[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 0ad1cd5..89241cd 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;
 		}
 	}