First draft: rewrite of {get|set|swap}context(3)

[Daniel Eischen]

On Sun, 17 Aug 2003, Marcel Moolenaar wrote:

> Gang,
> 
> Please review the attached patch and let me know to what extend it
> introduces breakages. It is the result of "aggressive engineering"
> to provoke comments and further fuel discussion. The reason for this
> approach is that we currently do not initialize any fields other than
> the mcontext and sigmask and only partially copyin() and copyout()
> the contexts (typically only the mcontext and sigmask fields). This
> generally is very sensitive to breakages, especially when we intro-
> duce flags or need to use any of the spare fields.
> 
> getcontext(3): the whole ucontext is zeroed before (partially) filled
> 	and we copyout() all of it. This means that uc_link can only
> 	be set/defined after calling setcontext().

This prevents reuse of the same context without resetting
uc_link after every usage.  I don't see any requirement
by POSIX that uc_link be left intact after getcontext(),
but it might be worth preserving...  It's up to you.

Other than that, the patch looks good.

-- 
Dan Eischen