From aca92ff6f57c000d1b4523e383c8bd6b8269b8b1 Mon Sep 17 00:00:00 2001
From: Leonard Michlmayr <leonard.michlmayr@gmail.com>
Date: Thu, 4 Mar 2010 17:07:28 -0500
Subject: ext4: correctly calculate number of blocks for fiemap

From: Leonard Michlmayr <leonard.michlmayr@gmail.com>

commit aca92ff6f57c000d1b4523e383c8bd6b8269b8b1 upstream.

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 <leonard.michlmayr@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 fs/ext4/extents.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3767,7 +3767,6 @@ int ext4_fiemap(struct inode *inode, str
 		__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 */
@@ -3781,8 +3780,14 @@ int ext4_fiemap(struct inode *inode, str
 	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) {
 		error = ext4_xattr_fiemap(inode, fieinfo);
 	} else {
+		ext4_lblk_t len_blks;
+		__u64 last_blk;
+
 		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;
+		if (last_blk >= EXT_MAX_BLOCK)
+			last_blk = EXT_MAX_BLOCK-1;
+		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;
 
 		/*
 		 * Walk the extent tree gathering extent information.