[NET]: Clean up sk_buff walkers.

I noticed recently that, in skb_checksum(), "offset" and "start" are
essentially the same thing and have the same value throughout the
function, despite being computed differently. Using a single variable
allows some cleanups and makes the skb_checksum() function smaller,
more readable, and presumably marginally faster.

We appear to have many other "sk_buff walker" functions built on the
exact same model, so the cleanup applies to them, too. Here is a list
of the functions I found to be affected:

net/appletalk/ddp.c:atalk_sum_skb()
net/core/datagram.c:skb_copy_datagram_iovec()
net/core/datagram.c:skb_copy_and_csum_datagram()
net/core/skbuff.c:skb_copy_bits()
net/core/skbuff.c:skb_store_bits()
net/core/skbuff.c:skb_checksum()
net/core/skbuff.c:skb_copy_and_csum_bit()
net/core/user_dma.c:dma_skb_copy_datagram_iovec()
net/xfrm/xfrm_algo.c:skb_icv_walk()
net/xfrm/xfrm_algo.c:skb_to_sgvec()

OTOH, I admit I'm a bit surprised, the cleanup is rather obvious so I'm
really wondering if I am missing something. Can anyone please comment
on this?

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 14 deletions

diff --git a/net/xfrm/xfrm_algo.c b/net/xfrm/xfrm_algo.c
index 6249a9405bb8..be529c4241a6 100644
--- a/net/xfrm/xfrm_algo.c
+++ b/net/xfrm/xfrm_algo.c
@@ -532,8 +532,8 @@ EXPORT_SYMBOL_GPL(xfrm_count_enc_supported);
 int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                  int offset, int len, icv_update_fn_t icv_update)
 {
-        int start = skb_headlen(skb);
-        int i, copy = start - offset;
+        int end = skb_headlen(skb);
+        int i, copy = end - offset;
         int err;
         struct scatterlist sg;
 
@@ -556,11 +556,9 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
         }
 
         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-                int end;
+                BUG_TRAP(len >= 0);
 
-                BUG_TRAP(start <= offset + len);
-
-                end = start + skb_shinfo(skb)->frags[i].size;
+                end = offset + skb_shinfo(skb)->frags[i].size;
                 if ((copy = end - offset) > 0) {
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
@@ -568,7 +566,7 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                 copy = len;
 
                         sg.page = frag->page;
-                        sg.offset = frag->page_offset + offset-start;
+                        sg.offset = frag->page_offset;
                         sg.length = copy;
 
                         err = icv_update(desc, &sg, copy);
@@ -579,22 +577,19 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                 return 0;
                         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);
+                        BUG_TRAP(len >= 0);
 
-                        end = start + list->len;
+                        end = offset + list->len;
                         if ((copy = end - offset) > 0) {
                                 if (copy > len)
                                         copy = len;
-                                err = skb_icv_walk(list, desc, offset-start,
+                                err = skb_icv_walk(list, desc, 0,
                                                    copy, icv_update);
                                 if (unlikely(err))
                                         return err;
@@ -602,7 +597,6 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                         return 0;
                                 offset += copy;
                         }
-                        start = end;
                 }
         }
         BUG_ON(len);