computing userland pointers

[drhodus at catpa.com]

Quoting "David P. Reese, Jr." <daver at 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.

What is the approximate calculation of the use frequency if this
macro if implemented ? 



-DR