commit 2a51860533e251991aeaf77713c0bd284da83fe8
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Fri May 13 10:41:50 2016 +0900

    Add if_get, if_get_byindex and if_put

diff --git a/sys/net/if.c b/sys/net/if.c
index 7f48bdb..2a72c39 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -2119,12 +2119,92 @@ out:
 	return ifp;
 }
 
+/*
+ * Get a reference of an ifnet object by an interface name.
+ * The returned reference is protected by psref(9). The caller
+ * must release a returned reference by if_put after use.
+ */
+struct ifnet *
+if_get(const char *name, struct psref *psref)
+{
+	struct ifnet *ifp;
+	const char *cp = name;
+	u_int unit = 0;
+	u_int i;
+	int s;
+
+	/*
+	 * If the entire name is a number, treat it as an ifindex.
+	 */
+	for (i = 0; i < IFNAMSIZ && *cp >= '0' && *cp <= '9'; i++, cp++) {
+		unit = unit * 10 + (*cp - '0');
+	}
+
+	/*
+	 * If the number took all of the name, then it's a valid ifindex.
+	 */
+	if (i == IFNAMSIZ || (cp != name && *cp == '\0')) {
+		if (unit >= if_indexlim)
+			return NULL;
+		ifp = ifindex2ifnet[unit];
+		if (ifp == NULL || ifp->if_output == if_nulloutput)
+			return NULL;
+		return ifp;
+	}
+
+	ifp = NULL;
+	s = pserialize_read_enter();
+	IFNET_READER_FOREACH(ifp) {
+		if (ifp->if_output == if_nulloutput)
+			continue;
+		if (strcmp(ifp->if_xname, name) == 0) {
+			psref_acquire(psref, &ifp->if_psref,
+			    ifnet_psref_class);
+			goto out;
+		}
+	}
+out:
+	pserialize_read_exit(s);
+	return ifp;
+}
+
+/*
+ * Release a reference of an ifnet object given by if_get or
+ * if_get_byindex.
+ */
+void
+if_put(const struct ifnet *ifp, struct psref *psref)
+{
+
+	psref_release(psref, &ifp->if_psref, ifnet_psref_class);
+}
+
 ifnet_t *
 if_byindex(u_int idx)
 {
 	return (idx < if_indexlim) ? ifindex2ifnet[idx] : NULL;
 }
 
+/*
+ * Get a reference of an ifnet object by an interface index.
+ * The returned reference is protected by psref(9). The caller
+ * must release a returned reference by if_put after use.
+ */
+ifnet_t *
+if_get_byindex(u_int idx, struct psref *psref)
+{
+	ifnet_t *ifp;
+	int s;
+
+	s = pserialize_read_enter();
+	ifp = (idx < if_indexlim) ? ifindex2ifnet[idx] : NULL;
+	if (ifp != NULL)
+		psref_acquire(psref, &ifp->if_psref, ifnet_psref_class);
+	pserialize_read_exit(s);
+
+	return ifp;
+}
+
 /* common */
 int
 ifioctl_common(struct ifnet *ifp, u_long cmd, void *data)
diff --git a/sys/net/if.h b/sys/net/if.h
index e2d0f87..69e55c9 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -912,6 +912,10 @@ extern int (*ifioctl)(struct socket *, u_long, void *, struct lwp *);
 int	ifioctl_common(struct ifnet *, u_long, void *);
 int	ifpromisc(struct ifnet *, int);
 struct	ifnet *ifunit(const char *);
+struct	ifnet *if_get(const char *, struct psref *);
+ifnet_t *if_byindex(u_int);
+ifnet_t *if_get_byindex(u_int, struct psref *);
+void	if_put(const struct ifnet *, struct psref *);
 int	if_addr_init(ifnet_t *, struct ifaddr *, bool);
 int	if_do_dad(struct ifnet *);
 int	if_mcast_op(ifnet_t *, const unsigned long, const struct sockaddr *);
@@ -1047,8 +1051,6 @@ extern kmutex_t ifnet_mtx;
 
 extern struct ifnet *lo0ifp;
 
-ifnet_t *	if_byindex(u_int);
-
 /*
  * ifq sysctl support
  */