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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 815A7C001DE for ; Sun, 30 Jul 2023 14:37:32 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4RDP965v7Cz2yG9 for ; Mon, 31 Jul 2023 00:37:30 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.99; helo=out30-99.freemail.mail.aliyun.com; envelope-from=hsiangkao@linux.alibaba.com; receiver=lists.ozlabs.org) Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4RDP926x8lz2yDT for ; Mon, 31 Jul 2023 00:37:25 +1000 (AEST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=hsiangkao@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VoW-1km_1690727840; Received: from 192.168.75.41(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0VoW-1km_1690727840) by smtp.aliyun-inc.com; Sun, 30 Jul 2023 22:37:21 +0800 Message-ID: Date: Sun, 30 Jul 2023 22:37:19 +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 To: =?UTF-8?Q?Thomas_Wei=c3=9fschuh?= References: <20230717112703.60130-1-jefflexu@linux.alibaba.com> <9299dd4c-c2da-4ed1-8979-87fa44c68f77@t-8ch.de> From: Gao Xiang In-Reply-To: <9299dd4c-c2da-4ed1-8979-87fa44c68f77@t-8ch.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: huyue2@coolpad.com, linux-kernel@vger.kernel.org, Karel Zak , linux-erofs@lists.ozlabs.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" On 2023/7/30 22:28, 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. I think for libblkid, you could still use: EROFS_FEATURE_SB_CSUM is not set, don't check anything; EROFS_FEATURE_SB_CSUM only is set, check with crc32c; EROFS_FEATURE_SB_CSUM | COMPAT_XATTR_FILTER (or some other bit) is set, check with a simpler hash? > > 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. just checking magic for Old versions of libblkid will cause false positive in which extent? Thanks, Gao Xiang