ext4: correctly calculate number of blocks for fiemap

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>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index bd808915ad2fee5f177e97b57cc35443b70e19de..7d54850f7136ee79d047cf4f313206398141bc17 100644 (file)
--- 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 +3781,14 @@ 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 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.