Re: Introduce curlwp_bind and curlwp_unbind for psref(9)

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Mon, 13 Jun 2016 14:00:16 +0200
   From: Joerg Sonnenberger <joerg%bec.de@localhost>

   On Mon, Jun 13, 2016 at 07:36:31PM +0900, Ryota Ozaki wrote:
   > Currently we do it by open-coding in each place,
   > but we should provide some API to simplify codes.
   > riastradh@ suggested curlwp_bind and curlwp_unbind
   > some time ago (*1) and this patch (*2) just follows
   > the idea.

   The primary question for me is whether nesting should be allowed or not.
   That would mean a reference count behind the flag.

This `reference count' gets stored on the stack.  The caller does:

	int bound = curlwp_bind();

	... psref_wotsit ...

	curlwp_unbind(bound);

If it was already bound, bound = 1 and curlwp_unbind does nothing; if
it was not already bound, bound = 0 and curlwp_unbind unbinds it.

Perhaps the name should be `curlwp_bound_restore' or something else to
emphasize this, but I haven't come up with one that I like better on
aesthetic grounds.