I've been struggling with setting a socket option for multicast (as suggested by pages including and similar to):

But for some reason, can't seem to get the call to setsockopt (using either the version internal to sbcl or my own define-foreign-routine version) to work without returning EINVAL and a note about one of the parameters being invalid.

This is on the latest GIT version of sbcl,, on Mac OSX x86-64.

Here's the test code:

I suspect I've misunderstood something about the sb-alien stuff, but just can't figure out what from the docs.  Anyone have any clue where I might be messing up?