[Patch net-next v2] net: clean up skb headers code

[Patch net-next v2] net: clean up skb headers code

[Cong Wang]

From: Cong Wang <amwang@redhat.com>

commit 1a37e412a0225fcba5587 (net: Use 16bits for *_headers
fields of struct skbuff) converts skb->*_header to u16,
some #if NET_SKBUFF_DATA_USES_OFFSET are now useless,
and to be safe, we could just use "X = (typeof(X)) ~0U;"
as suggested by David.

Cc: David S. Miller <davem@davemloft.net>
Cc: Simon Horman <horms@verge.net.au>
Signed-off-by: Cong Wang <amwang@redhat.com>

---
v2: use typeof

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5f93119..b999790 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1593,7 +1593,7 @@ static inline void skb_set_inner_mac_header(struct sk_buff *skb,
 }
 static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
 {
-	return skb->transport_header != ~0U;
+	return skb->transport_header != (typeof(skb->transport_header))~0U;
 }
 
 static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
@@ -1636,7 +1636,7 @@ static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
 
 static inline int skb_mac_header_was_set(const struct sk_buff *skb)
 {
-	return skb->mac_header != ~0U;
+	return skb->mac_header != (typeof(skb->mac_header))~0U;
 }
 
 static inline void skb_reset_mac_header(struct sk_buff *skb)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f45de07..6b1b52c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -199,9 +199,7 @@ struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node)
 	skb->truesize = sizeof(struct sk_buff);
 	atomic_set(&skb->users, 1);
 
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
 out:
 	return skb;
 }
@@ -275,10 +273,8 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 	skb->data = data;
 	skb_reset_tail_pointer(skb);
 	skb->end = skb->tail + size;
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-	skb->transport_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
+	skb->transport_header = (typeof(skb->transport_header))~0U;
 
 	/* make sure we initialize shinfo sequentially */
 	shinfo = skb_shinfo(skb);
@@ -344,10 +340,8 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size)
 	skb->data = data;
 	skb_reset_tail_pointer(skb);
 	skb->end = skb->tail + size;
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-	skb->transport_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
+	skb->transport_header = (typeof(skb->transport_header))~0U;
 
 	/* make sure we initialize shinfo sequentially */
 	shinfo = skb_shinfo(skb);

Re: [Patch net-next v2] net: clean up skb headers code

[David Miller]

From: Cong Wang <amwang@redhat.com>
Date: Wed, 29 May 2013 15:16:05 +0800

> From: Cong Wang <amwang@redhat.com>
> 
> commit 1a37e412a0225fcba5587 (net: Use 16bits for *_headers
> fields of struct skbuff) converts skb->*_header to u16,
> some #if NET_SKBUFF_DATA_USES_OFFSET are now useless,
> and to be safe, we could just use "X = (typeof(X)) ~0U;"
> as suggested by David.
> 
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Simon Horman <horms@verge.net.au>
> Signed-off-by: Cong Wang <amwang@redhat.com>

After much internal deliberation, I still like this approach the
best because it prevents mistakes in the future.

Applied, thanks.