Name: skb_walk Function
Status: Untested
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

There's no convenient function to walk the data of an skbuff; provide
one.  Netfilter extensions in particular can use this to examine
packet contents.

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .18220-linux-2.6.7-rc3-bk7/net/core/skbuff.c .18220-linux-2.6.7-rc3-bk7.updated/net/core/skbuff.c
--- .18220-linux-2.6.7-rc3-bk7/net/core/skbuff.c	2004-05-10 15:14:04.000000000 +1000
+++ .18220-linux-2.6.7-rc3-bk7.updated/net/core/skbuff.c	2004-06-16 09:59:46.000000000 +1000
@@ -1210,6 +1210,54 @@ void skb_unlink(struct sk_buff *skb)
 	}
 }
 
+static int __skb_walk(struct sk_buff *skb,
+		      struct sk_buff *master,
+		      int (*fn)(struct sk_buff *, void *, int, void *),
+		      void *arg)
+{
+	struct sk_buff *list;
+	int i, ret;
+
+	ret = fn(master, skb->data, skb_headlen(skb), arg);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+		u8 *vaddr;
+		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+
+		vaddr = kmap_skb_frag(frag);
+		ret = fn(master, vaddr + frag->page_offset, frag->size, arg);
+		kunmap_skb_frag(vaddr);
+		if (ret)
+			return ret;
+	}
+
+	for (list = skb_shinfo(skb)->frag_list; list; list = list->next) {
+		ret = __skb_walk(list, master, fn, arg);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
+/**
+ *	skb_walk	-	interate through a buffer
+ *	@skb: buffer to iterate over
+ *	@fn: function which takes skb, ptr, length and @arg
+ *	@arg: final argument to pass through to @fn
+ *
+ *	Iterates fairly efficiently through a (possibly nonlinear)
+ *	@skb; returns the value of @fn, and stops if @fn returns
+ *	non-zero.
+ */
+int skb_walk(struct sk_buff *skb,
+	     int (*fn)(struct sk_buff *, void *, int, void *),
+	     void *arg)
+{
+	return __skb_walk(skb, skb, fn, arg);
+}
+
 
 /**
  *	skb_append	-	append a buffer