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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 CFC53C3F2CD for ; Wed, 4 Mar 2020 07:41:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5F1B207FD for ; Wed, 4 Mar 2020 07:41:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728458AbgCDHl4 (ORCPT ); Wed, 4 Mar 2020 02:41:56 -0500 Received: from mx2.suse.de ([195.135.220.15]:39778 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728301AbgCDHl4 (ORCPT ); Wed, 4 Mar 2020 02:41:56 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 580E0AF19; Wed, 4 Mar 2020 07:41:53 +0000 (UTC) Subject: Re: [PATCH v2 01/10] btrfs: backref: Introduce the skeleton of btrfs_backref_iter To: Qu Wenruo , linux-btrfs@vger.kernel.org Cc: Johannes Thumshirn References: <20200302094553.58827-1-wqu@suse.com> <20200302094553.58827-2-wqu@suse.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <668ee0c8-9b76-df7a-026e-8ff056b46025@suse.com> Date: Wed, 4 Mar 2020 09:41:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200302094553.58827-2-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2.03.20 г. 11:45 ч., Qu Wenruo wrote: > Due to the complex nature of btrfs extent tree, when we want to iterate > all backrefs of one extent, it involves quite a lot of work, like > searching the EXTENT_ITEM/METADATA_ITEM, iteration through inline and keyed > backrefs. > > Normally this would result pretty complex code, something like: > btrfs_search_slot() > /* Ensure we are at EXTENT_ITEM/METADATA_ITEM */ > while (1) { /* Loop for extent tree items */ > while (ptr < end) { /* Loop for inlined items */ > /* REAL WORK HERE */ > } > next: > ret = btrfs_next_item() > /* Ensure we're still at keyed item for specified bytenr */ > } > > The idea of btrfs_backref_iter is to avoid such complex and hard to > read code structure, but something like the following: > > iter = btrfs_backref_iter_alloc(); > ret = btrfs_backref_iter_start(iter, bytenr); > if (ret < 0) > goto out; > for (; ; ret = btrfs_backref_iter_next(iter)) { > /* REAL WORK HERE */ > } > out: > btrfs_backref_iter_free(iter); > > This patch is just the skeleton + btrfs_backref_iter_start() code. > > Signed-off-by: Qu Wenruo > Reviewed-by: Johannes Thumshirn > --- > fs/btrfs/backref.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++ > fs/btrfs/backref.h | 60 ++++++++++++++++++++++++++++++++ > 2 files changed, 147 insertions(+) > > diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c > index 327e4480957b..444cd5d31d87 100644 > --- a/fs/btrfs/backref.c > +++ b/fs/btrfs/backref.c > @@ -2299,3 +2299,90 @@ void free_ipath(struct inode_fs_paths *ipath) > kvfree(ipath->fspath); > kfree(ipath); > } > + > +int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr) > +{ > + struct btrfs_fs_info *fs_info = iter->fs_info; > + struct btrfs_path *path = iter->path; > + struct btrfs_extent_item *ei; > + struct btrfs_key key; > + int ret; > + > + key.objectid = bytenr; > + key.type = BTRFS_METADATA_ITEM_KEY; > + key.offset = (u64)-1; > + iter->bytenr = bytenr; > + > + ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0); > + if (ret < 0) > + return ret; > + if (ret == 0) { > + ret = -EUCLEAN; > + goto release; > + } > + if (path->slots[0] == 0) { > + WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG)); > + ret = -EUCLEAN; > + goto release; > + } > + path->slots[0]--; > + > + btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]); > + if (!(key.type == BTRFS_EXTENT_ITEM_KEY || > + key.type == BTRFS_METADATA_ITEM_KEY) || key.objectid != bytenr) { > + ret = -ENOENT; > + goto release; > + } nit: Please keep the logic of the checks identical as it makes comprehending the code easier. What I mean is here you do !(type == COND1 || type == COND2) which really translates to type != COND && type != COND2. However, when checking for keyed items you use the second style. Yes, they are both identical in terms of semantics but one might wonder "why is this done in 2 different ways for no apparent reason" ? > + memcpy(&iter->cur_key, &key, sizeof(key)); > + iter->item_ptr = btrfs_item_ptr_offset(path->nodes[0], > + path->slots[0]); > + iter->end_ptr = iter->item_ptr + btrfs_item_size_nr(path->nodes[0], > + path->slots[0]); > + ei = btrfs_item_ptr(path->nodes[0], path->slots[0], > + struct btrfs_extent_item); > + > + /* > + * Only support iteration on tree backref yet. > + * > + * This is extra precaustion for non skinny-metadata, where > + * EXTENT_ITEM is also used for tree blocks, that we can only use > + * extent flags to determine if it's a tree block. > + */ > + if (btrfs_extent_flags(path->nodes[0], ei) & BTRFS_EXTENT_FLAG_DATA) { > + ret = -ENOTTY; why not simply -ENOSUPP > + goto release; > + }