On Wed, 20 Jun 2007, Andreas Dilger wrote:
> On Jun 20, 2007 11:29 -0700, [email protected] wrote:
> > This adds support for a block size of up to 64k on any platform.
> > It enables the mounting filesystems that have a larger blocksize
> > than the page size.
>
> Might have been good to CC the ext2/3/4 maintainers here? I definitely
> have been waiting for a patch like this for ages (so definitely no
> objection from me), but there are a few caveats before this will work
> on ext2/3/4.
The CC list is already big so I thought those would be monitoring
linux-fsdevel.
> > Hmmm... Actually there is nothing additional to be done after the earlier
> > cleanup of the macros. So just modify copyright.
>
> It is NOT possible to have 64kB blocksize on ext2/3/4 without some small
> 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. What is needed is to put
> 2 empty records in such a directory, or to special-case an impossible
> value like rec_len = 0xffff to handle this.
>
> There was a patch to fix the 64kB blocksize directory problem, but it
> hasn't been merged anywhere yet seeing as there wasn't previously a
> patch to allow larger blocksize...
mke2fs allows to specify a 64kb blocksize and IA64 can run with 64kb
PAGE_SIZE. So this is a bug in ext2fs that needs to be fixed regardless.
> Having 32kB blocksize has no problems that I'm aware of. Also, I'm not
> sure how it happened, but ext2 SHOULD have an explicit check (as
> ext3/4 does) limiting it to EXT2_MAX_BLOCK_SIZE. Otherwise it appears
> that there would be no error reported if the superblock reports e.g. 16MB
> blocksize, and all kinds of things would break.
mke2fs fails for blocksizes > 64k so you are safe there. I'd like to see
that limit lifted?
> There shouldn't be a problem with increasing EXT{2,3,4}_MAX_BLOCK_SIZE to
> 32kB (AFAIK), but I haven't looked into this in a while.
I'd love to see such a patch. That is also useful for arches that have
PAGE_SIZE > 4kb without this patchset.
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