From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:56912 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752100AbeEQG2I (ORCPT ); Thu, 17 May 2018 02:28:08 -0400 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: jamespharvey20@gmail.com Subject: [PATCH 2/4] btrfs: lzo: Add comment about the how btrfs records its lzo compressed data Date: Thu, 17 May 2018 14:27:51 +0800 Message-Id: <20180517062753.25973-3-wqu@suse.com> In-Reply-To: <20180517062753.25973-1-wqu@suse.com> References: <20180517062753.25973-1-wqu@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Signed-off-by: Qu Wenruo --- fs/btrfs/lzo.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c index 0667ea07f766..3d2ae4c08876 100644 --- a/fs/btrfs/lzo.c +++ b/fs/btrfs/lzo.c @@ -17,6 +17,29 @@ #define LZO_LEN 4 +/* + * Btrfs LZO compression format + * + * Regular LZO compressed data extent is consist of: + * 1. Header + * Fixed size. LZO_LEN (4) bytes long, LE16. + * Records the total size (*includes* the header) of real compressed data. + * + * 2. Segment(s) + * Variable size. Includes one segment header, and then data payload. + * One btrfs compressed data can have one or more segments. + * + * 2.1 Segment header + * Fixed size. LZO_LEN (4) bytes long, LE16. + * Records the total size of the segment (*excludes* the header). + * + * 2.2 Data Payload + * Variable size. Size up limit should be lzo1x_worst_compress(PAGE_SIZE). + * + * While for inlined LZO compressed data extent, it doesn't have Header, just + * one Segment. + */ + struct workspace { void *mem; void *buf; /* where decompressed data goes */ -- 2.17.0