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 B849AC001DE for ; Tue, 1 Aug 2023 02:47:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230064AbjHACrw (ORCPT ); Mon, 31 Jul 2023 22:47:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40780 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229510AbjHACru (ORCPT ); Mon, 31 Jul 2023 22:47:50 -0400 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4AE24114 for ; Mon, 31 Jul 2023 19:47:49 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046049;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0Vojef4e_1690858064; Received: from 30.221.145.62(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0Vojef4e_1690858064) by smtp.aliyun-inc.com; Tue, 01 Aug 2023 10:47:46 +0800 Message-ID: <2d554e41-16d8-706d-20ae-4b03894384c0@linux.alibaba.com> Date: Tue, 1 Aug 2023 10:47:40 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v2] erofs: deprecate superblock checksum feature Content-Language: en-US To: =?UTF-8?Q?Thomas_Wei=c3=9fschuh?= , Gao Xiang Cc: chao@kernel.org, huyue2@coolpad.com, linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, Karel Zak References: <20230717112703.60130-1-jefflexu@linux.alibaba.com> <9299dd4c-c2da-4ed1-8979-87fa44c68f77@t-8ch.de> From: Jingbo Xu In-Reply-To: <9299dd4c-c2da-4ed1-8979-87fa44c68f77@t-8ch.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Thomas, On 7/30/23 10:28 PM, Thomas Weißschuh wrote: > Hi Gao! > > On 2023-07-30 22:01:11+0800, Gao Xiang wrote: >> On 2023/7/30 21:31, Thomas Weißschuh wrote: >>> On 2023-07-17 19:27:03+0800, Jingbo Xu wrote: >>>> Later we're going to try the self-contained image verification. >>>> The current superblock checksum feature has quite limited >>>> functionality, instead, merkle trees can provide better protection >>>> for image integrity. >>> >>> The crc32c checksum is also used by libblkid to gain more confidence >>> in its filesystem detection. >>> I guess a merkle tree would be much harder to implement. >>> >>> This is for example used by the mount(8) cli program to allow mounting >>> of devices without explicitly needing to specify a filesystem. >>> >>> Note: libblkid tests for EROFS_FEATURE_SB_CSUM so at least it won't >>> break when the checksum is removed. > >> I'm not sure if we could switch EROFS_FEATURE_SB_CSUM to a simpler >> checksum instead (e.g. just sum each byte up if both >> EROFS_FEATURE_SB_CSUM and COMPAT_XATTR_FILTER bits are set, or >> ignore checksums completely at least in the kernel) if the better >> filesystem detection by using sb chksum is needed (not sure if other >> filesystems have sb chksum or just do magic comparsion)? > > Overloading EROFS_FEATURE_SB_CSUM in combination with > COMPAT_XATTR_FILTER would break all existing deployments of libblkid, so > it's not an option. > > All other serious and halfway modern filesystems do have superblock > checksums which are also checked by libblkid. > >> The main problem here is after xattr name filter feature is added >> (xxhash is generally faster than crc32c), there could be two >> hard-depended hashing algorithms, this increases more dependency >> especially for embededed devices. > > From libblkid side nothing really speaks against a simpler checksum. > XOR is easy to implement and xxhash is already part of libblkid for > other filesystems. > > The drawbacks are: > * It would need a completely new feature bit in erofs. > * Old versions of libblkid could not validate checksums on newer > filesystems. Thanks for pointing this out. we indeed need further discussion for a better solution. As mentioned previously, we don't want two hashing algorithms dependency for erofs. The best idea as far as I can come up with is that, introduce a new feature bit indicating XOR hashing algorithm for the sb checksum, while the original EROFS_FEATURE_SB_CSUM is not set. As for the old version libblkid, only fs magic is available for the fs type detection, not perfect but in a best-effort way. -- Thanks, Jingbo