[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;
 		}
 	}