lltable: Add support for "child" LLEs holding encap for IPv4oIPv6 entries.

Currently we use pre-calculated headers inside LLE entries as prepend data
 for `if_output` functions. Using these headers allows saving some
 CPU cycles/memory accesses on the fast path.

However, this approach makes adding L2 header for IPv4 traffic with IPv6
 nexthops more complex, as it is not possible to store multiple
 pre-calculated headers inside lle. Additionally, the solution space is
 limited by the fact that PCB caching saves LLEs in addition to the nexthop.

Thus, add support for creating special "child" LLEs for the purpose of holding
 custom family encaps and store mbufs pending resolution. To simplify handling
 of those LLEs, store them in a linked-list inside a "parent" (e.g. normal) LLE.
 Such LLEs are not visible when iterating LLE table. Their lifecycle is bound
 to the "parent" LLE - it is not possible to delete "child" when parent is alive.
 Furthermore, "child" LLEs are static (RTF_STATIC), avoding complex state
 machine used by the standard LLEs.

nd6_lookup() and nd6_resolve() now accepts an additional argument, family,
 allowing to return such child LLEs. This change uses `LLE_SF()` macro which
 packs family and flags in a single int field. This is done to simplify merging
 back to stable/. Once this code lands, most of the cases will be converted to
 use a dedicated `family` parameter.

Differential Revision: https://reviews.freebsd.org/D31379
MFC after:	2 weeks

1 files changed, 5 insertions, 1 deletions

diff --git a/sys/netinet6/nd6_nbr.c b/sys/netinet6/nd6_nbr.c
index 974c454e93a5..30d73f9d71a9 100644
--- a/sys/netinet6/nd6_nbr.c
+++ b/sys/netinet6/nd6_nbr.c
@@ -630,6 +630,7 @@ nd6_na_input(struct mbuf *m, int off, int icmp6len)
 	size_t linkhdrsize;
 	int flags, is_override, is_router, is_solicited;
 	int lladdr_off, lladdrlen, checklink;
+	bool flush_holdchain = false;
 
 	NET_EPOCH_ASSERT();
 
@@ -747,7 +748,7 @@ nd6_na_input(struct mbuf *m, int off, int icmp6len)
 	 * If no neighbor cache entry is found, NA SHOULD silently be
 	 * discarded.
 	 */
-	ln = nd6_lookup(&taddr6, LLE_EXCLUSIVE, ifp);
+	ln = nd6_lookup(&taddr6, LLE_SF(AF_INET6, LLE_EXCLUSIVE), ifp);
 	if (ln == NULL) {
 		goto freeit;
 	}
@@ -773,6 +774,7 @@ nd6_na_input(struct mbuf *m, int off, int icmp6len)
 		if (!nd6_try_set_entry_addr(ifp, ln, lladdr))
 			goto freeit;
 
+		flush_holdchain = true;
 		EVENTHANDLER_INVOKE(lle_event, ln, LLENTRY_RESOLVED);
 		if (is_solicited)
 			nd6_llinfo_setstate(ln, ND6_LLINFO_REACHABLE);
@@ -899,6 +901,8 @@ nd6_na_input(struct mbuf *m, int off, int icmp6len)
 
 	if (chain != NULL)
 		nd6_flush_holdchain(ifp, ln, chain);
+	if (flush_holdchain)
+		nd6_flush_children_holdchain(ifp, ln);
 
 	if (checklink)
 		pfxlist_onlink_check();