net: sock: introduce sock_queue_rcv_skb_reason()

In order to report the reasons of skb drops in 'sock_queue_rcv_skb()',
introduce the function 'sock_queue_rcv_skb_reason()'.

As the return value of 'sock_queue_rcv_skb()' is used as the error code,
we can't make it as drop reason and have to pass extra output argument.
'sock_queue_rcv_skb()' is used in many places, so we can't change it
directly.

Introduce the new function 'sock_queue_rcv_skb_reason()' and make
'sock_queue_rcv_skb()' an inline call to it.
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2392,7 +2392,14 @@ int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
-int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
+
+int sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb,
+			      enum skb_drop_reason *reason);
+
+static inline int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
+{
+	return sock_queue_rcv_skb_reason(sk, skb, NULL);
+}
 
 int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb);
 struct sk_buff *sock_dequeue_err_skb(struct sock *sk);

net/core/sock.c

@@ -505,17 +505,35 @@ int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(__sock_queue_rcv_skb);
 
-int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
+int sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb,
+			      enum skb_drop_reason *reason)
 {
+	enum skb_drop_reason drop_reason;
 	int err;
 
 	err = sk_filter(sk, skb);
-	if (err)
-		return err;
-
-	return __sock_queue_rcv_skb(sk, skb);
+	if (err) {
+		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
+		goto out;
+	}
+	err = __sock_queue_rcv_skb(sk, skb);
+	switch (err) {
+	case -ENOMEM:
+		drop_reason = SKB_DROP_REASON_SOCKET_RCVBUFF;
+		break;
+	case -ENOBUFS:
+		drop_reason = SKB_DROP_REASON_PROTO_MEM;
+		break;
+	default:
+		drop_reason = SKB_NOT_DROPPED_YET;
+		break;
+	}
+out:
+	if (reason)
+		*reason = drop_reason;
+	return err;
 }
-EXPORT_SYMBOL(sock_queue_rcv_skb);
+EXPORT_SYMBOL(sock_queue_rcv_skb_reason);
 
 int __sk_receive_skb(struct sock *sk, struct sk_buff *skb,
 		     const int nested, unsigned int trim_cap, bool refcounted)