Index: kern/uipc_mbuf.c
===================================================================
RCS file: /cvsroot/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.153
diff -u -p -u -r1.153 uipc_mbuf.c
--- kern/uipc_mbuf.c	9 Oct 2013 20:15:20 -0000	1.153
+++ kern/uipc_mbuf.c	14 Nov 2013 00:34:53 -0000
@@ -722,6 +722,11 @@ m_dup(struct mbuf *m, int off0, int len,
 	return m_copym0(m, off0, len, wait, 1);	/* deep copy */
 }
 
+static inline int
+m_mbuflen(int len, int clen) {
+    return len == M_COPYALL ? clen : min(len, clen);
+}
+
 static struct mbuf *
 m_copym0(struct mbuf *m, int off0, int len, int wait, int deep)
 {
@@ -764,7 +769,7 @@ m_copym0(struct mbuf *m, int off0, int l
 				n->m_pkthdr.len = len;
 			copyhdr = 0;
 		}
-		n->m_len = min(len, m->m_len - off);
+		n->m_len = m_mbuflen(len, m->m_len - off);
 		if (m->m_flags & M_EXT) {
 			if (!deep) {
 				n->m_data = m->m_data + off;
@@ -776,7 +781,7 @@ m_copym0(struct mbuf *m, int off0, int l
 				 */
 				MCLGET(n, wait);
 				n->m_len = M_TRAILINGSPACE(n);
-				n->m_len = min(n->m_len, len);
+				n->m_len = m_mbuflen(len, n->m_len);
 				n->m_len = min(n->m_len, m->m_len - off);
 				memcpy(mtod(n, void *), mtod(m, char *) + off,
 				    (unsigned)n->m_len);
Index: sys/mbuf.h
===================================================================
RCS file: /cvsroot/src/sys/sys/mbuf.h,v
retrieving revision 1.152
diff -u -p -u -r1.152 mbuf.h
--- sys/mbuf.h	27 Jun 2013 17:47:18 -0000	1.152
+++ sys/mbuf.h	14 Nov 2013 00:34:54 -0000
@@ -686,7 +686,7 @@ do {									\
 } while (/* CONSTCOND */ 0)
 
 /* length to m_copy to copy all */
-#define	M_COPYALL	1000000000
+#define	M_COPYALL	-1
 
 /* compatibility with 4.3 */
 #define  m_copy(m, o, l)	m_copym((m), (o), (l), M_DONTWAIT)