[PATCH v3] include/linux/skbuff.h: using '(__u16) ~0U' instead of'~0U'

[Chen Gang]

Both 'transport_header' and 'mac_header' are __u16, which are
never equal to '~0U'.

So need use '(__u16) ~0U' instead of '~0U'.

The related warning (with EXTRA_CFLAGS=-W ARCH=m68k for allmodconfig)
  include/linux/skbuff.h:1587:2: warning: comparison is always true due to limited range of data type [-Wtype-limits]
  ...

Use meaningful macro instead of hard code number, and better to
initialize 'skb->transport_header' in __alloc_skb_head(), too.



Signed-off-by: Chen Gang <gang.chen@xxxxxxxxxxx>
---
 include/linux/skbuff.h |    6 ++++--
 net/core/skbuff.c      |   11 ++++++-----
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5f93119..3314911 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -40,6 +40,8 @@
 #define CHECKSUM_COMPLETE 2
 #define CHECKSUM_PARTIAL 3
 
+#define SKB_HEADER_OFFSET_UNSET	((__u16) ~0U)
+
 #define SKB_DATA_ALIGN(X)	(((X) + (SMP_CACHE_BYTES - 1)) & \
 				 ~(SMP_CACHE_BYTES - 1))
 #define SKB_WITH_OVERHEAD(X)	\
@@ -1593,7 +1595,7 @@ 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 != SKB_HEADER_OFFSET_UNSET;
 }
 
 static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
@@ -1636,7 +1638,7 @@ 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 != SKB_HEADER_OFFSET_UNSET;
 }
 
 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..6808433 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -200,7 +200,8 @@ struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node)
 	atomic_set(&skb->users, 1);
 
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
+	skb->mac_header = SKB_HEADER_OFFSET_UNSET;
+	skb->transport_header = SKB_HEADER_OFFSET_UNSET;
 #endif
 out:
 	return skb;
@@ -276,8 +277,8 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 	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;
+	skb->mac_header = SKB_HEADER_OFFSET_UNSET;
+	skb->transport_header = SKB_HEADER_OFFSET_UNSET;
 #endif
 
 	/* make sure we initialize shinfo sequentially */
@@ -345,8 +346,8 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size)
 	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;
+	skb->mac_header = SKB_HEADER_OFFSET_UNSET;
+	skb->transport_header = SKB_HEADER_OFFSET_UNSET;
 #endif
 
 	/* make sure we initialize shinfo sequentially */
-- 
1.7.7.6
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