netinet6: simplify defrouter_select_fib()

[melifaro]

Summary

Simplify defrouter_select_fib():

• factor out underlying llenty check into a separate function and use it consistently
• join epoch once instead of multiple in/out jumps
• don't execute body when RT_ALL_FIBS supplied

sys/netinet6/nd6_rtr.c

default:
                  * Or, can we even panic?
                  */
                 log(LOG_ERR, "rtpref: impossible RA flag %x\n", dr->raflags);
                 return (RTPREF_INVALID);
         }
         /* NOTREACHED */
 }
 
+static bool
+is_dr_reachable(const struct nd_defrouter *dr) {
+        struct llentry *ln = NULL;
+
+        ln = nd6_lookup(&dr->rtaddr, LLE_SF(AF_INET6, 0), dr->ifp);
+        if (ln == NULL)
+                return (false);
+        bool reachable = ND6_IS_LLINFO_PROBREACH(ln);
+        LLE_RUNLOCK(ln);
+        return reachable;
+}
+
 /*
  * Default Router Selection according to Section 6.3.6 of RFC 2461 and
  * draft-ietf-ipngwg-router-selection:
  * 1) Routers that are reachable or probably reachable should be preferred.
  *    If we have more than one (probably) reachable router, prefer ones
  *    with the highest router preference.
  * 2) When no routers on the list are known to be reachable or
  *    probably reachable, routers SHOULD be selected in a round-robin

  * at a time based on the receiving interface's FIB. If @fibnum is RT_ALL_FIBS,
  * we do the whole thing multiple times.
  */
 void
 defrouter_select_fib(int fibnum)
 {
         struct epoch_tracker et;
         struct nd_defrouter *dr, *selected_dr, *installed_dr;
-        struct llentry *ln = NULL;
 
         if (fibnum == RT_ALL_FIBS) {
                 for (fibnum = 0; fibnum < rt_numfibs; fibnum++) {
                         defrouter_select_fib(fibnum);
                 }
+                return;
         }
 
         ND6_RLOCK();
         /*
          * Let's handle easy case (3) first:
          * If default router list is empty, there's nothing to be done.
          */
         if (TAILQ_EMPTY(&V_nd6_defrouter)) {
                 ND6_RUNLOCK();
                 return;
         }
 
         /*
          * Search for a (probably) reachable router from the list.
          * We just pick up the first reachable one (if any), assuming that
          * the ordering rule of the list described in defrtrlist_update().
          */
         selected_dr = installed_dr = NULL;
-        TAILQ_FOREACH(dr, &V_nd6_defrouter, dr_entry) {
-                NET_EPOCH_ENTER(et);
-                if (selected_dr == NULL && dr->ifp->if_fib == fibnum &&
-                    (ln = nd6_lookup(&dr->rtaddr, LLE_SF(AF_INET6, 0), dr->ifp)) &&
-                    ND6_IS_LLINFO_PROBREACH(ln)) {
+        TAILQ_FOREACH(dr, &V_nd6_defrouter, dr_entry) {
+                if (dr->ifp->if_fib != fibnum)
+                        continue;
+
+                if (selected_dr == NULL && is_dr_reachable(dr)) {
                         selected_dr = dr;
                         defrouter_ref(selected_dr);
                 }
-                NET_EPOCH_EXIT(et);
-                if (ln != NULL) {
-                        LLE_RUNLOCK(ln);
-                        ln = NULL;
-                }
 
-                if (dr->installed && dr->ifp->if_fib == fibnum) {
+                if (dr->installed) {
                         if (installed_dr == NULL) {
                                 installed_dr = dr;
                                 defrouter_ref(installed_dr);
                         } else {
                                 /*
                                  * this should not happen.
                                  * warn for diagnosis.
                                  */
                                 log(LOG_ERR, "defrouter_select_fib: more than "
                                              "one router is installed\n");
                         }
                 }
         }
+
         /*
          * If none of the default routers was found to be reachable,
          * round-robin the list regardless of preference.
          * Otherwise, if we have an installed router, check if the selected
          * (reachable) router should really be preferred to the installed one.
          * We only prefer the new router when the old one is not reachable
          * or when the new one has a really higher preference value.
          */
         if (selected_dr == NULL) {
                 if (installed_dr == NULL ||
                     TAILQ_NEXT(installed_dr, dr_entry) == NULL)
                         dr = TAILQ_FIRST(&V_nd6_defrouter);
                 else
                         dr = TAILQ_NEXT(installed_dr, dr_entry);
 
                 /* Ensure we select a router for this FIB. */
                 TAILQ_FOREACH_FROM(dr, &V_nd6_defrouter, dr_entry) {
                         if (dr->ifp->if_fib == fibnum) {
                                 selected_dr = dr;
                                 defrouter_ref(selected_dr);
                                 break;
                         }
                 }
         } else if (installed_dr != NULL) {
-                NET_EPOCH_ENTER(et);
-                if ((ln = nd6_lookup(&installed_dr->rtaddr, 0,
-                                     installed_dr->ifp)) &&
-                    ND6_IS_LLINFO_PROBREACH(ln) &&
-                    installed_dr->ifp->if_fib == fibnum &&
+                if (is_dr_reachable(installed_dr) &&
                     rtpref(selected_dr) <= rtpref(installed_dr)) {
                         defrouter_rele(selected_dr);
                         selected_dr = installed_dr;
                 }
-                NET_EPOCH_EXIT(et);
-                if (ln != NULL)
-                        LLE_RUNLOCK(ln);
         }
         ND6_RUNLOCK();
 
-        NET_EPOCH_ENTER(et);
         /*
          * If we selected a router for this FIB and it's different
          * than the installed one, remove the installed router and
          * install the selected one in its place.
          */
         if (installed_dr != selected_dr) {
                 if (installed_dr != NULL) {
                         defrouter_delreq(installed_dr);

  * detect if a given prefix has a (probably) reachable advertising router.
  * XXX: lengthy function name...
  */
 static struct nd_pfxrouter *
 find_pfxlist_reachable_router(struct nd_prefix *pr)
 {
         struct epoch_tracker et;
         struct nd_pfxrouter *pfxrtr;
-        struct llentry *ln;
-        int canreach;
 
         ND6_LOCK_ASSERT();
 
         NET_EPOCH_ENTER(et);
         LIST_FOREACH(pfxrtr, &pr->ndpr_advrtrs, pfr_entry) {
-                ln = nd6_lookup(&pfxrtr->router->rtaddr, LLE_SF(AF_INET6, 0),
-                    pfxrtr->router->ifp);
-                if (ln == NULL)
-                        continue;
-                canreach = ND6_IS_LLINFO_PROBREACH(ln);
-                LLE_RUNLOCK(ln);
-                if (canreach)
+                if (is_dr_reachable(pfxrtr->router))
                         break;
         }
         NET_EPOCH_EXIT(et);
         return (pfxrtr);
 }
 
 /*
  * Check if each prefix in the prefix list has at least one available router