computing userland pointers

["David P. Reese, Jr." <daver@xxxxxxxxxxxx>]

In separating recvmsg() I want to be able to copyout to a single member of
a struct msghdr that lives in userland.  I'm currently using code like

   ucontrollenp = (socklen_t *)((caddr_t)uap->msg + offsetof(struct msghdr,
       msg_controllen));

I'm curious if anything like this already exists as a macro.  If it such
a macro doesn't exist, would there be any argument against adding one?

#define UADDRESS(cast, type, addr, member) \
	(cast)((caddr_t)addr + offsetof(type, member))

I think it could be placed in sys/systm.h.

-- 
   David P. Reese, Jr.                                     daver@xxxxxxxxxxxx
                                               http://www.gomerbud.com/daver/