Add rib_walk_from() wrapper for selective rib tree traversal.

Provide wrapper for the rnh_walktree_from() rib callback.
As currently `struct rib_head` is considered internal to the
 routing subsystem, this wrapper is necessary to maintain isolation
 from the external code.

Differential Revision: https://reviews.freebsd.org/D29971
MFC after:	1 week

2 files changed, 38 insertions, 0 deletions

diff --git a/sys/net/route/route_ctl.h b/sys/net/route/route_ctl.h
index 46dba759f8df..4fe45cc8a970 100644
--- a/sys/net/route/route_ctl.h
+++ b/sys/net/route/route_ctl.h
@@ -62,6 +62,10 @@ int rib_add_redirect(u_int fibnum, struct sockaddr *dst,
   struct sockaddr *gateway, struct sockaddr *author, struct ifnet *ifp,
   int flags, int expire_sec);
 
+/* common flags for the functions below */
+#define	RIB_FLAG_WLOCK		0x01	/* Need exclusive rnh lock */
+#define	RIB_FLAG_LOCKED		0x02	/* Do not explicitly acquire rnh lock */
+
 enum rib_walk_hook {
 	RIB_WALK_HOOK_PRE,	/* Hook is called before iteration */
 	RIB_WALK_HOOK_POST,	/* Hook is called after iteration */
@@ -77,6 +81,8 @@ void rib_walk_ext_internal(struct rib_head *rnh, bool wlock,
     rib_walktree_f_t *wa_f, rib_walk_hook_f_t *hook_f, void *arg);
 void rib_walk_ext_locked(struct rib_head *rnh, rib_walktree_f_t *wa_f,
     rib_walk_hook_f_t *hook_f, void *arg);
+void rib_walk_from(uint32_t fibnum, int family, uint32_t flags, struct sockaddr *prefix,
+    struct sockaddr *mask, rib_walktree_f_t *wa_f, void *arg);
 
 void rib_walk_del(u_int fibnum, int family, rib_filter_f_t *filter_f,
     void *arg, bool report);
diff --git a/sys/net/route/route_helpers.c b/sys/net/route/route_helpers.c
index 782e160ca51b..5d29197cc4fb 100644
--- a/sys/net/route/route_helpers.c
+++ b/sys/net/route/route_helpers.c
@@ -129,6 +129,38 @@ rib_walk(uint32_t fibnum, int family, bool wlock, rib_walktree_f_t *wa_f,
 }
 
 /*
+ * Calls @wa_f with @arg for each entry in the table matching @prefix/@mask.
+ *
+ * The following flags are supported:
+ *  RIB_FLAG_WLOCK: acquire exclusive lock
+ *  RIB_FLAG_LOCKED: Assumes the table is already locked & skip locking
+ *
+ * By default, table is traversed under read lock.
+ */
+void
+rib_walk_from(uint32_t fibnum, int family, uint32_t flags, struct sockaddr *prefix,
+    struct sockaddr *mask, rib_walktree_f_t *wa_f, void *arg)
+{
+	RIB_RLOCK_TRACKER;
+	struct rib_head *rnh = rt_tables_get_rnh(fibnum, family);
+
+	if (rnh == NULL)
+		return;
+
+	if (flags & RIB_FLAG_WLOCK)
+		RIB_WLOCK(rnh);
+	else if (!(flags & RIB_FLAG_LOCKED))
+		RIB_RLOCK(rnh);
+
+	rnh->rnh_walktree_from(&rnh->head, prefix, mask, (walktree_f_t *)wa_f, arg);
+
+	if (flags & RIB_FLAG_WLOCK)
+		RIB_WUNLOCK(rnh);
+	else if (!(flags & RIB_FLAG_LOCKED))
+		RIB_RUNLOCK(rnh);
+}
+
+/*
  * Iterates over all existing fibs in system calling
  *  @hook_f function before/after traversing each fib.
  *  Calls @wa_f function for each element in current fib.