From patchwork Wed Apr 3 23:41:59 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qu Wenruo X-Patchwork-Id: 13616827 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3FF5515920B for ; Wed, 3 Apr 2024 23:42:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712187740; cv=none; b=u1n3rxBWVRyYps/TGt7TRMiEn3jSzBXSoh0mjt21vnTiQjTvXObD5d2nz7A1OE998QZnZR04VBaq1wLqdqNtlrG70agF4hIFz9oM7+SgJXFe+QO0u1sRceyDPPxDSPw95y39XNC7Gv1IXaXqhGt/9T/nQvLSjSFEC26byUKHgeg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712187740; c=relaxed/simple; bh=Ro7hE4VUsJPLfFkiXY8/dnlqWKCOzAOmItOzA+J0UmA=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UwjAHjtzggn1RKM+S/VykVAug1ifu1nfWFOxCeAUmkQhV9785CzBrkbVsxApWNpndMBe4YWqqil95WCc6KEcYqykfFeQZtxhUWX6RqUcxq/wXpbqmGkTz6IMtawo/g0BX6OZzcDzAcC5yVkLUESGb5b2wqQKy7ldWjL4uT8tXaA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b=TCXSPcEG; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="TCXSPcEG" Received: from imap2.dmz-prg2.suse.org (imap2.dmz-prg2.suse.org [10.150.64.98]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 812295D2E9 for ; Wed, 3 Apr 2024 23:42:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1712187736; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ewwPa6FpyyaCp0GPc93wSPwcCdvCNpINfOlw2+4tJl4=; b=TCXSPcEGcqE0dh3MJuJKdImjlTvvRw84e7UrAVFL07J0afBZgR5/YHS9OGo+vzzfVEjGfV +u1ZLnJzbdOY7noAT4h56qYqa3uZRK3lNL4Ha4m6Rw/H34QRQBqvqfxAt7QAnQf0Bia4pp AfKjD+DR/5BZ+O4P1QW83MxlgZqjPJ0= Authentication-Results: smtp-out2.suse.de; none Received: from imap2.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap2.dmz-prg2.suse.org (Postfix) with ESMTPS id AB4431331E for ; Wed, 3 Apr 2024 23:42:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap2.dmz-prg2.suse.org with ESMTPSA id WE+RF1fpDWalfQAAn2gu4w (envelope-from ) for ; Wed, 03 Apr 2024 23:42:15 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Subject: [PATCH v2 2/4] btrfs: add extra comments on extent_map members Date: Thu, 4 Apr 2024 10:11:59 +1030 Message-ID: <98da90ba55445f69030a7664ae5029d710e4efbd.1712187452.git.wqu@suse.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam-Score: 1.77 X-Spamd-Result: default: False [1.77 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; R_MISSING_CHARSET(2.50)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[linux-btrfs@vger.kernel.org]; BROKEN_CONTENT_TYPE(1.50)[]; RCPT_COUNT_ONE(0.00)[1]; NEURAL_HAM_LONG(-1.00)[-1.000]; RCVD_COUNT_THREE(0.00)[3]; TO_DN_NONE(0.00)[]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; MID_CONTAINS_FROM(1.00)[]; NEURAL_SPAM_SHORT(0.87)[0.289]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%] X-Spam-Level: * X-Spam-Flag: NO The extent_map structure is very critical to btrfs, as it is involved for both read and write paths. Unfortunately the structure is not properly explained, making it pretty hard to understand nor to do further improvement. This patch adds extra comments explaining the major members based on my code reading. Hopefully we can find more members to cleanup in the future. Signed-off-by: Qu Wenruo --- fs/btrfs/extent_map.h | 54 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 53 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h index 10e9491865c9..82768288c6da 100644 --- a/fs/btrfs/extent_map.h +++ b/fs/btrfs/extent_map.h @@ -35,19 +35,71 @@ enum { }; /* + * This structure represents file extents and holes. + * * Keep this structure as compact as possible, as we can have really large * amounts of allocated extent maps at any time. */ struct extent_map { struct rb_node rb_node; - /* all of these are in bytes */ + /* All of these are in bytes. */ + + /* File offset matching the offset of a BTRFS_EXTENT_ITEM_KEY key. */ u64 start; + + /* + * Length of the file extent. + * + * For non-inlined file extents it's btrfs_file_extent_item::num_bytes. + * For inline extents it's sectorsize, since inline data starts at + * offsetof(struct , disk_bytenr) thus + * btrfs_file_extent_item::num_bytes is not valid. + */ u64 len; + + /* + * The file offset of the original file extent before splitting. + * + * This is an in-memory only member, matching + * extent_map::start - btrfs_file_extent_item::offset for + * regular/preallocated extents. EXTENT_MAP_HOLE otherwise. + */ u64 orig_start; + + /* + * The full on-disk extent length, matching + * btrfs_file_extent_item::disk_num_bytes. + */ u64 orig_block_len; + + /* + * The decompressed size of the whole on-disk extent, matching + * btrfs_file_extent_item::ram_bytes. + * + * For non-compressed extents, this matches orig_block_len. + */ u64 ram_bytes; + + /* + * The on-disk logical bytenr for the file extent. + * + * For compressed extents it matches btrfs_file_extent_item::disk_bytenr. + * For uncompressed extents it matches + * btrfs_file_extent_item::disk_bytenr + btrfs_file_extent_item::offset + * + * For holes it is EXTENT_MAP_HOLE and for inline extents it is + * EXTENT_MAP_INLINE. + */ u64 block_start; + + /* + * The on-disk length for the file extent. + * + * For compressed extents it matches btrfs_file_extent_item::disk_num_bytes. + * For uncompressed extents it matches extent_map::len. + * For holes and inline extents it's -1 and shouldn't be used. + */ u64 block_len; /*