From: Leonard Michlmayr Subject: [PATCH 2.6.32.7] ext4: number of blocks for fiemap Date: Sat, 13 Feb 2010 00:20:01 +0100 Message-ID: <1266016801.27587.13.camel@michlmayr> References: <1257360161.22057.16.camel@michlmayr> <372739E0-41AD-4DEC-9187-1396BE5894BD@sun.com> <1257371050.13852.28.camel@michlmayr> <4B701793.9010005@canonical.com> <1266000136.4310.36.camel@michlmayr> <4D0CB743-94B6-49AB-B838-BCDD2EC8C3ED@sun.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: ext4 development , "linux-kernel@vger.kernel.org Mailinglist" , 474597@bugs.launchpad.net To: Andreas Dilger Return-path: Received: from fg-out-1718.google.com ([72.14.220.158]:42441 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752979Ab0BLXUH (ORCPT ); Fri, 12 Feb 2010 18:20:07 -0500 In-Reply-To: <4D0CB743-94B6-49AB-B838-BCDD2EC8C3ED@sun.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2010-02-12, at 14:49 -0700 Andreas Dilger wrote: > If "last_blk" is only used in this one place, please put the > declaration inside the scope of the "else" clause. Looks fine > otherwise. Done. Thanks. --- 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. 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 2010-02-13 00:01:56.000000000 +0100 @@ -3725,8 +3725,11 @@ int ext4_fiemap(struct inode *inode, str if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) { error = ext4_xattr_fiemap(inode, fieinfo); } else { + ext4_lblk_t last_blk; 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.