Introduce the function skb_vlan_inet_prepare_reason() and make
skb_vlan_inet_prepare an inline call to it. The drop reasons of it just
come from pskb_may_pull_reason.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
v3:
- fix some format problems,  as Alexander advised
---
 include/net/ip_tunnels.h | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index 7fc2f7bf837a..d00d8835e789 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -465,13 +465,14 @@ static inline bool pskb_inet_may_pull(struct sk_buff *skb)
 	return pskb_inet_may_pull_reason(skb) == SKB_NOT_DROPPED_YET;
 }
 
-/* Variant of pskb_inet_may_pull().
+/* Variant of pskb_inet_may_pull_reason().
  */
-static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
-					 bool inner_proto_inherit)
+static inline enum skb_drop_reason
+skb_vlan_inet_prepare_reason(struct sk_buff *skb, bool inner_proto_inherit)
 {
 	int nhlen = 0, maclen = inner_proto_inherit ? 0 : ETH_HLEN;
 	__be16 type = skb->protocol;
+	enum skb_drop_reason reason;
 
 	/* Essentially this is skb_protocol(skb, true)
 	 * And we get MAC len.
@@ -492,11 +493,20 @@ static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
 	/* For ETH_P_IPV6/ETH_P_IP we make sure to pull
 	 * a base network header in skb->head.
 	 */
-	if (!pskb_may_pull(skb, maclen + nhlen))
-		return false;
+	reason = pskb_may_pull_reason(skb, maclen + nhlen);
+	if (reason)
+		return reason;
 
 	skb_set_network_header(skb, maclen);
-	return true;
+
+	return SKB_NOT_DROPPED_YET;
+}
+
+static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
+					 bool inner_proto_inherit)
+{
+	return skb_vlan_inet_prepare_reason(skb, inner_proto_inherit) ==
+	       SKB_NOT_DROPPED_YET;
 }
 
 static inline int ip_encap_hlen(struct ip_tunnel_encap *e)
-- 
2.39.2