From: Theodore Ts'o Subject: [PATCH 11/28] ext4: correctly calculate number of blocks for fiemap Date: Tue, 2 Mar 2010 13:18:28 -0500 Message-ID: <1267553925-6308-12-git-send-email-tytso@mit.edu> References: <1267553925-6308-1-git-send-email-tytso@mit.edu> Cc: Leonard Michlmayr , "Theodore Ts'o" To: Ext4 Developers List Return-path: Received: from THUNK.ORG ([69.25.196.29]:43086 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753406Ab0CBSS6 (ORCPT ); Tue, 2 Mar 2010 13:18:58 -0500 In-Reply-To: <1267553925-6308-1-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Leonard Michlmayr ext4_fiemap() rounds the length of the requested range down to blocksize, which is 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. We fix this by calculating the last block of the region and then subtract to find the number of blocks in the extents. Signed-off-by: Leonard Michlmayr Signed-off-by: "Theodore Ts'o" --- fs/ext4/extents.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index bd80891..bc9860f 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -3768,7 +3768,6 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, __u64 start, __u64 len) { ext4_lblk_t start_blk; - ext4_lblk_t len_blks; int error = 0; /* fallback to generic here if not in extents fmt */ @@ -3782,8 +3781,11 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) { error = ext4_xattr_fiemap(inode, fieinfo); } else { + ext4_lblk_t last_blk, len_blks; + start_blk = start >> inode->i_sb->s_blocksize_bits; - len_blks = len >> inode->i_sb->s_blocksize_bits; + 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. -- 1.6.6.1.1.g974db.dirty