tcp: prepare CC get_info() access from getsockopt()

We would like that optional info provided by Congestion Control
modules using netlink can also be read using getsockopt()

This patch changes get_info() to put this information in a buffer,
instead of skb, like tcp_get_info(), so that following patch
can reuse this common infrastructure.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index dd7b4ea..6d204f3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -804,6 +804,8 @@
 /* Requires ECN/ECT set on all packets */
 #define TCP_CONG_NEEDS_ECN	0x2
 
+union tcp_cc_info;
+
 struct tcp_congestion_ops {
 	struct list_head	list;
 	u32 key;
@@ -829,7 +831,8 @@
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
 	/* get info for inet_diag (optional) */
-	int (*get_info)(struct sock *sk, u32 ext, struct sk_buff *skb);
+	size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
+			   union tcp_cc_info *info);
 
 	char 		name[TCP_CA_NAME_MAX];
 	struct module 	*owner;