netdev - [PATCH][net-next] ipv6: drop container_of when convert dst to rt6

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Date:   Sun, 30 Sep 2018 13:02:52 +0800
From:   Li RongQing <lirongqing@...du.com>
To:     netdev@...r.kernel.org
Subject: [PATCH][net-next] ipv6: drop container_of when convert dst to rt6_info

we can save container_of computation and return dst directly,
since dst is always first member of struct rt6_info

Add a BUILD_BUG_ON() to catch any change that could break this
assertion.

Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 include/net/ip6_route.h | 4 +++-
 net/ipv6/route.c        | 6 +++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 7b9c82de11cc..1f09298634cb 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -194,8 +194,10 @@ static inline const struct rt6_info *skb_rt6_info(const struct sk_buff *skb)
 	const struct dst_entry *dst = skb_dst(skb);
 	const struct rt6_info *rt6 = NULL;
 
+	BUILD_BUG_ON(offsetof(struct rt6_info, dst) != 0);
+
 	if (dst)
-		rt6 = container_of(dst, struct rt6_info, dst);
+		rt6 = (struct rt6_info *)dst;
 
 	return rt6;
 }
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d28f83e01593..3fb8034fc2d0 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -217,7 +217,7 @@ static struct neighbour *ip6_dst_neigh_lookup(const struct dst_entry *dst,
 					      struct sk_buff *skb,
 					      const void *daddr)
 {
-	const struct rt6_info *rt = container_of(dst, struct rt6_info, dst);
+	const struct rt6_info *rt = (struct rt6_info *)dst;
 
 	return ip6_neigh_lookup(&rt->rt6i_gateway, dst->dev, skb, daddr);
 }
@@ -2187,7 +2187,7 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
 	struct fib6_info *from;
 	struct rt6_info *rt;
 
-	rt = container_of(dst, struct rt6_info, dst);
+	rt = (struct rt6_info *)dst;
 
 	rcu_read_lock();
 
@@ -4911,7 +4911,7 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	}
 
 
-	rt = container_of(dst, struct rt6_info, dst);
+	rt = (struct rt6_info *)dst;
 	if (rt->dst.error) {
 		err = rt->dst.error;
 		ip6_rt_put(rt);
-- 
2.16.2