ext4: fix dx_map_entry to support 256k directory blocks

The dx_map_entry structure doesn't support over 64KB block size by
current usage of its member("offs"). Because "offs" treats an offset
of copies of the ext4_dir_entry_2 structure as is. This member size is
16 bits. But real offset for over 64KB(256KB) block size needs 18
bits. However, real offset keeps 4 byte boundary, so lower 2 bits is
not used.

Therefore, we do the following to fix this limitation:
For "store": 
	we divide the real offset by 4 and then store this result to "offs" 
	member.
For "use":
	we multiply "offs" member by 4 and then use this result 
	as real offset.

Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index f2bc160463b7..07eb6649e4fa 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -749,7 +749,7 @@ static int dx_make_map(struct ext4_dir_entry_2 *de, unsigned blocksize,
                         ext4fs_dirhash(de->name, de->name_len, &h);
                         map_tail--;
                         map_tail->hash = h.hash;
-                        map_tail->offs = (u16) ((char *) de - base);
+                        map_tail->offs = ((char *) de - base)>>2;
                         map_tail->size = le16_to_cpu(de->rec_len);
                         count++;
                         cond_resched();
@@ -1147,7 +1147,8 @@ dx_move_dirents(char *from, char *to, struct dx_map_entry *map, int count,
         unsigned rec_len = 0;
 
         while (count--) {
-                struct ext4_dir_entry_2 *de = (struct ext4_dir_entry_2 *) (from + map->offs);
+                struct ext4_dir_entry_2 *de = (struct ext4_dir_entry_2 *) 
+                                                (from + (map->offs<<2));
                 rec_len = EXT4_DIR_REC_LEN(de->name_len);
                 memcpy (to, de, rec_len);
                 ((struct ext4_dir_entry_2 *) to)->rec_len =