+/* Unfortunately this function is not exported so this is a verbatim copy
+ * from net/core/datagram.c in 2.6.30. */
+static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
+ u8 __user *to, int len,
+ __wsum *csump)
+{
+ int start = skb_headlen(skb);
+ int pos = 0;
+ int i, copy = start - offset;
+
+ /* Copy header. */
+ if (copy > 0) {
+ int err = 0;
+ if (copy > len)
+ copy = len;
+ *csump = csum_and_copy_to_user(skb->data + offset, to, copy,
+ *csump, &err);
+ if (err)
+ goto fault;
+ if ((len -= copy) == 0)
+ return 0;
+ offset += copy;
+ to += copy;
+ pos = copy;
+ }
+
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ int end;
+
+ WARN_ON(start > offset + len);
+
+ end = start + skb_shinfo(skb)->frags[i].size;
+ if ((copy = end - offset) > 0) {
+ __wsum csum2;
+ int err = 0;
+ u8 *vaddr;
+ skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ struct page *page = frag->page;
+
+ if (copy > len)
+ copy = len;
+ vaddr = kmap(page);
+ csum2 = csum_and_copy_to_user(vaddr +
+ frag->page_offset +
+ offset - start,
+ to, copy, 0, &err);
+ kunmap(page);
+ if (err)
+ goto fault;
+ *csump = csum_block_add(*csump, csum2, pos);
+ if (!(len -= copy))
+ return 0;
+ offset += copy;
+ to += copy;
+ pos += 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;
+
+ WARN_ON(start > offset + len);
+
+ end = start + list->len;
+ if ((copy = end - offset) > 0) {
+ __wsum csum2 = 0;
+ if (copy > len)
+ copy = len;
+ if (skb_copy_and_csum_datagram(list,
+ offset - start,
+ to, copy,
+ &csum2))
+ goto fault;
+ *csump = csum_block_add(*csump, csum2, pos);
+ if ((len -= copy) == 0)
+ return 0;
+ offset += copy;
+ to += copy;
+ pos += copy;
+ }
+ start = end;
+ }
+ }
+ if (!len)
+ return 0;
+
+fault:
+ return -EFAULT;
+}
+