Re: [PATCH 2/2] ext2: Avoid rec_len overflow with 64KB block size

On Wed, 2007-10-17 at 21:09 -0700, Andrew Morton wrote:
On Thu, 11 Oct 2007 13:18:49 +0200 Jan Kara <jack@xxxxxxx> wrote:

With 64KB blocksize, a directory entry can have size 64KB which does not fit
into 16 bits we have for entry lenght. So we store 0xffff instead and convert
value when read from / written to disk.

btw, this changes ext2's on-disk format.

Just to clarify this is only changes the directory entries format on
ext2/3/4 fs with 64k block size. But currently without kernel changes
ext2/3/4 does not support 64 block size.

a) is the ext2 format documented anywhere? If so, that document will
need updating.


The e2fsprogs needs to be changed to sync up with this change.

Ted has a paper a while back to show ext2 disk format
http://web.mit.edu/tytso/www/linux/ext2intro.html

The Documentation/filesystems/ext2.txt doesn't have the ext2 format
documented. That document is out-dated need to be reviewed and cleaned
up.

b) what happens when an old ext2 driver tries to read and/or write this
directory entry? Do we need a compat flag for it?

c) what happens when old and new ext3 or ext4 try to read/write this
directory entry?


Without the first patch in this series: ext2 large blocksize support
patches, it fails to mount a ext2 filesystem with 64k block size.

[PATCH 1/2] ext2: Support large blocksize up to PAGESIZE
http://lkml.org/lkml/2007/10/1/361

So the old ext2/3/4 driver will not get access the directory entry with
64k block size format changes.


Regards,

Mingming

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