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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AD20C3A5A2 for ; Fri, 23 Aug 2019 14:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0784D2173E for ; Fri, 23 Aug 2019 14:16:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392736AbfHWOQz (ORCPT ); Fri, 23 Aug 2019 10:16:55 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:40603 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388188AbfHWOQy (ORCPT ); Fri, 23 Aug 2019 10:16:54 -0400 Received: from callcc.thunk.org (guestnat-104-133-0-111.corp.google.com [104.133.0.111] (may be forged)) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x7NEGjPq023423 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 23 Aug 2019 10:16:46 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 0C42042049E; Fri, 23 Aug 2019 10:16:45 -0400 (EDT) Date: Fri, 23 Aug 2019 10:16:45 -0400 From: "Theodore Y. Ts'o" To: Ayush Ranjan Cc: Andreas Dilger , Jonathan Corbet , Ext4 Developers List , linux-doc@vger.kernel.org, Linux Kernel Mailing List Subject: Re: [PATCH v2] Ext4 documentation fixes. Message-ID: <20190823141644.GG8130@mit.edu> Mail-Followup-To: "Theodore Y. Ts'o" , Ayush Ranjan , Andreas Dilger , Jonathan Corbet , Ext4 Developers List , linux-doc@vger.kernel.org, Linux Kernel Mailing List References: <20190823031801.GD8130@mit.edu> <71dfe444-3efb-5f1c-d8a1-bb0e98002fd1@mixmax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <71dfe444-3efb-5f1c-d8a1-bb0e98002fd1@mixmax.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 23, 2019 at 04:56:42AM +0000, Ayush Ranjan wrote: > Hey Ted! > Thanks for reviewing! The comment in fs/ext4/ext4.h:ext4_group_desc:bg_checksum > says that the crc16 checksum formula should be crc16(sb_uuid+group+desc). I > think group over here denotes group number. > > Briefly looking through fs/ext4/super.c:ext4_group_desc_csum() suggests that: > - For the new metadata_csum algorithm, only the group number and the block > descriptor are included in the checksum. So the formula should be > crc32c(group+desc) & 0xFFF (this looks like a bug as this should also include sb > UUID?) > - For the old crc16 algorithm, the sb UUID, group number and the block > descriptor are included in the checksum. So the formula should be > crc16(sb\_uuid+group+desc). (should remain unchanged) Thanks for the research and explanation. I think I'm going to change that to be: crc{16,32c}(sb_uuid + group_num + bg_desc) That should make it clearer what is meant. - Ted > > Ayush Ranjan > University of Illinois - Urbana Champaign | May 2020 > Bachelors of Science in Computer Science and Mathematics > Business Minor | Gies College of Business > > > On Fri, Aug 23, 2019 at 8:48 AM Theodore Y. Ts'o wrote: > > > > On Thu, Aug 15, 2019 at 09:11:51AM -0700, Ayush Ranjan wrote: > > > This commit aims to fix the following issues in ext4 documentation: > > > - Flexible block group docs said that the aim was to group block > > >   metadata together instead of block group metadata. > > > - The documentation consistly uses "location" instead of "block number". > > >   It is easy to confuse location to be an absolute offset on disk. Added > > >   a line to clarify all location values are in terms of block numbers. > > > - Dirent2 docs said that the rec_len field is shortened instead of the > > >   name_len field. > > > - Typo in bg_checksum description. > > > - Inode size is 160 bytes now, and hence i_extra_isize is now 32. > > > - Cluster size formula was incorrect, it did not include the +10 to > > >   s_log_cluster_size value. > > > - Typo: there were two s_wtime_hi in the superblock struct. > > > - Superblock struct was outdated, added the new fields which were part > > >   of s_reserved earlier. > > > - Multiple mount protection seems to be implemented in fs/ext4/mmp.c. > > > > > > Signed-off-by: Ayush Ranjan > > > > Fixed with one minor typo fix: > > > > > diff --git a/Documentation/filesystems/ext4/group_descr.rst > > > b/Documentation/filesystems/ext4/group_descr.rst > > > index 0f783ed88..feb5c613d 100644 > > > --- a/Documentation/filesystems/ext4/group_descr.rst > > > +++ b/Documentation/filesystems/ext4/group_descr.rst > > > @@ -100,7 +100,7 @@ The block group descriptor is laid out in ``struct > > > ext4_group_desc``. > > >       - \_\_le16 > > >       - bg\_checksum > > >       - Group descriptor checksum; crc16(sb\_uuid+group+desc) if the > > > -       RO\_COMPAT\_GDT\_CSUM feature is set, or > crc32c(sb\_uuid+group\_desc) & > > > +       RO\_COMPAT\_GDT\_CSUM feature is set, or crc32c(sb\_uuid+group+desc) > & > > >         0xFFFF if the RO\_COMPAT\_METADATA\_CSUM feature is set. > > > > The correct checksum should be "crc16(sb\_uuid+group\_desc)" or > > "crc32c(sb\_uuid+group\_desc)".  That is, it's previous line which > > needed modification. > > > >                                         - Ted