freebsd_network: Fix and implement some mbuf functions.

Spotted while reviewing the code during iflib porting.

src/libs/compat/freebsd_network/compat/sys/mbuf.h

@@ -294,8 +294,9 @@ int				m_dup_pkthdr(struct mbuf *to, const struct mbuf *from, int how);
 void			m_demote_pkthdr(struct mbuf *m);
 void			m_demote(struct mbuf *m0, int all, int flags);
 
-void			m_extadd(struct mbuf*, caddr_t, u_int, void(*) (void*, void*),
-	void*, void*, int, int);
+void			m_extadd(struct mbuf *mb, caddr_t buf, u_int size,
+	void (*freef)(struct mbuf *, void *, void *), void *arg1, void *arg2,
+	int flags, int type);
 
 u_int			m_fixhdr(struct mbuf*);
 struct mbuf*	m_free(struct mbuf*);

src/libs/compat/freebsd_network/fbsd_kern_mbuf.c

@@ -95,3 +95,61 @@ m_getm2(struct mbuf *m, int len, int how, short type, int flags)
 	return (m);
 }
 
+/*-
+ * Configure a provided mbuf to refer to the provided external storage
+ * buffer and setup a reference count for said buffer.
+ *
+ * Arguments:
+ *    mb     The existing mbuf to which to attach the provided buffer.
+ *    buf    The address of the provided external storage buffer.
+ *    size   The size of the provided buffer.
+ *    freef  A pointer to a routine that is responsible for freeing the
+ *           provided external storage buffer.
+ *    args   A pointer to an argument structure (of any type) to be passed
+ *           to the provided freef routine (may be NULL).
+ *    flags  Any other flags to be passed to the provided mbuf.
+ *    type   The type that the external storage buffer should be
+ *           labeled with.
+ *
+ * Returns:
+ *    Nothing.
+ */
+void
+m_extadd(struct mbuf *mb, caddr_t buf, u_int size,
+    void (*freef)(struct mbuf *, void *, void *), void *arg1, void *arg2,
+    int flags, int type)
+{
+
+	KASSERT(type != EXT_CLUSTER, ("%s: EXT_CLUSTER not allowed", __func__));
+
+	mb->m_flags |= (M_EXT | flags);
+	mb->m_ext.ext_buf = buf;
+	mb->m_data = mb->m_ext.ext_buf;
+	mb->m_ext.ext_size = size;
+#ifndef __HAIKU__
+	mb->m_ext.ext_free = freef;
+	mb->m_ext.ext_arg1 = arg1;
+	mb->m_ext.ext_arg2 = arg2;
+#else
+	if (freef != NULL)
+		panic("m_ext.ext_free not yet implemented");
+#endif
+	mb->m_ext.ext_type = type;
+
+	if (type != EXT_EXTREF) {
+		mb->m_ext.ext_count = 1;
+		mb->m_ext.ext_flags = EXT_FLAG_EMBREF;
+	} else
+		mb->m_ext.ext_flags = 0;
+}
+
+/*
+ * Free an entire chain of mbufs and associated external buffers, if
+ * applicable.
+ */
+void
+m_freem(struct mbuf *mb)
+{
+	while (mb != NULL)
+		mb = m_free(mb);
+}

src/libs/compat/freebsd_network/mbuf.c

@@ -214,15 +214,6 @@ m_cljget(struct mbuf *memoryBuffer, int how, int size)
 	return NULL;
 }
 
-
-void
-m_freem(struct mbuf *memoryBuffer)
-{
-	while (memoryBuffer)
-		memoryBuffer = m_free(memoryBuffer);
-}
-
-
 static void
 mb_free_ext(struct mbuf *memoryBuffer)
 {
@@ -272,7 +263,7 @@ mb_free_ext(struct mbuf *memoryBuffer)
 	else if (memoryBuffer->m_ext.ext_type == EXT_JUMBOP)
 		cache = sJumboPageSizeCache;
 	else
-		panic("unknown type");
+		panic("unknown mbuf ext_type %d", memoryBuffer->m_ext.ext_type);
 
 	object_cache_free(cache, memoryBuffer->m_ext.ext_buf, 0);
 	memoryBuffer->m_ext.ext_buf = NULL;
@@ -281,28 +272,21 @@ mb_free_ext(struct mbuf *memoryBuffer)
 
 
 struct mbuf *
-m_free(struct mbuf *memoryBuffer)
+m_free(struct mbuf* memoryBuffer)
 {
-	struct mbuf *next = memoryBuffer->m_next;
+	struct mbuf* next = memoryBuffer->m_next;
 
+	if ((memoryBuffer->m_flags & (M_PKTHDR|M_NOFREE)) == (M_PKTHDR|M_NOFREE))
+		m_tag_delete_chain(memoryBuffer, NULL);
 	if (memoryBuffer->m_flags & M_EXT)
 		mb_free_ext(memoryBuffer);
-	else
+	else if ((memoryBuffer->m_flags & M_NOFREE) == 0)
 		object_cache_free(sMBufCache, memoryBuffer, 0);
 
 	return next;
 }
 
 
-void
-m_extadd(struct mbuf *memoryBuffer, caddr_t buffer, u_int size,
-    void (*freeHook)(void *, void *), void *arg1, void *arg2, int flags, int type)
-{
-	// TODO: implement?
-	panic("m_extadd() called.");
-}
-
-
 status_t
 init_mbufs()
 {