ext4_fiemap gives 0 extents for files smaller than a block (patchincluded)

[Leonard Michlmayr]

Fiemap (ioctl) does not return any extents for small files on ext4.
(fm_start=0, fm_length=filesize)

File affected: fs/ext4/extents.c

I found the reason of the bug: wrong rounding. It will not only affect
small files, but any request that overlaps an extent boundary by less
that blocksize.

The attached patch is against 2.6.32-rc5.

Leonard Michlmayr

diff -Naur linux-2.6.32-rc5/fs/ext4/extents.c linux-2.6.32-rc5.patched/fs/ext4/extents.c
--- linux-2.6.32-rc5/fs/ext4/extents.c	2009-10-16 02:41:50.000000000 +0200
+++ linux-2.6.32-rc5.patched/fs/ext4/extents.c	2009-11-04 19:35:44.000000000 +0100
@@ -3685,6 +3685,7 @@
 		__u64 start, __u64 len)
 {
 	ext4_lblk_t start_blk;
+	ext4_lblk_t end_blk;
 	ext4_lblk_t len_blks;
 	int error = 0;
 
@@ -3700,7 +3701,8 @@
 		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;
+		end_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
+		len_blks = end_blk - start_blk + 1;
 
 		/*
 		 * Walk the extent tree gathering extent information.