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    SubjectRe: If not readdir() then what?
    On Thu, 12 April 2007 11:46:41 +1000, Neil Brown wrote:
    > I could argue that nfs came before ext3+dirindex, so ext3 should have
    > been designed to work properly with NFS. You could argue that fixing
    > it in nfsd fixes it for all filesystems. But I'm not sure either of
    > those arguments are likely to be at all convincing...

    Caring about a non-ext3 filesystem, I sure would like an nfs solution as
    well. :)

    > Hmmm. I wonder. Which is more likely?
    > - That two 64bit hashes from some set are the same
    > - or that 65536 48bit hashes from a set of equal size are the same.

    The former. Each bit going from hash strength to collision chain length
    reduces the likelihood of an overflow. In the extreme case of a 0bit
    hash and 64bit collision chain, you need 2^64 entries compared to 2^32
    for the other extreme.

    However, the collision chain gives me quite a bit of headache. One
    would have to store each entry's position on the chain, deal with older
    entries getting deleted, newer entries getting removed, etc. All this
    requires a lot of complicated code that basically never gets tested in
    the wild.

    Just settling for a 64bit hash and returning -EEXIST when someone causes
    a collision an creat() sounds more appealing. Directories with 4
    billion entries will cause problems, but that is hardly news to anyone.


    Fantasy is more important than knowledge. Knowledge is limited,
    while fantasy embraces the whole world.
    -- Albert Einstein
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