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Re: /usr/lib vs /usr/libexec

Lars Wirzenius <liw@liw.iki.fi> writes:

> I may be completely wrong here, but as far as I understand, ld turns
> -lfoo into /usr/lib/libfoo.a and then uses that if it can find it. It
> might look into some other directories as well, and it might fill in foo
> into some other patterns than "lib%s.a", but basically that is it. It
> does not scan the /usr/lib directory, it merely looks up a filename it
> knows already.

Right, and "open" is O(n) on just about every system.  If that's not
true on ext2, then that's good news, and I'm surprised.

> With modern filesystems, the kernel also does not need to read through
> the entires /usr/lib directory listing: modern filesystems user B-trees
> or other ways to speed up filename lookups. O(log n), that is, or even
> approximately O(1) if a good hash is used.

Actually, even systems as old as ITS used better than O(n)
directories.  It's Unix that has historically stunk.  It's not a
modern/old thing, it's a Just Do It thing. 

Which Linux filesystems have better than O(n) performance on open?


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