Messages in this thread | | | Date | Thu, 12 Apr 2007 04:37:12 +0200 | From | Jörn Engel <> | Subject | Re: If not readdir() then what? |
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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.
Jörn
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