From: Leonard Michlmayr Subject: [PATCH 2.6.32.7] ext4: number of blocks for fiemap Date: Fri, 12 Feb 2010 19:42:16 +0100 Message-ID: <1266000136.4310.36.camel@michlmayr> References: <1257360161.22057.16.camel@michlmayr> <372739E0-41AD-4DEC-9187-1396BE5894BD@sun.com> <1257371050.13852.28.camel@michlmayr> <4B701793.9010005@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: surbhi.palande@canonical.com, linux-kernel@vger.kernel.org, 474597@bugs.launchpad.net To: linux-ext4@vger.kernel.org Return-path: Received: from mail-fx0-f220.google.com ([209.85.220.220]:55190 "EHLO mail-fx0-f220.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752811Ab0BLSmX (ORCPT ); Fri, 12 Feb 2010 13:42:23 -0500 In-Reply-To: <4B701793.9010005@canonical.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Problem: fs/ext4/extents.c:ext4_fiemap rounds the length of the requested range down to blocksize. This is not the true number of blocks that cover the requested region. This problem is especially impressive if the user requests only the first byte of a file: not a single extent will be reported. Solution: Calculate the last byte of the region and round to blocksize. Then get the number of blocks by subtracting last_blk - start_blk and adding 1 for the first block. (The variable last_blk is introduced just for easier reading.) This patch will fix this. I already suggested this patch some time ago, this is the same patch for a more recent kernel version. Signed-off-by: Leonard Michlmayr diff -rup linux-2.6.32.7/fs/ext4/extents.c linux-2.6.32.7-lm/fs/ext4/extents.c --- linux-2.6.32.7/fs/ext4/extents.c 2010-01-29 00:06:20.000000000 +0100 +++ linux-2.6.32.7-lm/fs/ext4/extents.c 2010-02-11 21:26:40.000000000 +0100 @@ -3711,6 +3711,7 @@ int ext4_fiemap(struct inode *inode, str __u64 start, __u64 len) { ext4_lblk_t start_blk; + ext4_lblk_t last_blk; ext4_lblk_t len_blks; int error = 0; @@ -3726,7 +3727,9 @@ int ext4_fiemap(struct inode *inode, str error = ext4_xattr_fiemap(inode, fieinfo); } else { start_blk = start >> inode->i_sb->s_blocksize_bits; - len_blks = len >> inode->i_sb->s_blocksize_bits; + /* the last byte in the range is (start + len - 1) */ + last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits; + len_blks = last_blk - start_blk + 1; /* * Walk the extent tree gathering extent information.