static unsigned long atalk_sum_skb(const struct sk_buff *skb, int offset,
				   int len, unsigned long sum)
{
	int start = skb_headlen(skb);
	int i, copy;

	/* checksum stuff in header space */
	if ( (copy = start - offset) > 0) {
		if (copy > len)
			copy = len;
		sum = atalk_sum_partial(skb->data + offset, copy, sum);
		if ( (len -= copy) == 0) 
			return sum;

		offset += copy;
	}

	/* checksum stuff in frags */
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		int end;

		BUG_TRAP(start <= offset + len);

		end = start + skb_shinfo(skb)->frags[i].size;
		if ((copy = end - offset) > 0) {
			u8 *vaddr;
			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

			if (copy > len)
				copy = len;
			vaddr = kmap_skb_frag(frag);
			sum = atalk_sum_partial(vaddr + frag->page_offset +
						  offset - start, copy, sum);
			kunmap_skb_frag(vaddr);

			if (!(len -= copy))
				return sum;
			offset += copy;
		}
		start = end;
	}

	if (skb_shinfo(skb)->frag_list) {
		struct sk_buff *list = skb_shinfo(skb)->frag_list;

		for (; list; list = list->next) {
			int end;

			BUG_TRAP(start <= offset + len);

			end = start + list->len;
			if ((copy = end - offset) > 0) {
				if (copy > len)
					copy = len;
				sum = atalk_sum_skb(list, offset - start,
						    copy, sum);
				if ((len -= copy) == 0)
					return sum;
				offset += copy;
			}
			start = end;
		}
	}

	BUG_ON(len > 0);

	return sum;
}
static unsigned long atalk_sum_skb(const struct sk_buff *skb, int offset,
				   int len, unsigned long sum)
{
	int start = skb_headlen(skb);
	int i, copy;

	 
	if ( (copy = start - offset) > 0) {
		if (copy > len)
			copy = len;
		sum = atalk_sum_partial(skb->data + offset, copy, sum);
		if ( (len -= copy) == 0) 
			return sum;

		offset += copy;
	}

	 
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		int end;

		BUG_TRAP(start <= offset + len);

		end = start + skb_shinfo(skb)->frags[i].size;
		if ((copy = end - offset) > 0) {
			u8 *vaddr;
			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

			if (copy > len)
				copy = len;
			vaddr = kmap_skb_frag(frag);
			sum = atalk_sum_partial(vaddr + frag->page_offset +
						  offset - start, copy, sum);
			kunmap_skb_frag(vaddr);

			if (!(len -= copy))
				return sum;
			offset += copy;
		}
		start = end;
	}

	if (skb_shinfo(skb)->frag_list) {
		struct sk_buff *list = skb_shinfo(skb)->frag_list;

		for (; list; list = list->next) {
			int end;

			BUG_TRAP(start <= offset + len);

			end = start + list->len;
			if ((copy = end - offset) > 0) {
				if (copy > len)
					copy = len;
				sum = atalk_sum_skb(list, offset - start,
						    copy, sum);
				if ((len -= copy) == 0)
					return sum;
				offset += copy;
			}
			start = end;
		}
	}

	BUG_ON(len > 0);

	return sum;
}