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 331FEECAAD5 for ; Fri, 9 Sep 2022 15:45:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231824AbiIIPpO (ORCPT ); Fri, 9 Sep 2022 11:45:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230108AbiIIPpJ (ORCPT ); Fri, 9 Sep 2022 11:45:09 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 048067391B; Fri, 9 Sep 2022 08:45:07 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id 090513EFA; Fri, 9 Sep 2022 11:45:07 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 090513EFA DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1662738307; bh=V/DLdRPq1zvs/q2asuE3/COTboZaddvEjKL48nZq+Ag=; h=Date:To:Cc:Subject:References:In-Reply-To:From:From; b=nst+nwaO6YbS4rXF/b6lFwOretBhbDsuXZPoezitk+nlqiztyBadpNSM4FUr7jnwg 8MJVasi6mMG6bgkD27Rw1rr7K/yhOcWkv0PLxFUO25Jk7I2jBCLUizMlSPpqpB05Pm j19t4ySKDY3IIRE1n2ES5Fq9mNY9GKx9BLcF0ZUY= Date: Fri, 9 Sep 2022 11:45:06 -0400 To: Jeff Layton Cc: Theodore Ts'o , Jan Kara , NeilBrown , 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 Message-ID: <20220909154506.GB5674@fieldses.org> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44efe219dbf511492b21a653905448d43d0f3363.camel@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) From: bfields@fieldses.org (J. Bruce Fields) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 08, 2022 at 03:07:58PM -0400, 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. > > 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? I was assuming we could partition i_version's 64 bits somehow: e.g., top 16 bits store the crash counter. You increment the i_version by: 1) replacing the top bits by the new crash counter, if it has changed, and 2) incrementing. Do the numbers work out? 2^16 mounts after unclean shutdowns sounds like a lot for one filesystem, as does 2^48 changes to a single file, but people do weird things. Maybe there's a better partitioning, or some more flexible way of maintaining an i_version that still allows you to identify whether a given i_version preceded a crash. --b.