linux-ext4 - [PATCH][BUG] ext4: dx_map_entry cannot support over 64KB block size

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Message-Id: <20090605165049.e8bd9c74.toshi.okajima@jp.fujitsu.com>
Date:	Fri, 5 Jun 2009 16:50:49 +0900
From:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
To:	tytso@....edu, adilger@....com
Cc:	linux-ext4@...r.kernel.org
Subject: [PATCH][BUG] ext4: dx_map_entry cannot support over 64KB block size

From: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>

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@...fujitsu.com>
---
 fs/ext4/namei.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- linux-2.6.30-rc6/fs/ext4/namei.c.orig	2009-05-26 01:35:09.000000000 +0900
+++ linux-2.6.30-rc6/fs/ext4/namei.c	2009-06-06 00:05:51.000000000 +0900
@@ -750,7 +750,7 @@ static int dx_make_map(struct ext4_dir_e
 			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();
@@ -1148,7 +1148,8 @@ dx_move_dirents(char *from, char *to, st
 	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 =
--
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