[PATCH] Make AIO conditional on actual need

Amos Jeffries wrote:
> To fix OpenBSD current build issues we need to resolve one of the older
> TODO items:
>
> TODO: Detect AIO support cleanly.
>
> Requires some shuffling + rewrite of configure.in to get this sequence:
>
> - detect AIO header + libraries usability
> - for each component that depends on it...
> - if auto-enabled and AIO missing. auto-disable instead.
> - if force-enabled. error message on missing AIO
> - else enable, and set needs_aio
> - if needs_aio after all that
> - define the AIO include and libraries ac_define/ac_subst
>
> Q: Is the --with-aio option still useful after that change?
> A: Yes Gentoo will probably need it to pull libaio in for the build. But
> it's a non-op for everyone else.
>
> I want to get it done shortly, but have other stuff on the plate. If
> anyone else has time please yell out and give it a go.
>

So I did find the time anyways...

Attached is a patch which seeks to do the above logics. With the result
that AIO is only enabled when actualy needed and available.

 From what I could tell of the existing stuff in configure.in its likely
that COSS was the only reason to use AIO. So this is effectively
disabling AIO in Squid-3.

If anyone knows of another component needing or even making use of POSIX
AIO this patch will need adjusting to mark that need.

I have not counted AUFS use of AIO since that seems to be done
separately via DiskThreads and AIOPS.

Amos

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