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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 4E2AAC4361B for ; Fri, 18 Dec 2020 09:00:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0EB1A23A7D for ; Fri, 18 Dec 2020 09:00:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732884AbgLRI7l (ORCPT ); Fri, 18 Dec 2020 03:59:41 -0500 Received: from mx2.suse.de ([195.135.220.15]:55174 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732857AbgLRI7l (ORCPT ); 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200828132010.27886-1-nborisov@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 28.08.20 г. 16:20 ч., Nikolay Borisov wrote: > When a snapshot is created its root item is inserted in the root tree > with the 'offset' field set to the transaction id when the snapshot > was created. Immediately afterwards the offset is set to -1 so when > the same key is used to create DIR_ITEM/DIR_INDEX in the destination > file tree its offset is really set to -1. Root tree item: > > item 13 key (258 ROOT_ITEM 7) itemoff 12744 itemsize 439 > generation 7 root_dirid 256 bytenr 30703616 level 0 refs 1 > lastsnap 7 byte_limit 0 bytes_used 16384 flags 0x0(none) > uuid f13abf0d-b1f5-f34b-a179-fd1c2f89e762 > parent_uuid 51a74677-a077-4c21-bd87-2141a147ff85 > ctransid 7 otransid 7 stransid 0 rtransid 0 > ctime 1598441149.466822752 (2020-08-26 11:25:49) > otime 1598441149.467474846 (2020-08-26 11:25:49) > drop key (0 UNKNOWN.0 0) level 0 > > DIR_INDEX item for the same rooti in the destination fs tree: > > item 5 key (256 DIR_INDEX 9) itemoff 15967 itemsize 39 > location key (258 ROOT_ITEM 18446744073709551615) type DIR > transid 7 data_len 0 name_len 9 > name: snapshot1 > > The location key is generally used to read the root. This is not a > problem per-se since the function dealing with root searching > (btrfs_find_root) is well equipped to deal with offset being -1, namely: > > If ->offset of 'search_key' is -1ULL, it means we are not sure the > offset of the search key, just lookup the root with the highest > offset for a given objectid. > > However this is a needless inconcistency in the way internal data > structures are being created. This patch modifies the behavior so that > DIR_INDEX/DIR_ITEM will have the offset field of the location key set > to the transid. While this results in a change of the on-disk metadata, > it doesn't constitute a functional change since older kernels can cope > with both '-1' and transid as values of the offset field so no INCOMPAT > flags are needed. > > Finally while at it also move the initialization of the key in > create_pending_snapshot closer to where it's being used for the first > time. > > Signed-off-by: Nikolay Borisov Yet another ping