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 5A2E1C6FA82 for ; Thu, 8 Sep 2022 23:01:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229807AbiIHXBd (ORCPT ); Thu, 8 Sep 2022 19:01:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229747AbiIHXBb (ORCPT ); Thu, 8 Sep 2022 19:01:31 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5CC4B82D07; Thu, 8 Sep 2022 16:01:30 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id D0A3D336AE; Thu, 8 Sep 2022 23:01:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1662678087; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xy/c6DrfacbSWG6gKyZHom3flbC+WLVPqFWDGXwmFQw=; b=IeUqcmcN2pH1qmadf0Pchq9/88nnlj0PxSIlEX2iIxcVgzyqofXNRW4tFrA7RcpXSot6xS 0k5Zq69AnsyFOMA+k+sUEkRzgWv0k7z6NNtsubduewv57ktYqrzRWk4HPHfF5AIwX0o9dc vdHAgxJ6HhoUyoufPpa7bKSIf+2J8fw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1662678087; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xy/c6DrfacbSWG6gKyZHom3flbC+WLVPqFWDGXwmFQw=; b=ygJFcjmFtUS7tcIiTptD8Wumi8jQDvwi/mc1uB+J7WNwXp5qeZcsDUxFASW0jiKo/3xInC IourZPWz6WE6vJAA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 4AD2B13A6D; Thu, 8 Sep 2022 23:01:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id wQFoAEB0GmNwEQAAMHmgww (envelope-from ); Thu, 08 Sep 2022 23:01:20 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit MIME-Version: 1.0 From: "NeilBrown" To: "Jeff Layton" 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 Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field In-reply-to: <44efe219dbf511492b21a653905448d43d0f3363.camel@kernel.org> 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> Date: Fri, 09 Sep 2022 09:01:16 +1000 Message-id: <166267807678.30452.18035749642786839300@noble.neil.brown.name> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org 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, we'd > > > mix that in when we store the i_version rather than adding it afterward. > > > > > > Ted, how would we access this? Maybe we could just add a new (generic) > > > super_block field for this that ext4 (and other filesystems) could > > > populate at mount time? > > > > Couldn't the filesystem just return an ino_version that already includes > > it? > > > > 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 less > clear on how that will work. > > Maybe I need a concrete example of how that will work: > > 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. 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. 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. "add" and "subtract" could be any reversible hash, and its inverse. I would probably shift the crash counter up 16 and add/subtract. NeilBrown > > 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? > -- > Jeff Layton >