[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/appletalk/ddp.c b/net/appletalk/ddp.c
index f6a92a0b7aa6..16eda21fb38c 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -937,11 +937,11 @@ static unsigned long atalk_sum_partial(const unsigned char *data,
 static unsigned long atalk_sum_skb(const struct sk_buff *skb, int offset,
                                    int len, unsigned long sum)
 {
-        int start = skb_headlen(skb);
+        int end = skb_headlen(skb);
         int i, copy;
 
         /* checksum stuff in header space */
-        if ( (copy = start - offset) > 0) {
+        if ((copy = end - offset) > 0) {
                 if (copy > len)
                         copy = len;
                 sum = atalk_sum_partial(skb->data + offset, copy, sum);
@@ -953,11 +953,9 @@ static unsigned long atalk_sum_skb(const struct sk_buff *skb, int offset,
 
         /* checksum stuff in frags */
         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) {
                         u8 *vaddr;
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
@@ -965,36 +963,31 @@ static unsigned long atalk_sum_skb(const struct sk_buff *skb, int offset,
                         if (copy > len)
                                 copy = len;
                         vaddr = kmap_skb_frag(frag);
-                        sum = atalk_sum_partial(vaddr + frag->page_offset +
-                                                  offset - start, copy, sum);
+                        sum = atalk_sum_partial(vaddr + frag->page_offset,
+                                                copy, sum);
                         kunmap_skb_frag(vaddr);
 
                         if (!(len -= copy))
                                 return sum;
                         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;
-                                sum = atalk_sum_skb(list, offset - start,
-                                                    copy, sum);
+                                sum = atalk_sum_skb(list, 0, copy, sum);
                                 if ((len -= copy) == 0)
                                         return sum;
                                 offset += copy;
                         }
-                        start = end;
                 }
         }