi5bXsWKqN +Im0EssEQvJ/xsPYz4KaAU27m+04C/mmI3E0oAJeJ5xDgJO9rDhkNXDK9BTy6jjwRw ASsPSLfUblxcT1iuhRHIWuexZf5KT25U2TCTokpMpyAFdqheZynGUVrIkq0LpDBtlK ACuy9x3fzecAnR7gQuMs5dLVeT8pek1/qrgTzkjT60UjMEO/BcpeB8lSrj8XdW31zi Guf0FVbBLdJh//f1ge+9feD618r1fVso65EwnjgOQbL3UQV+mdqyOjabi2fhqrgHOT Rdlozw8pCusJw== Message-ID: <53298467f5fce443c70ef6821e055d10caf9331e.camel@kernel.org> Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field From: Jeff Layton To: NeilBrown Cc: "J. Bruce Fields" , Theodore Ts'o , Jan Kara , adilger.kernel@dilger.ca, djwong@kernel.org, david@fromorbit.com, trondmy@hammerspace.com, viro@zeniv.linux.org.uk, zohar@linux.ibm.com, xiubli@redhat.com, chuck.lever@oracle.com, lczerner@redhat.com, brauner@kernel.org, fweimer@redhat.com, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org Date: Thu, 08 Sep 2022 19:23:36 -0400 In-Reply-To: <166267807678.30452.18035749642786839300@noble.neil.brown.name> References: <79aaf122743a295ddab9525d9847ac767a3942aa.camel@kernel.org> , <20220907125211.GB17729@fieldses.org> , <771650a814ab1ff4dc5473d679936b747d9b6cf5.camel@kernel.org> , <20220907135153.qvgibskeuz427abw@quack3> , <166259786233.30452.5417306132987966849@noble.neil.brown.name> , <20220908083326.3xsanzk7hy3ff4qs@quack3>, , <02928a8c5718590bea5739b13d6b6ebe66cac577.camel@kernel.org> , <20220908155605.GD8951@fieldses.org> , <9e06c506fd6b3e3118da0ec24276e85ea3ee45a1.camel@kernel.org> , <20220908182252.GA18939@fieldses.org> , <44efe219dbf511492b21a653905448d43d0f3363.camel@kernel.org> <166267807678.30452.18035749642786839300@noble.neil.brown.name> Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.44.4 (3.44.4-1.fc36) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, 2022-09-09 at 09:01 +1000, NeilBrown wrote: > On Fri, 09 Sep 2022, Jeff Layton wrote: > > On Thu, 2022-09-08 at 14:22 -0400, J. Bruce Fields wrote: > > > On Thu, Sep 08, 2022 at 01:40:11PM -0400, Jeff Layton wrote: > > > > Yeah, ok. That does make some sense. So we would mix this into the > > > > i_version instead of the ctime when it was available. Preferably, w= e'd > > > > mix that in when we store the i_version rather than adding it after= ward. > > > >=20 > > > > Ted, how would we access this? Maybe we could just add a new (gener= ic) > > > > super_block field for this that ext4 (and other filesystems) could > > > > populate at mount time? > > >=20 > > > Couldn't the filesystem just return an ino_version that already inclu= des > > > it? > > >=20 > >=20 > > Yes. That's simple if we want to just fold it in during getattr. If we > > want to fold that into the values stored on disk, then I'm a little les= s > > clear on how that will work. > >=20 > > Maybe I need a concrete example of how that will work: > >=20 > > Suppose we have an i_version value X with the previous crash counter > > already factored in that makes it to disk. We hand out a newer version > > X+1 to a client, but that value never makes it to disk. >=20 > As I understand it, the crash counter would NEVER appear in the on-disk > i_version. > The crash counter is stable while a filesystem is mounted so is the same > when loading an inode from disk and when writing it back. >=20 > When loading, add crash counter to on-disk i_version to provide > in-memory i_version. > when storing, subtract crash counter from in-memory i_version to provide > on-disk i_version. >=20 > "add" and "subtract" could be any reversible hash, and its inverse. I > would probably shift the crash counter up 16 and add/subtract. >=20 >=20 If you store the value with the crash counter already factored-in, then not every inode would end up being invalidated after a crash. If we try to mix it in later, the client will end up invalidating the cache even for inodes that had no changes. > >=20 > > The machine crashes and comes back up, and we get a query for i_version > > and it comes back as X. Fine, it's an old version. Now there is a write= . > > What do we do to ensure that the new value doesn't collide with X+1?= =20 > > --=20 > > Jeff Layton > >=20 --=20 Jeff Layton