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 AD780C3F2D9 for ; Tue, 3 Mar 2020 17:19:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 858C120863 for ; Tue, 3 Mar 2020 17:19:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729810AbgCCRT2 (ORCPT ); Tue, 3 Mar 2020 12:19:28 -0500 Received: from mx2.suse.de ([195.135.220.15]:37290 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728615AbgCCRT2 (ORCPT ); Tue, 3 Mar 2020 12:19:28 -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 CDF1CAC65; Tue, 3 Mar 2020 17:19:25 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 2D5C3DA7AE; Tue, 3 Mar 2020 18:19:03 +0100 (CET) Date: Tue, 3 Mar 2020 18:19:02 +0100 From: David Sterba To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org, Johannes Thumshirn Subject: Re: [PATCH v2 01/10] btrfs: backref: Introduce the skeleton of btrfs_backref_iter Message-ID: <20200303171902.GI2902@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org, Johannes Thumshirn References: <20200302094553.58827-1-wqu@suse.com> <20200302094553.58827-2-wqu@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200302094553.58827-2-wqu@suse.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Mar 02, 2020 at 05:45:44PM +0800, 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; > + } > + 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; What's the reason for ENOTTY? > + goto release; > + } > + iter->cur_ptr = iter->item_ptr + sizeof(*ei); > + > + /* If there is no inline backref, go search for keyed backref */ > + if (iter->cur_ptr >= iter->end_ptr) { > + ret = btrfs_next_item(fs_info->extent_root, path); > + > + /* No inline nor keyed ref */ > + if (ret > 0) { > + ret = -ENOENT; > + goto release; > + } > + if (ret < 0) > + goto release; > + > + btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key, > + path->slots[0]); > + if (iter->cur_key.objectid != bytenr || > + (iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY && > + iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY)) { > + ret = -ENOENT; > + goto release; > + } > + iter->cur_ptr = btrfs_item_ptr_offset(path->nodes[0], > + path->slots[0]); > + iter->item_ptr = iter->cur_ptr; > + iter->end_ptr = iter->item_ptr + btrfs_item_size_nr( > + path->nodes[0], path->slots[0]); > + } > + > + return 0; > +release: > + btrfs_backref_iter_release(iter); > + return ret; > +} > diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h > index 777f61dc081e..8b1ec11d4b28 100644 > --- a/fs/btrfs/backref.h > +++ b/fs/btrfs/backref.h > @@ -74,4 +74,64 @@ struct prelim_ref { > u64 wanted_disk_byte; > }; > > +/* > + * Helper structure to help iterate backrefs of one extent. > + * > + * Now it only supports iteration for tree block in commit root. > + */ > +struct btrfs_backref_iter { > + u64 bytenr; > + struct btrfs_path *path; > + struct btrfs_fs_info *fs_info; > + struct btrfs_key cur_key; > + unsigned long item_ptr; > + unsigned long cur_ptr; > + unsigned long end_ptr; > +}; > + > +static inline struct btrfs_backref_iter * > +btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info, gfp_t gfp_flag) This does not need to be static inline, and please keep the type and function name on the same line. > +{ > + struct btrfs_backref_iter *ret; > + > + ret = kzalloc(sizeof(*ret), gfp_flag); > + if (!ret) > + return NULL; > + > + ret->path = btrfs_alloc_path(); > + if (!ret) { > + kfree(ret); > + return NULL; > + } > + > + /* Current backref iterator only supports iteration in commit root */ > + ret->path->search_commit_root = 1; > + ret->path->skip_locking = 1; > + ret->path->reada = READA_FORWARD; > + ret->fs_info = fs_info; > + > + return ret; > +}