Simplify the way of attaching IPv6 link-layer header.

Problem description:
How do we currently perform layer 2 resolution and header imposition:

For IPv4 we have the following chain:
  ip_output() -> (ether|atm|whatever)_output() -> arpresolve()

Lookup is done in proper place (link-layer output routine) and it is possible
  to provide cached lle data.

For IPv6 situation is more complex:
  ip6_output() -> nd6_output() -> nd6_output_ifp() -> (whatever)_output() ->
    nd6_storelladdr()

We have ip6_ouput() which calls nd6_output() instead of link output routine.
nd6_output() does the following:
  * checks if lle exists, creates it if needed (similar to arpresolve())
  * performes lle state transitions (similar to arpresolve())
  * calls nd6_output_ifp() which pushes packets to link output routine along
    with running SeND/MAC hooks regardless of lle state
    (e.g. works as run-hooks placeholder).

After that, iface output routine like ether_output() calls nd6_storelladdr()
  which performs lle lookup once again.

As a result, we perform lookup twice for each outgoing packet for most types
  of interfaces. We also need to maintain runtime-checked table of 'nd6-free'
  interfaces (see nd6_need_cache()).

Fix this behavior by eliminating first ND lookup. To be more specific:
  * make all nd6_output() consumers use nd6_output_ifp() instead
  * rename nd6_output[_slow]() to nd6_resolve_[slow]()
  * convert nd6_resolve() and nd6_resolve_slow() to arpresolve() semantics,
    e.g. copy L2 address to buffer instead of pushing packet towards lower
    layers
  * Make all nd6_storelladdr() users use nd6_resolve()
  * eliminate nd6_storelladdr()

The resulting callchain is the following:
  ip6_output() -> nd6_output_ifp() -> (whatever)_output() -> nd6_resolve()

Error handling:
Currently sending packet to non-existing la results in ip6_<output|forward>
  -> nd6_output() -> nd6_output _lle() which returns 0.
In new scenario packet is propagated to <ether|whatever>_output() ->
  nd6_resolve() which will return EWOULDBLOCK, and that result
  will be converted to 0.

(And EWOULDBLOCK is actually used by IB/TOE code).

Sponsored by:		Yandex LLC
Differential Revision:	https://reviews.freebsd.org/D1469

1 files changed, 4 insertions, 7 deletions

diff --git a/sys/netinet6/nd6.h b/sys/netinet6/nd6.h
index 52bc97fef8e7..41df9e4b7341 100644
--- a/sys/netinet6/nd6.h
+++ b/sys/netinet6/nd6.h
@@ -414,22 +414,19 @@ void nd6_llinfo_settimer_locked(struct llentry *, long);
 void nd6_timer(void *);
 void nd6_purge(struct ifnet *);
 void nd6_nud_hint(struct rtentry *, struct in6_addr *, int);
-int nd6_resolve(struct ifnet *, struct rtentry *, struct mbuf *,
-	struct sockaddr *, u_char *);
+int nd6_resolve(struct ifnet *, int, struct mbuf *,
+    const struct sockaddr *, u_char *, uint32_t *);
 int nd6_ioctl(u_long, caddr_t, struct ifnet *);
 void nd6_cache_lladdr(struct ifnet *, struct in6_addr *,
 	char *, int, int, int);
-int nd6_output(struct ifnet *, struct ifnet *, struct mbuf *,
-	struct sockaddr_in6 *, struct rtentry *);
 void nd6_grab_holdchain(struct llentry *, struct mbuf **,
     struct sockaddr_in6 *);
 int nd6_flush_holdchain(struct ifnet *, struct ifnet *, struct mbuf *,
     struct sockaddr_in6 *);
-int nd6_need_cache(struct ifnet *);
 int nd6_add_ifa_lle(struct in6_ifaddr *);
 void nd6_rem_ifa_lle(struct in6_ifaddr *, int);
-int nd6_storelladdr(struct ifnet *, struct mbuf *,
-	const struct sockaddr *, u_char *, uint32_t *); 
+int nd6_output_ifp(struct ifnet *, struct ifnet *, struct mbuf *,
+    struct sockaddr_in6 *);
 
 /* nd6_nbr.c */
 void nd6_na_input(struct mbuf *, int, int);