[IPSEC]: Document that policy direction is derived from the index.

Here is a patch that adds a helper called xfrm_policy_id2dir to
document the fact that the policy direction can be and is derived
from the index.

This is based on a patch by YOSHIFUJI Hideaki and 210313105@suda.edu.cn.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 7564b2ce449f..b6e72f890c6c 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -931,4 +931,9 @@ static inline int xfrm_addr_cmp(xfrm_address_t *a, xfrm_address_t *b,
         }
 }
 
+static inline int xfrm_policy_id2dir(u32 index)
+{
+        return index & 7;
+}
+
 #endif  /* _NET_XFRM_H */