ext3: support large blocksize up to PAGESIZE

This patch set supports large block size(>4k, <=64k) in ext3 just enlarging
the block size limit.  But it is NOT possible to have 64kB blocksize on
ext3 without some changes to the directory handling code.  The reason is
that an empty 64kB directory block would have a rec_len == (__u16)2^16 ==
0, and this would cause an error to be hit in the filesystem.  The proposed
solution is treat 64k rec_len with a an impossible value like rec_len =
0xffff to handle this.

The Patch-set consists of the following 2 patches.
  [1/2]  ext3: enlarge blocksize
         - Allow blocksize up to pagesize

  [2/2]  ext3: fix rec_len overflow
         - prevent rec_len from overflow with 64KB blocksize

Now on 64k page ppc64 box runs with this patch set we could create a 64k
block size ext3, and able to handle empty directory block.

Signed-off-by: Takashi Sato <sho@tnes.nec.co.jp>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>