POSIX.1 semaphores vs message queues

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

I'd like to understand the rationale that makes POSIX sempahores a
non-optional component of the kernel, while POSIX message queues are
still optional.  Both seem to be related specifically to use in the
librt real-time library.

P1003_1B_SEMAPHORE option was removed about 3 1/2 years ago [1] by
Joerg, but I don't seem to see any discussion on this.  And yet, we
still have MQUEUE as an option.

Yes, MQUEUE is still automatically included by default, via
src/sys/conf/std, but it can be removed by adding 'no option MQUEUE'
to a custom kernel config.  There is no corresponding way to remove
the semaphore code from a kernel, since it is now included in the
kern 'package'.

Why is one optional/removeable, and the other required/mandatory?  Is
there some other component within the kernel that depends heavily on
the semaphore code (I've looked, but haven't found it)?


[1] http://mail-index.netbsd.org/source-changes/2012/03/10/msg032675.html

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