[NET]: Use non-recursive algorithm in skb_copy_datagram_iovec()

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>

1 files changed, 26 insertions, 55 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index da9bf71421a7..81987df536eb 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -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;
 }