[NET]: Use non-recursive algorithm in skb_copy_datagram_iovec()
Daniel Phillips [Tue, 27 Sep 2005 22:22:35 +0000 (15:22 -0700)]
Use iteration instead of recursion.  Fraglists within fraglists
should never occur, so we BUG check this.

Signed-off-by: Daniel Phillips <phillips@istop.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/datagram.c

index da9bf71..81987df 100644 (file)
@@ -211,74 +211,45 @@ void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
 int skb_copy_datagram_iovec(const struct sk_buff *skb, int offset,
                            struct iovec *to, int len)
 {
-       int start = skb_headlen(skb);
-       int i, copy = start - offset;
-
-       /* Copy header. */
-       if (copy > 0) {
-               if (copy > len)
-                       copy = len;
-               if (memcpy_toiovec(to, skb->data + offset, copy))
-                       goto fault;
-               if ((len -= copy) == 0)
-                       return 0;
-               offset += copy;
-       }
+       int i, err, fraglen, end = 0;
+       struct sk_buff *next = skb_shinfo(skb)->frag_list;
+next_skb:
+       fraglen = skb_headlen(skb);
+       i = -1;
 
-       /* Copy paged appendix. Hmm... why does this look so complicated? */
-       for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-               int end;
-
-               BUG_TRAP(start <= offset + len);
+       while (1) {
+               int start = end;
 
-               end = start + skb_shinfo(skb)->frags[i].size;
-               if ((copy = end - offset) > 0) {
-                       int err;
-                       u8  *vaddr;
-                       skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
-                       struct page *page = frag->page;
+               if ((end += fraglen) > offset) {
+                       int copy = end - offset, o = offset - start;
 
                        if (copy > len)
                                copy = len;
-                       vaddr = kmap(page);
-                       err = memcpy_toiovec(to, vaddr + frag->page_offset +
-                                            offset - start, copy);
-                       kunmap(page);
+                       if (i == -1)
+                               err = memcpy_toiovec(to, skb->data + o, copy);
+                       else {
+                               skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+                               struct page *page = frag->page;
+                               void *p = kmap(page) + frag->page_offset + o;
+                               err = memcpy_toiovec(to, p, copy);
+                               kunmap(page);
+                       }
                        if (err)
                                goto fault;
                        if (!(len -= copy))
                                return 0;
                        offset += copy;
                }
-               start = end;
+               if (++i >= skb_shinfo(skb)->nr_frags)
+                       break;
+               fraglen = skb_shinfo(skb)->frags[i].size;
        }
-
-       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;
-                               if (skb_copy_datagram_iovec(list,
-                                                           offset - start,
-                                                           to, copy))
-                                       goto fault;
-                               if ((len -= copy) == 0)
-                                       return 0;
-                               offset += copy;
-                       }
-                       start = end;
-               }
+       if (next) {
+               skb = next;
+               BUG_ON(skb_shinfo(skb)->frag_list);
+               next = skb->next;
+               goto next_skb;
        }
-       if (!len)
-               return 0;
-
 fault:
        return -EFAULT;
 }