ext3: Fix support for empty directory blocks in 64k blocksize filesystems

The rec_len field in the directory entry is 16 bits, so if the filesystem is completely empty, rec_len of 0 is used to designate 65536 in e2fsprogs, for the case where the directory entry takes the entire 64k block.

But if empty directory is read, error message will be output by current kernel. You can do the following commands to reproduct it.

- mkfs.ext3 -b $(( 64 * 1024 )) /dev/sdc1
- mount /dev/sda1 /mnt
- cd /mnt/lost+found
- ll
- tail /var/log/messages
EXT3-fs error (device sdc1): ext3_readdir: bad entry in \
directory #11: rec_len is smaller than minimal - offset=0, \
inode=0, rec_len=0, name_len=0

This patch fix to treat rec_len of 0 as 65536, like what e2fsprogs do.

---
 include/linux/ext3_fs.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

index dd495b8..dc975ad 100644
@@ -711,7 +711,7 @@ static inline unsigned ext3_rec_len_from_disk(__le16 dlen)
 {
 	unsigned len = le16_to_cpu(dlen);
 
-	if (len == EXT3_MAX_REC_LEN)
+	if (len == EXT3_MAX_REC_LEN || len == 0)
 		return 1 << 16;
 	return len;
 }

@@ -719,7 +719,7 @@ static inline unsigned ext3_rec_len_from_disk(__le16 dlen)
 static inline __le16 ext3_rec_len_to_disk(unsigned len)
 {
 	if (len == (1 << 16))
-		return cpu_to_le16(EXT3_MAX_REC_LEN);
+		return cpu_to_le16(0);
 	else if (len > (1 << 16))
 		BUG();
 	return cpu_to_le16(len);

1.5.3.8