Index: sys/netinet/igmp.c
===================================================================
--- sys/netinet/igmp.c
+++ sys/netinet/igmp.c
@@ -1466,7 +1466,7 @@
 		minlen += IGMP_V3_QUERY_MINLEN;
 	else
 		minlen += IGMP_MINLEN;
-	if ((m->m_flags & M_EXT || m->m_len < minlen) &&
+	if ((!M_WRITABLE(m) || m->m_len < minlen) &&
 	    (m = m_pullup(m, minlen)) == 0) {
 		IGMPSTAT_INC(igps_rcv_tooshort);
 		return (IPPROTO_DONE);
@@ -1557,7 +1557,7 @@
 				 */
 				igmpv3len = iphlen + IGMP_V3_QUERY_MINLEN +
 				    srclen;
-				if ((m->m_flags & M_EXT ||
+				if ((!M_WRITABLE(m) ||
 				     m->m_len < igmpv3len) &&
 				    (m = m_pullup(m, igmpv3len)) == NULL) {
 					IGMPSTAT_INC(igps_rcv_tooshort);
Index: sys/netinet/ip_mroute.c
===================================================================
--- sys/netinet/ip_mroute.c
+++ sys/netinet/ip_mroute.c
@@ -121,7 +121,6 @@
 #endif
 
 #define		VIFI_INVALID	((vifi_t) -1)
-#define		M_HASCL(m)	((m)->m_flags & M_EXT)
 
 static VNET_DEFINE(uint32_t, last_tv_sec); /* last time we processed this */
 #define	V_last_tv_sec	VNET(last_tv_sec)
@@ -1304,7 +1303,7 @@
 	}
 
 	mb0 = m_copypacket(m, M_NOWAIT);
-	if (mb0 && (M_HASCL(mb0) || mb0->m_len < hlen))
+	if (mb0 && (!M_WRITABLE(mb0) || mb0->m_len < hlen))
 	    mb0 = m_pullup(mb0, hlen);
 	if (mb0 == NULL) {
 	    free(rte, M_MRTABLE);
@@ -1544,7 +1543,7 @@
 		int hlen = ip->ip_hl << 2;
 		struct mbuf *mm = m_copy(m, 0, hlen);
 
-		if (mm && (M_HASCL(mm) || mm->m_len < hlen))
+		if (mm && (!M_WRITABLE(mm) || mm->m_len < hlen))
 		    mm = m_pullup(mm, hlen);
 		if (mm == NULL)
 		    return ENOBUFS;
@@ -1665,7 +1664,7 @@
      * so that ip_output() only scribbles on the copy.
      */
     mb_copy = m_copypacket(m, M_NOWAIT);
-    if (mb_copy && (M_HASCL(mb_copy) || mb_copy->m_len < hlen))
+    if (mb_copy && (!M_WRITABLE(mb_copy) || mb_copy->m_len < hlen))
 	mb_copy = m_pullup(mb_copy, hlen);
     if (mb_copy == NULL)
 	return;
Index: sys/netinet/ip_output.c
===================================================================
--- sys/netinet/ip_output.c
+++ sys/netinet/ip_output.c
@@ -1353,7 +1353,7 @@
 	 * modify the pack in order to generate checksums.
 	 */
 	copym = m_dup(m, M_NOWAIT);
-	if (copym != NULL && (copym->m_flags & M_EXT || copym->m_len < hlen))
+	if (copym != NULL && (!M_WRITABLE(copym) || copym->m_len < hlen))
 		copym = m_pullup(copym, hlen);
 	if (copym != NULL) {
 		/* If needed, compute the checksum and mark it as valid. */
Index: sys/netinet6/icmp6.c
===================================================================
--- sys/netinet6/icmp6.c
+++ sys/netinet6/icmp6.c
@@ -581,7 +583,7 @@
 			/* Give up remote */
 			break;
 		}
-		if ((n->m_flags & M_EXT) != 0
+		if (!M_WRITABLE(n)
 		 || n->m_len < off + sizeof(struct icmp6_hdr)) {
 			struct mbuf *n0 = n;
 			int n0len;
Index: sys/netinet6/ip6_mroute.c
===================================================================
--- sys/netinet6/ip6_mroute.c
+++ sys/netinet6/ip6_mroute.c
@@ -126,9 +126,6 @@
 
 static MALLOC_DEFINE(M_MRTABLE6, "mf6c", "multicast forwarding cache entry");
 
-/* XXX: this is a very common idiom; move to <sys/mbuf.h> ? */
-#define M_HASCL(m) ((m)->m_flags & M_EXT)
-
 static int	ip6_mdq(struct mbuf *, struct ifnet *, struct mf6c *);
 static void	phyint_send(struct ip6_hdr *, struct mif6 *, struct mbuf *);
 static int	register_send(struct ip6_hdr *, struct mif6 *, struct mbuf *);
@@ -1128,7 +1125,7 @@
 	 * Pullup packet header if needed before storing it,
 	 * as other references may modify it in the meantime.
 	 */
-	if (mb0 && (M_HASCL(mb0) || mb0->m_len < sizeof(struct ip6_hdr)))
+	if (mb0 && (!M_WRITABLE(mb0) || mb0->m_len < sizeof(struct ip6_hdr)))
 		mb0 = m_pullup(mb0, sizeof(struct ip6_hdr));
 	if (mb0 == NULL) {
 		free(rte, M_MRTABLE6);
@@ -1397,7 +1394,7 @@
 
 				mm = m_copy(m, 0, sizeof(struct ip6_hdr));
 				if (mm &&
-				    (M_HASCL(mm) ||
+				    (!M_WRITABLE(mm) ||
 				     mm->m_len < sizeof(struct ip6_hdr)))
 					mm = m_pullup(mm, sizeof(struct ip6_hdr));
 				if (mm == NULL)
@@ -1527,7 +1524,7 @@
 	 */
 	mb_copy = m_copy(m, 0, M_COPYALL);
 	if (mb_copy &&
-	    (M_HASCL(mb_copy) || mb_copy->m_len < sizeof(struct ip6_hdr)))
+	    (!M_WRITABLE(mb_copy) || mb_copy->m_len < sizeof(struct ip6_hdr)))
 		mb_copy = m_pullup(mb_copy, sizeof(struct ip6_hdr));
 	if (mb_copy == NULL) {
 		return;
Index: sys/netinet6/ip6_output.c
===================================================================
--- sys/netinet6/ip6_output.c
+++ sys/netinet6/ip6_output.c
@@ -1183,7 +1183,7 @@
 	for (mlast = n; mlast->m_next; mlast = mlast->m_next)
 		;
 
-	if ((mlast->m_flags & M_EXT) == 0 &&
+	if (M_WRITABLE(mlast) &&
 	    M_TRAILINGSPACE(mlast) >= sizeof(struct ip6_frag)) {
 		/* use the trailing space of the last mbuf for the fragment hdr */
 		*frghdrp = (struct ip6_frag *)(mtod(mlast, caddr_t) +
@@ -2905,7 +2905,7 @@
 	 * is in an mbuf cluster, so that we can safely override the IPv6
 	 * header portion later.
 	 */
-	if ((copym->m_flags & M_EXT) != 0 ||
+	if (!M_WRITABLE(copym) ||
 	    copym->m_len < sizeof(struct ip6_hdr)) {
 		copym = m_pullup(copym, sizeof(struct ip6_hdr));
 		if (copym == NULL)