commit 7ac99af6c4007d1a35444dedeaa506b4b1be6def
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Tue Mar 22 19:40:00 2016 +0900

    Constify rtentry of if_output

diff --git a/sys/dev/ic/hd64570.c b/sys/dev/ic/hd64570.c
index 9e841fa..7ee290e 100644
--- a/sys/dev/ic/hd64570.c
+++ b/sys/dev/ic/hd64570.c
@@ -160,7 +160,7 @@ static	void sca_port_up(sca_port_t *);
 static	void sca_port_down(sca_port_t *);
 
 static	int sca_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-			    struct rtentry *);
+			    const struct rtentry *);
 static	int sca_ioctl(struct ifnet *, u_long, void *);
 static	void sca_start(struct ifnet *);
 static	void sca_watchdog(struct ifnet *);
@@ -792,7 +792,7 @@ sca_output(
     struct ifnet *ifp,
     struct mbuf *m,
     const struct sockaddr *dst,
-    struct rtentry *rt0)
+    const struct rtentry *rt0)
 {
 	struct hdlc_header *hdlc;
 	struct ifqueue *ifq = NULL;
diff --git a/sys/dev/pci/if_lmc.c b/sys/dev/pci/if_lmc.c
index 3ba7854..d0b306e 100644
--- a/sys/dev/pci/if_lmc.c
+++ b/sys/dev/pci/if_lmc.c
@@ -3355,7 +3355,7 @@ ifnet_input(struct ifnet *ifp, struct mbuf *mbuf)
  */
 static int  /* context: process */
 ifnet_output(struct ifnet *ifp, struct mbuf *m,
- const struct sockaddr *dst, struct rtentry *rt)
+ const struct sockaddr *dst, const struct rtentry *rt)
   {
   softc_t *sc = IFP2SC(ifp);
   int error = 0;
diff --git a/sys/dev/pci/if_lmc.h b/sys/dev/pci/if_lmc.h
index e99c155..8eea023 100644
--- a/sys/dev/pci/if_lmc.h
+++ b/sys/dev/pci/if_lmc.h
@@ -1311,7 +1311,7 @@ static int rawip_detach(softc_t *);
 #if IFNET
 static void ifnet_input(struct ifnet *, struct mbuf *);
 static int ifnet_output(struct ifnet *, struct mbuf *,
-			const struct sockaddr *, struct rtentry *);
+			const struct sockaddr *, const struct rtentry *);
 static int ifnet_ioctl(struct ifnet *, u_long, void *);
 static void ifnet_start(struct ifnet *);
 static void ifnet_watchdog(struct ifnet *);
diff --git a/sys/dev/usb/if_upl.c b/sys/dev/usb/if_upl.c
index 2b480ddd..e40957b 100644
--- a/sys/dev/usb/if_upl.c
+++ b/sys/dev/usb/if_upl.c
@@ -193,7 +193,7 @@ Static void upl_stop(struct upl_softc *);
 Static void upl_watchdog(struct ifnet *);
 
 Static int upl_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-		      struct rtentry *);
+		      const struct rtentry *);
 Static void upl_input(struct ifnet *, struct mbuf *);
 
 /*
@@ -985,7 +985,7 @@ upl_stop(struct upl_softc *sc)
 
 Static int
 upl_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt0)
+    const struct rtentry *rt0)
 {
 	int s, len, error;
 
diff --git a/sys/dev/usb/uhso.c b/sys/dev/usb/uhso.c
index 300bd29..cb6b725 100644
--- a/sys/dev/usb/uhso.c
+++ b/sys/dev/usb/uhso.c
@@ -421,7 +421,8 @@ Static int  uhso_ifnet_ioctl(struct ifnet *, u_long, void *);
 Static int  uhso_ifnet_init(struct uhso_port *);
 Static void uhso_ifnet_clean(struct uhso_port *);
 Static void uhso_ifnet_start(struct ifnet *);
-Static int  uhso_ifnet_output(struct ifnet *, struct mbuf *, const struct sockaddr *, struct rtentry *);
+Static int  uhso_ifnet_output(struct ifnet *, struct mbuf *,
+    const struct sockaddr *, const struct rtentry *);
 
 
 /*******************************************************************************
@@ -2339,7 +2340,7 @@ uhso_ifnet_start(struct ifnet *ifp)
 
 Static int
 uhso_ifnet_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt0)
+    const struct rtentry *rt0)
 {
 	int error;
 
diff --git a/sys/net/if.c b/sys/net/if.c
index 4f6beb5..341b6ee 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -308,7 +308,7 @@ if_initname(struct ifnet *ifp, const char *name, int unit)
 
 int
 if_nulloutput(struct ifnet *ifp, struct mbuf *m,
-    const struct sockaddr *so, struct rtentry *rt)
+    const struct sockaddr *so, const struct rtentry *rt)
 {
 
 	return ENXIO;
diff --git a/sys/net/if.h b/sys/net/if.h
index 12c3d72..4c4ac70 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -267,7 +267,7 @@ typedef struct ifnet {
 	 */
 	int	(*if_output)		/* output routine (enqueue) */
 		    (struct ifnet *, struct mbuf *, const struct sockaddr *,
-		     struct rtentry *);
+		     const struct rtentry *);
 	void	(*_if_input)		/* input routine (from h/w driver) */
 		    (struct ifnet *, struct mbuf *);
 	void	(*if_start)		/* initiate output routine */
@@ -945,7 +945,7 @@ int	ifq_enqueue2(struct ifnet *, struct ifqueue *, struct mbuf *);
 int	loioctl(struct ifnet *, u_long, void *);
 void	loopattach(int);
 int	looutput(struct ifnet *,
-	   struct mbuf *, const struct sockaddr *, struct rtentry *);
+	   struct mbuf *, const struct sockaddr *, const struct rtentry *);
 void	lortrequest(int, struct rtentry *, const struct rt_addrinfo *);
 
 /*
@@ -953,7 +953,7 @@ void	lortrequest(int, struct rtentry *, const struct rt_addrinfo *);
  * an interface is going away without having to burn a flag.
  */
 int	if_nulloutput(struct ifnet *, struct mbuf *,
-	    const struct sockaddr *, struct rtentry *);
+	    const struct sockaddr *, const struct rtentry *);
 void	if_nullinput(struct ifnet *, struct mbuf *);
 void	if_nullstart(struct ifnet *);
 int	if_nullioctl(struct ifnet *, u_long, void *);
diff --git a/sys/net/if_atm.h b/sys/net/if_atm.h
index 4677a57..e59f506 100644
--- a/sys/net/if_atm.h
+++ b/sys/net/if_atm.h
@@ -136,7 +136,7 @@ void	atm_ifattach(struct ifnet *);
 void	atm_input(struct ifnet *, struct atm_pseudohdr *,
 		struct mbuf *, void *);
 int	atm_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-		struct rtentry *);
+		const struct rtentry *);
 #endif
 #ifdef ATM_PVCEXT
 #ifdef _KERNEL
diff --git a/sys/net/if_atmsubr.c b/sys/net/if_atmsubr.c
index ce69db3..06c835d 100644
--- a/sys/net/if_atmsubr.c
+++ b/sys/net/if_atmsubr.c
@@ -90,7 +90,7 @@ __KERNEL_RCSID(0, "$NetBSD: if_atmsubr.c,v 1.57 2016/04/20 09:01:04 knakahara Ex
 
 int
 atm_output(struct ifnet *ifp, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	uint16_t etype = 0;			/* if using LLC/SNAP */
 	int error = 0, sz;
diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index 153348f..3334675 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -1415,7 +1415,7 @@ bridge_enqueue(struct bridge_softc *sc, struct ifnet *dst_ifp, struct mbuf *m,
  */
 int
 bridge_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *sa,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	struct ether_header *eh;
 	struct ifnet *dst_if;
diff --git a/sys/net/if_bridgevar.h b/sys/net/if_bridgevar.h
index 66be142..218d5af 100644
--- a/sys/net/if_bridgevar.h
+++ b/sys/net/if_bridgevar.h
@@ -334,7 +334,7 @@ extern const uint8_t bstp_etheraddr[];
 void	bridge_ifdetach(struct ifnet *);
 
 int	bridge_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-	    struct rtentry *);
+	    const struct rtentry *);
 
 void	bstp_initialization(struct bridge_softc *);
 void	bstp_stop(struct bridge_softc *);
diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index 050e311..fa8d3e1 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -178,7 +178,7 @@ const uint8_t ethermulticastaddr_slowprotocols[ETHER_ADDR_LEN] =
 #define senderr(e) { error = (e); goto bad;}
 
 static	int ether_output(struct ifnet *, struct mbuf *,
-	    const struct sockaddr *, struct rtentry *);
+	    const struct sockaddr *, const struct rtentry *);
 
 /*
  * Ethernet output routine.
@@ -188,7 +188,7 @@ static	int ether_output(struct ifnet *, struct mbuf *,
 static int
 ether_output(struct ifnet * const ifp0, struct mbuf * const m0,
 	const struct sockaddr * const dst,
-	struct rtentry *rt)
+	const struct rtentry *rt)
 {
 	uint16_t etype = 0;
 	int error = 0, hdrcmplt = 0;
diff --git a/sys/net/if_faith.c b/sys/net/if_faith.c
index eefe7a5..ac58887 100644
--- a/sys/net/if_faith.c
+++ b/sys/net/if_faith.c
@@ -86,7 +86,7 @@ __KERNEL_RCSID(0, "$NetBSD: if_faith.c,v 1.51 2015/08/20 14:40:19 christos Exp $
 
 static int	faithioctl(struct ifnet *, u_long, void *);
 static int	faithoutput(struct ifnet *, struct mbuf *,
-		            const struct sockaddr *, struct rtentry *);
+		            const struct sockaddr *, const struct rtentry *);
 static void	faithrtrequest(int, struct rtentry *,
 		               const struct rt_addrinfo *);
 
@@ -143,7 +143,7 @@ faith_clone_destroy(struct ifnet *ifp)
 
 static int
 faithoutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	pktqueue_t *pktq;
 	size_t pktlen;
diff --git a/sys/net/if_fddisubr.c b/sys/net/if_fddisubr.c
index 2386401..df9c5bb 100644
--- a/sys/net/if_fddisubr.c
+++ b/sys/net/if_fddisubr.c
@@ -176,7 +176,7 @@ extern u_char	aarp_org_code[ 3 ];
 #define	CFDDIADDR(ifp)		CLLADDR((ifp)->if_sadl)
 
 static	int fddi_output(struct ifnet *, struct mbuf *,
-	    const struct sockaddr *, struct rtentry *);
+	    const struct sockaddr *, const struct rtentry *);
 static	void fddi_input(struct ifnet *, struct mbuf *);
 
 /*
@@ -186,7 +186,7 @@ static	void fddi_input(struct ifnet *, struct mbuf *);
  */
 static int
 fddi_output(struct ifnet *ifp0, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	uint16_t etype;
 	int error = 0, hdrcmplt = 0;
diff --git a/sys/net/if_gif.c b/sys/net/if_gif.c
index 3fceeb3..0c87983 100644
--- a/sys/net/if_gif.c
+++ b/sys/net/if_gif.c
@@ -306,7 +306,7 @@ gif_check_nesting(struct ifnet *ifp, struct mbuf *m)
 
 int
 gif_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	struct gif_softc *sc = ifp->if_softc;
 	int error = 0;
diff --git a/sys/net/if_gif.h b/sys/net/if_gif.h
index 1d66b1d..65ebb62 100644
--- a/sys/net/if_gif.h
+++ b/sys/net/if_gif.h
@@ -73,7 +73,7 @@ struct gif_softc {
 void	gifattach0(struct gif_softc *);
 void	gif_input(struct mbuf *, int, struct ifnet *);
 int	gif_output(struct ifnet *, struct mbuf *,
-		   const struct sockaddr *, struct rtentry *);
+		   const struct sockaddr *, const struct rtentry *);
 int	gif_ioctl(struct ifnet *, u_long, void *);
 int	gif_set_tunnel(struct ifnet *, struct sockaddr *, struct sockaddr *);
 void	gif_delete_tunnel(struct ifnet *);
diff --git a/sys/net/if_gre.c b/sys/net/if_gre.c
index d08a4d1..20639ee 100644
--- a/sys/net/if_gre.c
+++ b/sys/net/if_gre.c
@@ -152,7 +152,7 @@ static int gre_input(struct gre_softc *, struct mbuf *, int,
     const struct gre_h *);
 static bool gre_is_nullconf(const struct gre_soparm *);
 static int gre_output(struct ifnet *, struct mbuf *,
-			   const struct sockaddr *, struct rtentry *);
+			   const struct sockaddr *, const struct rtentry *);
 static int gre_ioctl(struct ifnet *, u_long, void *);
 static int gre_getsockname(struct socket *, struct sockaddr *);
 static int gre_getpeername(struct socket *, struct sockaddr *);
@@ -878,7 +878,7 @@ gre_input(struct gre_softc *sc, struct mbuf *m, int hlen,
  */
 static int
 gre_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-	   struct rtentry *rt)
+	   const struct rtentry *rt)
 {
 	int error = 0;
 	struct gre_softc *sc = ifp->if_softc;
diff --git a/sys/net/if_hippisubr.c b/sys/net/if_hippisubr.c
index 698a2e7..453bd02 100644
--- a/sys/net/if_hippisubr.c
+++ b/sys/net/if_hippisubr.c
@@ -73,7 +73,7 @@ __KERNEL_RCSID(0, "$NetBSD: if_hippisubr.c,v 1.46 2016/04/20 09:01:04 knakahara
 #endif
 
 static int	hippi_output(struct ifnet *, struct mbuf *,
-			     const struct sockaddr *, struct rtentry *);
+			     const struct sockaddr *, const struct rtentry *);
 static void	hippi_input(struct ifnet *, struct mbuf *);
 
 /*
@@ -85,7 +85,7 @@ static void	hippi_input(struct ifnet *, struct mbuf *);
 
 static int
 hippi_output(struct ifnet *ifp, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	uint16_t htype;
 	uint32_t ifield = 0;
diff --git a/sys/net/if_ieee1394subr.c b/sys/net/if_ieee1394subr.c
index b3402b9..754e349 100644
--- a/sys/net/if_ieee1394subr.c
+++ b/sys/net/if_ieee1394subr.c
@@ -79,12 +79,12 @@ __KERNEL_RCSID(0, "$NetBSD: if_ieee1394subr.c,v 1.53 2016/04/20 09:01:04 knakaha
 #define	senderr(e)	do { error = (e); goto bad; } while(0/*CONSTCOND*/)
 
 static int  ieee1394_output(struct ifnet *, struct mbuf *,
-		const struct sockaddr *, struct rtentry *);
+		const struct sockaddr *, const struct rtentry *);
 static struct mbuf *ieee1394_reass(struct ifnet *, struct mbuf *, uint16_t);
 
 static int
 ieee1394_output(struct ifnet *ifp, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	uint16_t etype = 0;
 	struct mbuf *m;
diff --git a/sys/net/if_loop.c b/sys/net/if_loop.c
index 5c6e893..4163d1f 100644
--- a/sys/net/if_loop.c
+++ b/sys/net/if_loop.c
@@ -205,7 +205,7 @@ loop_clone_destroy(struct ifnet *ifp)
 
 int
 looutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	pktqueue_t *pktq = NULL;
 	struct ifqueue *ifq = NULL;
diff --git a/sys/net/if_mpls.c b/sys/net/if_mpls.c
index 6434dd6..da27fd5 100644
--- a/sys/net/if_mpls.c
+++ b/sys/net/if_mpls.c
@@ -89,9 +89,10 @@ static struct if_clone mpls_if_cloner =
 
 static void mpls_input(struct ifnet *, struct mbuf *);
 static int mpls_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-	struct rtentry *);
+	const struct rtentry *);
 static int mpls_ioctl(struct ifnet *, u_long, void *);
-static int mpls_send_frame(struct mbuf *, struct ifnet *, struct rtentry *);
+static int mpls_send_frame(struct mbuf *, struct ifnet *,
+    const struct rtentry *);
 static int mpls_lse(struct mbuf *);
 
 #ifdef INET
@@ -201,7 +202,8 @@ mplsintr(void)
  * prepend shim and deliver
  */
 static int
-mpls_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst, struct rtentry *rt)
+mpls_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
+    const struct rtentry *rt)
 {
 	union mpls_shim mh, *pms;
 	struct rtentry *rt1;
@@ -438,6 +440,12 @@ mpls_lse(struct mbuf *m)
 			return ENOBUFS;
 	}
 
+	if ((rt->rt_flags & RTF_GATEWAY) == 0) {
+		error = EHOSTUNREACH;
+		goto done;
+	}
+
+	rt->rt_use++;
 	error = mpls_send_frame(m, rt->rt_ifp, rt);
 
 done:
@@ -450,16 +458,11 @@ done:
 }
 
 static int
-mpls_send_frame(struct mbuf *m, struct ifnet *ifp, struct rtentry *rt)
+mpls_send_frame(struct mbuf *m, struct ifnet *ifp, const struct rtentry *rt)
 {
 	union mpls_shim msh;
 	int ret;
 
-	if ((rt->rt_flags & RTF_GATEWAY) == 0)
-		return EHOSTUNREACH;
-
-	rt->rt_use++;
-
 	msh.s_addr = MPLS_GETSADDR(rt);
 	if (msh.shim.label == MPLS_LABEL_IMPLNULL ||
 	    (m->m_flags & (M_MCAST | M_BCAST))) {
diff --git a/sys/net/if_ppp.c b/sys/net/if_ppp.c
index a740b98..efce287 100644
--- a/sys/net/if_ppp.c
+++ b/sys/net/if_ppp.c
@@ -839,7 +839,7 @@ pppsioctl(struct ifnet *ifp, u_long cmd, void *data)
  */
 int
 pppoutput(struct ifnet *ifp, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rtp)
+    const struct rtentry *rtp)
 {
 	struct ppp_softc *sc = ifp->if_softc;
 	int protocol, address, control;
diff --git a/sys/net/if_pppvar.h b/sys/net/if_pppvar.h
index 0bb9a29..e9b1dcb 100644
--- a/sys/net/if_pppvar.h
+++ b/sys/net/if_pppvar.h
@@ -159,7 +159,7 @@ void	ppp_restart(struct ppp_softc *);
 void	ppppktin(struct ppp_softc *, struct mbuf *, int);
 struct	mbuf *ppp_dequeue(struct ppp_softc *);
 int	pppoutput(struct ifnet *, struct mbuf *, const struct sockaddr *,
-	    struct rtentry *);
+	    const struct rtentry *);
 #endif /* _KERNEL */
 
 #endif /* !_NET_IF_PPPVAR_H_ */
diff --git a/sys/net/if_sl.c b/sys/net/if_sl.c
index c7f3c63..b6bba13 100644
--- a/sys/net/if_sl.c
+++ b/sys/net/if_sl.c
@@ -198,7 +198,7 @@ static int	slinput(int, struct tty *);
 static int	slioctl(struct ifnet *, u_long, void *);
 static int	slopen(dev_t, struct tty *);
 static int	sloutput(struct ifnet *, struct mbuf *, const struct sockaddr *,
-			 struct rtentry *);
+			 const struct rtentry *);
 static int	slstart(struct tty *);
 static int	sltioctl(struct tty *, u_long, void *, int, struct lwp *);
 
@@ -433,7 +433,7 @@ sltioctl(struct tty *tp, u_long cmd, void *data, int flag,
  */
 static int
 sloutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rtp)
+    const struct rtentry *rtp)
 {
 	struct sl_softc *sc = ifp->if_softc;
 	struct ip *ip;
diff --git a/sys/net/if_spppsubr.c b/sys/net/if_spppsubr.c
index 1f02549..80a67f3 100644
--- a/sys/net/if_spppsubr.c
+++ b/sys/net/if_spppsubr.c
@@ -258,7 +258,7 @@ static u_short interactive_ports[8] = {
 	int debug = ifp->if_flags & IFF_DEBUG
 
 static int sppp_output(struct ifnet *ifp, struct mbuf *m,
-		       const struct sockaddr *dst, struct rtentry *rt);
+		       const struct sockaddr *dst, const struct rtentry *rt);
 
 static void sppp_cisco_send(struct sppp *sp, int type, int32_t par1, int32_t par2);
 static void sppp_cisco_input(struct sppp *sp, struct mbuf *m);
@@ -640,7 +640,7 @@ queue_pkt:
  */
 static int
 sppp_output(struct ifnet *ifp, struct mbuf *m,
-    const struct sockaddr *dst, struct rtentry *rt)
+    const struct sockaddr *dst, const struct rtentry *rt)
 {
 	struct sppp *sp = (struct sppp *) ifp;
 	struct ppp_header *h = NULL;
diff --git a/sys/net/if_srt.c b/sys/net/if_srt.c
index fe000fd..1ab780d 100644
--- a/sys/net/if_srt.c
+++ b/sys/net/if_srt.c
@@ -181,7 +181,7 @@ srt_if_output(
 	struct ifnet *ifp,
 	struct mbuf *m,
 	const struct sockaddr *to,
-	struct rtentry *rtp)
+	const struct rtentry *rtp)
 {
 	struct srt_softc *sc;
 	struct srt_rt *r;
diff --git a/sys/net/if_stf.c b/sys/net/if_stf.c
index 3ac7dd1..96d3ae6 100644
--- a/sys/net/if_stf.c
+++ b/sys/net/if_stf.c
@@ -168,7 +168,7 @@ static const struct encapsw in_stf_encapsw =
 static int stf_encapcheck(struct mbuf *, int, int, void *);
 static struct in6_ifaddr *stf_getsrcifa6(struct ifnet *);
 static int stf_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
-	struct rtentry *);
+	const struct rtentry *);
 static int isrfc1918addr(const struct in_addr *);
 static int stf_checkaddr4(struct stf_softc *, const struct in_addr *,
 	struct ifnet *);
@@ -325,7 +325,7 @@ stf_getsrcifa6(struct ifnet *ifp)
 
 static int
 stf_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt0)
+    const struct rtentry *rt0)
 {
 	struct rtentry *rt;
 	struct stf_softc *sc;
diff --git a/sys/net/if_strip.c b/sys/net/if_strip.c
index b26d8b2..14a7a20 100644
--- a/sys/net/if_strip.c
+++ b/sys/net/if_strip.c
@@ -332,7 +332,8 @@ static int	stripinput(int, struct tty *);
 static int	stripioctl(struct ifnet *, u_long, void *);
 static int	stripopen(dev_t, struct tty *);
 static int	stripoutput(struct ifnet *,
-		    struct mbuf *, const struct sockaddr *, struct rtentry *);
+		    struct mbuf *, const struct sockaddr *,
+		    const struct rtentry *);
 static int	stripstart(struct tty *);
 static int	striptioctl(struct tty *, u_long, void *, int, struct lwp *);
 
@@ -721,7 +722,7 @@ strip_send(struct strip_softc *sc, struct mbuf *m0)
  */
 int
 stripoutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	struct strip_softc *sc = ifp->if_softc;
 	struct ip *ip;
diff --git a/sys/net/if_tokensubr.c b/sys/net/if_tokensubr.c
index 405800b..e3e2af5 100644
--- a/sys/net/if_tokensubr.c
+++ b/sys/net/if_tokensubr.c
@@ -143,7 +143,7 @@ __KERNEL_RCSID(0, "$NetBSD: if_tokensubr.c,v 1.75 2016/04/20 09:01:04 knakahara
 #define RCF_SINGLEROUTE (2 << 8) | TOKEN_RCF_FRAME2 | TOKEN_RCF_BROADCAST_SINGLE
 
 static int	token_output(struct ifnet *, struct mbuf *,
-			     const struct sockaddr *, struct rtentry *);
+			     const struct sockaddr *, const struct rtentry *);
 static void	token_input(struct ifnet *, struct mbuf *);
 
 /*
@@ -154,7 +154,7 @@ static void	token_input(struct ifnet *, struct mbuf *);
  */
 static int
 token_output(struct ifnet *ifp0, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	uint16_t etype;
 	int error = 0;
diff --git a/sys/net/if_tun.c b/sys/net/if_tun.c
index 76c98ea..07b1459 100644
--- a/sys/net/if_tun.c
+++ b/sys/net/if_tun.c
@@ -73,7 +73,7 @@ static kmutex_t tun_softc_lock;
 
 static int	tun_ioctl(struct ifnet *, u_long, void *);
 static int	tun_output(struct ifnet *, struct mbuf *,
-			const struct sockaddr *, struct rtentry *rt);
+			const struct sockaddr *, const struct rtentry *rt);
 static int	tun_clone_create(struct if_clone *, int);
 static int	tun_clone_destroy(struct ifnet *);
 
@@ -494,7 +494,7 @@ tun_ioctl(struct ifnet *ifp, u_long cmd, void *data)
  */
 static int
 tun_output(struct ifnet *ifp, struct mbuf *m0, const struct sockaddr *dst,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	struct tun_softc *tp = ifp->if_softc;
 	int		s;
diff --git a/sys/net/route.c b/sys/net/route.c
index 0ca954c..c2d5e69 100644
--- a/sys/net/route.c
+++ b/sys/net/route.c
@@ -1488,13 +1488,13 @@ rt_settag(struct rtentry *rt, const struct sockaddr *tag)
 }
 
 struct sockaddr *
-rt_gettag(struct rtentry *rt)
+rt_gettag(const struct rtentry *rt)
 {
 	return rt->rt_tag;
 }
 
 int
-rt_check_reject_route(struct rtentry *rt, struct ifnet *ifp)
+rt_check_reject_route(const struct rtentry *rt, const struct ifnet *ifp)
 {
 
 	if ((rt->rt_flags & RTF_REJECT) != 0) {
diff --git a/sys/net/route.h b/sys/net/route.h
index ebef437..3cda045 100644
--- a/sys/net/route.h
+++ b/sys/net/route.h
@@ -403,9 +403,9 @@ int	rt_setgate(struct rtentry *, const struct sockaddr *);
 const struct sockaddr *
 	rt_settag(struct rtentry *, const struct sockaddr *);
 struct sockaddr *
-	rt_gettag(struct rtentry *);
+	rt_gettag(const struct rtentry *);
 
-int	rt_check_reject_route(struct rtentry *, struct ifnet *);
+int	rt_check_reject_route(const struct rtentry *, const struct ifnet *);
 
 static inline void
 rt_assert_referenced(const struct rtentry *rt)
diff --git a/sys/netinet/if_atm.c b/sys/netinet/if_atm.c
index 802c37d..9b44cd74 100644
--- a/sys/netinet/if_atm.c
+++ b/sys/netinet/if_atm.c
@@ -201,18 +201,18 @@ failed:
  */
 
 int
-atmresolve(struct rtentry *rt0, struct mbuf *m, const struct sockaddr *dst,
+atmresolve(const struct rtentry *rt0, struct mbuf *m, const struct sockaddr *dst,
     struct atm_pseudohdr *desten /* OUT */)
 {
 	const struct sockaddr_dl *sdl;
-	struct rtentry *rt = rt0;
+	struct rtentry *rt = NULL;
 
 	if (m->m_flags & (M_BCAST|M_MCAST)) {
 		log(LOG_INFO, "atmresolve: BCAST/MCAST packet detected/dumped\n");
 		goto bad;
 	}
 
-	if (rt == NULL) {
+	if (rt0 == NULL) {
 		rt = RTALLOC1(dst, 0);
 		if (rt == NULL)
 			goto bad; /* failed */
@@ -231,7 +231,7 @@ atmresolve(struct rtentry *rt0, struct mbuf *m, const struct sockaddr *dst,
 	 * ATM ARP [c.f. if_ether.c]).
 	 */
 
-	sdl = satocsdl(rt->rt_gateway);
+	sdl = satocsdl((rt ? rt : rt0)->rt_gateway);
 
 	/*
 	 * Check the address family and length is valid, the address
@@ -240,12 +240,12 @@ atmresolve(struct rtentry *rt0, struct mbuf *m, const struct sockaddr *dst,
 
 	if (sdl->sdl_family == AF_LINK && sdl->sdl_alen == sizeof(*desten)) {
 		memcpy(desten, CLLADDR(sdl), sdl->sdl_alen);
-		if (rt != rt0)
+		if (rt != NULL)
 			rtfree(rt);
 		return (1);	/* ok, go for it! */
 	}
 
-	if (rt != rt0)
+	if (rt != NULL)
 		rtfree(rt);
 
 	/*
diff --git a/sys/netinet/if_atm.h b/sys/netinet/if_atm.h
index 1a748c9..bb4cee8 100644
--- a/sys/netinet/if_atm.h
+++ b/sys/netinet/if_atm.h
@@ -33,7 +33,7 @@
  */
 
 void atm_rtrequest(int, struct rtentry *, const struct rt_addrinfo *);
-int atmresolve(struct rtentry *, struct mbuf *, const struct sockaddr *,
+int atmresolve(const struct rtentry *, struct mbuf *, const struct sockaddr *,
 		struct atm_pseudohdr *);
 
 #endif /* !_NETINET_IF_ATM_H_ */
diff --git a/sys/netinet/ip_carp.c b/sys/netinet/ip_carp.c
index d9491e5..8c20b57 100644
--- a/sys/netinet/ip_carp.c
+++ b/sys/netinet/ip_carp.c
@@ -2090,7 +2090,7 @@ carp_start(struct ifnet *ifp)
 
 int
 carp_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *sa,
-    struct rtentry *rt)
+    const struct rtentry *rt)
 {
 	struct carp_softc *sc = ((struct carp_softc *)ifp->if_softc);
 	KASSERT(KERNEL_LOCKED_P());
diff --git a/sys/netinet/ip_carp.h b/sys/netinet/ip_carp.h
index 377b62f..83d7bf0 100644
--- a/sys/netinet/ip_carp.h
+++ b/sys/netinet/ip_carp.h
@@ -163,6 +163,6 @@ struct ifaddr	*carp_iamatch6(void *, struct in6_addr *);
 struct ifnet	*carp_ourether(void *, struct ether_header *, u_char, int);
 int		 carp_input(struct mbuf *, u_int8_t *, u_int8_t *, u_int16_t);
 int		 carp_output(struct ifnet *, struct mbuf *,
-		     const struct sockaddr *, struct rtentry *);
+		     const struct sockaddr *, const struct rtentry *);
 #endif /* _KERNEL */
 #endif /* _NETINET_IP_CARP_H_ */
diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
index 0d63e47..5c18e02 100644
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -158,7 +158,8 @@ extern pfil_head_t *inet_pfil_hook;			/* XXX */
 int	ip_do_loopback_cksum = 0;
 
 static int
-ip_mark_mpls(struct ifnet * const ifp, struct mbuf * const m, struct rtentry *rt)
+ip_mark_mpls(struct ifnet * const ifp, struct mbuf * const m,
+    const struct rtentry *rt)
 {
 	int error = 0;
 #ifdef MPLS
@@ -193,7 +194,7 @@ ip_mark_mpls(struct ifnet * const ifp, struct mbuf * const m, struct rtentry *rt
  */
 int
 ip_if_output(struct ifnet * const ifp, struct mbuf * const m,
-    const struct sockaddr * const dst, struct rtentry *rt)
+    const struct sockaddr * const dst, const struct rtentry *rt)
 {
 	int error = 0;
 
diff --git a/sys/netinet/ip_var.h b/sys/netinet/ip_var.h
index ff4b5a3..b40f3c2 100644
--- a/sys/netinet/ip_var.h
+++ b/sys/netinet/ip_var.h
@@ -239,7 +239,7 @@ int	ip_setmoptions(struct ip_moptions **, const struct sockopt *sopt);
 int	ip_getmoptions(struct ip_moptions *, struct sockopt *sopt);
 
 int	ip_if_output(struct ifnet * const, struct mbuf * const,
-	    const struct sockaddr * const, struct rtentry *);
+	    const struct sockaddr * const, const struct rtentry *);
 
 /* IP Flow interface. */
 void	ipflow_init(void);
diff --git a/sys/netisdn/i4b_ipr.c b/sys/netisdn/i4b_ipr.c
index fcc2e6f..115f2f8 100644
--- a/sys/netisdn/i4b_ipr.c
+++ b/sys/netisdn/i4b_ipr.c
@@ -257,7 +257,8 @@ static int iprwatchdog(int unit);
 static void iprwatchdog(struct ifnet *ifp);
 #endif
 static void ipr_tx_queue_empty(void *);
-static int iripoutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst, struct rtentry *rtp);
+static int iripoutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
+    const struct rtentry *rtp);
 static void iripclearqueues(struct ipr_softc *sc);
 static void ipr_set_linktab(void *softc, isdn_link_t *ilt);
 static void ipr_activity(void *softc, int rxtx);
@@ -415,7 +416,7 @@ iripattach(void)
  *---------------------------------------------------------------------------*/
 static int
 iripoutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
-	 struct rtentry *rtp)
+	 const struct rtentry *rtp)
 {
 	struct ipr_softc *sc;
 	int s, rv;