[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, 9 insertions, 16 deletions

diff --git a/net/core/user_dma.c b/net/core/user_dma.c
index 0ad1cd57bc3..89241cdeea3 100644
--- a/net/core/user_dma.c
+++ b/net/core/user_dma.c
@@ -49,8 +49,8 @@ int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
                         struct sk_buff *skb, int offset, struct iovec *to,
                         size_t len, struct dma_pinned_list *pinned_list)
 {
-        int start = skb_headlen(skb);
-        int i, copy = start - offset;
+        int end = skb_headlen(skb);
+        int i, copy = end - offset;
         dma_cookie_t cookie = 0;
 
         /* Copy header. */
@@ -69,11 +69,9 @@ int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
 
         /* Copy paged appendix. Hmm... why does this look so complicated? */
         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;
                 copy = end - offset;
                 if ((copy = end - offset) > 0) {
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
@@ -82,8 +80,8 @@ int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
                         if (copy > len)
                                 copy = len;
 
-                        cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list, page,
-                                        frag->page_offset + offset - start, copy);
+                        cookie = dma_memcpy_pg_to_iovec(chan, to, pinned_list,
+                                        page, frag->page_offset, copy);
                         if (cookie < 0)
                                 goto fault;
                         len -= copy;
@@ -91,25 +89,21 @@ int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
                                 goto end;
                         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;
                         copy = end - offset;
                         if (copy > 0) {
                                 if (copy > len)
                                         copy = len;
                                 cookie = dma_skb_copy_datagram_iovec(chan, list,
-                                                offset - start, to, copy,
-                                                pinned_list);
+                                                0, to, copy, pinned_list);
                                 if (cookie < 0)
                                         goto fault;
                                 len -= copy;
@@ -117,7 +111,6 @@ int dma_skb_copy_datagram_iovec(struct dma_chan *chan,
                                         goto end;
                                 offset += copy;
                         }
-                        start = end;
                 }
         }