Remove inlined m_tag_free(). Rename _m_tag_free() to m_tag_free()

and make it visible (same way as in OpenBSD). Describe usage in manpage.

This change is useful for creating custom free methods, which
call default free method at their end.

While here, make malloc declaration for mbuf tags more informative.

Approved by:	julian (mentor), sam
MFC after:	1 month

3 files changed, 23 insertions, 22 deletions

diff --git a/share/man/man9/mbuf_tags.9 b/share/man/man9/mbuf_tags.9
index ab74791..6992b05 100644
--- a/share/man/man9/mbuf_tags.9
+++ b/share/man/man9/mbuf_tags.9
@@ -91,8 +91,7 @@ fields are set to type, length,
 and
 cookie, respectively.
 .Va m_tag_free
-points to
-.Xr free 9 .
+points to a function which will be used to free this tag.
 Following this structure are
 .Va m_tag_len
 bytes of space that can be used to store tag-specific information.
@@ -194,11 +193,16 @@ Return the first tag associated with
 .It Fn m_tag_free tag
 Free
 .Fa tag
-using its
-.Va m_tag_free
-method.
-.Xr free 9
-is used by default.
+using default free method.
+This function should only be used at the end of a custom free method.
+It should never be used to free a packet tag of an unknown origination.
+To perform the latter
+.Fn m_tag_delete
+should be used in case of an attached
+.Fa tag
+or (tag->m_tag_free)(tag)
+should be called in case of a detached
+.Fa tag .
 .It Fn m_tag_init mbuf
 Initialize the tag storage for packet
 .Fa mbuf .
diff --git a/sys/kern/uipc_mbuf2.c b/sys/kern/uipc_mbuf2.c
index f5a35ca..52019ad 100644
--- a/sys/kern/uipc_mbuf2.c
+++ b/sys/kern/uipc_mbuf2.c
@@ -76,7 +76,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mbuf.h>
 #include <sys/mutex.h>
 
-MALLOC_DEFINE(M_PACKET_TAGS, "tag", "packet-attached information");
+MALLOC_DEFINE(M_PACKET_TAGS, "mbuf tags", "packet-attached information");
 
 /* can't call it m_dup(), as freebsd[34] uses m_dup() with different arg */
 static struct mbuf *m_dup1(struct mbuf *, int, int, int);
@@ -301,9 +301,14 @@ m_dup1(struct mbuf *m, int off, int len, int wait)
 	return n;
 }
 
-/* Free a packet tag. */
-static void
-_m_tag_free(struct m_tag *t)
+/*
+ * Free a packet tag.
+ * This function should not be called directly, unless you know what you
+ * are doing. Use m_tag_delete() or (t->m_tag_free)(t) instead, when you
+ * work with a tag that you haven't allocated yourself.
+ */
+void
+m_tag_free(struct m_tag *t)
 {
 #ifdef MAC
 	if (t->m_tag_id == PACKET_TAG_MACLABEL)
@@ -325,7 +330,7 @@ m_tag_alloc(u_int32_t cookie, int type, int len, int wait)
 	if (t == NULL)
 		return NULL;
 	m_tag_setup(t, cookie, type, len);
-	t->m_tag_free = _m_tag_free;
+	t->m_tag_free = m_tag_free;
 	return t;
 }
 
@@ -336,7 +341,7 @@ m_tag_delete(struct mbuf *m, struct m_tag *t)
 
 	KASSERT(m && t, ("m_tag_delete: null argument, m %p t %p", m, t));
 	m_tag_unlink(m, t);
-	m_tag_free(t);
+	(t->m_tag_free)(t);
 }
 
 /* Unlink and free a packet tag chain, starting from given tag. */
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 78053e9..990521f 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -648,6 +648,7 @@ struct	mbuf	*m_uiotombuf(struct uio *, int, int);
 struct	m_tag	*m_tag_alloc(u_int32_t, int, int, int);
 void		 m_tag_delete(struct mbuf *, struct m_tag *);
 void		 m_tag_delete_chain(struct mbuf *, struct m_tag *);
+void		 m_tag_free(struct m_tag *);
 struct	m_tag	*m_tag_locate(struct mbuf *, u_int32_t, int, struct m_tag *);
 struct	m_tag	*m_tag_copy(struct m_tag *, int);
 int		 m_tag_copy_chain(struct mbuf *, struct mbuf *, int);
@@ -678,15 +679,6 @@ m_tag_setup(struct m_tag *t, u_int32_t cookie, int type, int len)
 }
 
 /*
- * Reclaim resources associated with a tag.
- */
-static __inline void
-m_tag_free(struct m_tag *t)
-{
-	(*t->m_tag_free)(t);
-}
-
-/*
  * Return the first tag associated with an mbuf.
  */
 static __inline struct m_tag *