Allow specifying resource in posix_getrlimit() for single result

[iluuu1994]

Fetching all resource limits seems incredibly wasteful, and the API also becomes more awkward (posix_getrlimit()['soft core']). This PR allows specifying a resource, returning [$softLimit, $hardLimit] that can be destructured.

[cmb69]

This looks like a useful feature to me. I'm not quite sure, though, about the "unlimited" return value; while that matches what we have so far, yielding null might be more reasonable (after all, there is no limit).

[iluuu1994]

@cmb69 I've thought about this as well and thought it might be better to stay consistent in terms of values returned. Returning two distinct values for unlimited within the same function might be a bit of a WTF. If we do use a different value it might make more sense to return RLIM_INFINITY and expose that as a userland constant (since that can't be interpreted as a valid resource limit by the set function).

If we really want to do that, I think it might be better to introduce a new function altogether.

[iluuu1994]

Any ideas for a new function name? posix_get_single_rlimit? I couldn't come up with anything sensible, since the good name is already taken 😛 (it also really should be called getrlimits)

[cmb69]

Any ideas for a new function name?

I don't think a new function is necessary (my reaction was because you're reasoning to just return "unlimited"). IMO, this is good as is. But if we want to bikeshed, we should do this on internals. :)

[iluuu1994]

@cmb69 Do you think this needs a mail to the internals?

[cmb69]

Do you think this needs a mail to the internals?

No. But it needs an entry in UPGRADING. :)