diff --git a/src/libs/compat/freebsd11_network/compat/sys/mbuf.h b/src/libs/compat/freebsd11_network/compat/sys/mbuf.h
index 302bdbed08..eb767edfd9 100644
--- a/src/libs/compat/freebsd11_network/compat/sys/mbuf.h
+++ b/src/libs/compat/freebsd11_network/compat/sys/mbuf.h
@@ -81,6 +81,9 @@
 
 #define MTAG_PERSISTENT	0x800
 
+#define	M_COPYALL	1000000000
+	// Length to m_copy to copy all.
+
 #define EXT_CLUSTER		1		// 2048 bytes
 #define EXT_JUMBOP		4		// Page size
 #define EXT_JUMBO9		5		// 9 * 1024 bytes
@@ -189,6 +192,7 @@ struct mbuf*	m_collapse(struct mbuf*, int, int);
 void			m_copyback(struct mbuf*, int, int, caddr_t);
 void			m_copydata(const struct mbuf*, int, int, caddr_t);
 struct mbuf*	m_copypacket(struct mbuf*, int);
+struct mbuf *	m_copym(struct mbuf *m, int off0, int len, int wait);
 struct mbuf*	m_defrag(struct mbuf*, int);
 struct mbuf*	m_devget(char*, int, int, struct ifnet*,
 	void(*) (char*, caddr_t, u_int));
diff --git a/src/libs/compat/freebsd11_network/compat/sys/param.h b/src/libs/compat/freebsd11_network/compat/sys/param.h
index 36bdd29c54..336ad4cbcd 100644
--- a/src/libs/compat/freebsd11_network/compat/sys/param.h
+++ b/src/libs/compat/freebsd11_network/compat/sys/param.h
@@ -64,6 +64,7 @@
 #define roundup(x, y)	((((x)+((y)-1))/(y))*(y))  /* to any y */
 #define roundup2(x, y)	(((x) + ((y) - 1)) & (~((y) - 1)))
 #define rounddown(x, y)  (((x) / (y)) * (y))
+#define rounddown2(x, y) ((x)&(~((y)-1)))          /* if y is power of two */
 
 #define	PRIMASK	0x0ff
 #define	PCATCH	0x100
diff --git a/src/libs/compat/freebsd11_network/fbsd_mbuf.c b/src/libs/compat/freebsd11_network/fbsd_mbuf.c
index ca0cc819a8..443603abae 100644
--- a/src/libs/compat/freebsd11_network/fbsd_mbuf.c
+++ b/src/libs/compat/freebsd11_network/fbsd_mbuf.c
@@ -662,6 +662,77 @@ mb_dupcl(struct mbuf *n, struct mbuf *m)
 	n->m_flags |= M_EXT;
 }
 
+/*
+ * Make a copy of an mbuf chain starting "off0" bytes from the beginning,
+ * continuing for "len" bytes.  If len is M_COPYALL, copy to end of mbuf.
+ * The wait parameter is a choice of M_WAITOK/M_NOWAIT from caller.
+ * Note that the copy is read-only, because clusters are not copied,
+ * only their reference counts are incremented.
+ */
+struct mbuf *
+m_copym(struct mbuf *m, int off0, int len, int wait)
+{
+	struct mbuf *n, **np;
+	int off = off0;
+	struct mbuf *top;
+	int copyhdr = 0;
+
+	KASSERT(off >= 0, ("m_copym, negative off %d", off));
+	KASSERT(len >= 0, ("m_copym, negative len %d", len));
+	MBUF_CHECKSLEEP(wait);
+	if (off == 0 && m->m_flags & M_PKTHDR)
+		copyhdr = 1;
+	while (off > 0) {
+		KASSERT(m != NULL, ("m_copym, offset > size of mbuf chain"));
+		if (off < m->m_len)
+			break;
+		off -= m->m_len;
+		m = m->m_next;
+	}
+	np = &top;
+	top = NULL;
+	while (len > 0) {
+		if (m == NULL) {
+			KASSERT(len == M_COPYALL,
+				("m_copym, length > size of mbuf chain"));
+			break;
+		}
+		if (copyhdr)
+			n = m_gethdr(wait, m->m_type);
+		else
+			n = m_get(wait, m->m_type);
+		*np = n;
+		if (n == NULL)
+			goto nospace;
+		if (copyhdr) {
+			if (!m_dup_pkthdr(n, m, wait))
+				goto nospace;
+			if (len == M_COPYALL)
+				n->m_pkthdr.len -= off0;
+			else
+				n->m_pkthdr.len = len;
+			copyhdr = 0;
+		}
+		n->m_len = min(len, m->m_len - off);
+		if (m->m_flags & M_EXT) {
+			n->m_data = m->m_data + off;
+			mb_dupcl(n, m);
+		} else
+			bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
+				(u_int)n->m_len);
+		if (len != M_COPYALL)
+			len -= n->m_len;
+		off = 0;
+		m = m->m_next;
+		np = &n->m_next;
+	}
+
+	return (top);
+nospace:
+	m_freem(top);
+	return (NULL);
+}
+
 void
 m_demote_pkthdr(struct mbuf *m)
 {