[rfc, patch 0/3] larger block group descriptors

hello,

as recently pointed out by Andreas, there isn't enough room in the block
group descriptor structure for all the fields we want to add in order to
extend the ext3 file system and/or to add new features.

The attached patch addresses this problem, by allowing larger descriptor
sizes. The descriptor size is stored in the super-block, it must be a power
of 2, greater than or equal to 32 bytes (size of the current ext3_group_desc
structure) and must fit in one block.

Temporary, i've added a new EXT3_FEATURE_INCOMPAT_DESC_SIZE feature. If
large descriptors are used by other patches we could just merge them and use
the same incompat feature.

There are 3 diffs:

[1/3 linux_desc_size] 

	make linux-2.6.16.19 use variable length descriptors. 

[2/3 e2fsprogs_desc_size]

	make e2fsprogs-1.39 use variable length descriptors. mke2fs,
	debugfs, dumpe2fs and fsck should work.

[3/3 mkfs_opt]

	add to mke2fs a new '-D' option that specifies the descriptor size. 
	This patch is for testing purposes only; indeed we need to create a
	file system in order to test the above patches :-)

cheers, 

-- 
Alexandre