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    SubjectRe: [36/37] Large blocksize support for ext2
    On Jun 20, 2007  14:27 -0700, Christoph Lameter wrote:
    > > > 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.

    True. I had increased the e2fsprogs blocksize to 16kB after testing it,
    and after that it seems Ted increased it to 64kB after that. The 64kB
    directory problem only came out recently.

    > > 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?

    I don't think extN can go to past 64kB blocksize in any case.

    > > 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.

    Definitely, which is why we had been working on this originally.

    Cheers, Andreas
    Andreas Dilger
    Principal Software Engineer
    Cluster File Systems, Inc.

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