This is a proposal-in-code for a substantial modification of the way

the high kernel calls into a protocol stack to perform requests on the
user's behalf.  We replace the pr_usrreq() entry in struct protosw with a
pointer to a structure containing pointers to functions which implement
the various reuqests; each function is declared with the correct type and
number of arguments.  (This is unlike the current scheme in which a quarter
of the requests take arguments of type other than (struct mbuf *) and the
difference is papered over with casts.)  There are a few benefits to this
new scheme:

1) Arguments are passed with their correct types, and null-pointer dummies
   are no longer necessary.

2) There should be slightly better caching effects from eliminating
   the prximity to extraneous code and th switch in pr_usrreq().

3) It becomes much easier to change the types of the arguments to something
   other than `struct mbuf *' (e.g.,pushing the work of sosend() into
   the protocol as advocated by Van Jacobson).

There is one principal drawback: existing protocol stacks need to
be modified.  This is alleviated by compatibility code in
uipc_socket2.c and uipc_domain.c which emulates the new interface
in terms of the old and vice versa.

This idea is not original to me.  I  read about what Jacobson did
in one of his papers and have tried to implement  the first steps
towards something like that here.  Much work remains to be done.

1 files changed, 10 insertions, 2 deletions

diff --git a/sys/kern/uipc_domain.c b/sys/kern/uipc_domain.c
index b64a44b..c989f94 100644
--- a/sys/kern/uipc_domain.c
+++ b/sys/kern/uipc_domain.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)uipc_domain.c	8.2 (Berkeley) 10/18/93
- * $Id: uipc_domain.c,v 1.11 1995/12/02 17:10:38 bde Exp $
+ * $Id: uipc_domain.c,v 1.12 1995/12/16 02:13:50 bde Exp $
  */
 
 #include <sys/param.h>
@@ -103,9 +103,17 @@ domaininit(dummy)
 	for (dp = domains; dp; dp = dp->dom_next) {
 		if (dp->dom_init)
 			(*dp->dom_init)();
-		for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++)
+		for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++){
+#ifdef PRU_OLDSTYLE
+			/* See comments in uipc_socket2.c. */
+			if (pr->pr_usrreqs == 0)
+				pr->pr_usrreqs = &pru_oldstyle;
+			else if(pr->pr_usrreq == 0)
+				pr->pr_usrreq = pr_newstyle_usrreq;
+#endif
 			if (pr->pr_init)
 				(*pr->pr_init)();
+		}
 	}
 
 	if (max_linkhdr < 16)		/* XXX */