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

Mingming Cao
2007-10-19T02:06:19Z

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