skb: add some helpers for skb drop reasons

In order to simply the definition and assignment for
'enum skb_drop_reason', introduce some helpers.

SKB_DR() is used to define a variable of type 'enum skb_drop_reason'
with the 'SKB_DROP_REASON_NOT_SPECIFIED' initial value.

SKB_DR_SET() is used to set the value of the variable. Seems it is
a little useless? But it makes the code shorter.

SKB_DR_OR() is used to set the value of the variable if it is not set
yet, which means its value is SKB_DROP_REASON_NOT_SPECIFIED.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9b81ba4..0cbd6ad 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -450,6 +450,18 @@ enum skb_drop_reason {
        SKB_DROP_REASON_MAX,
 };
 
+#define SKB_DR_INIT(name, reason)                              \
+       enum skb_drop_reason name = SKB_DROP_REASON_##reason
+#define SKB_DR(name)                                           \
+       SKB_DR_INIT(name, NOT_SPECIFIED)
+#define SKB_DR_SET(name, reason)                               \
+       (name = SKB_DROP_REASON_##reason)
+#define SKB_DR_OR(name, reason)                                        \
+       do {                                                    \
+               if (name == SKB_DROP_REASON_NOT_SPECIFIED)      \
+                       SKB_DR_SET(name, reason);               \
+       } while (0)
+
 /* To allow 64K frame to be packed as single skb without frag_list we
  * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
  * buffers which do not start on a page boundary.