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>

include/net/tcp.h

@@ -804,6 +804,8 @@ enum tcp_ca_ack_event_flags {
 /* 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 @@ struct tcp_congestion_ops {
 	/* 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;

include/uapi/linux/inet_diag.h

@@ -143,4 +143,8 @@ struct tcp_dctcp_info {
 	__u32	dctcp_ab_tot;
 };
 
+union tcp_cc_info {
+	struct tcpvegas_info	vegas;
+	struct tcp_dctcp_info	dctcp;
+};
 #endif /* _UAPI_INET_DIAG_H_ */

net/ipv4/inet_diag.c

@@ -224,14 +224,16 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 	handler->idiag_get_info(sk, r, info);
 
 	if (sk->sk_state < TCP_TIME_WAIT) {
-		int err = 0;
+		union tcp_cc_info info;
+		size_t sz = 0;
+		int attr;
 
 		rcu_read_lock();
 		ca_ops = READ_ONCE(icsk->icsk_ca_ops);
 		if (ca_ops && ca_ops->get_info)
-			err = ca_ops->get_info(sk, ext, skb);
+			sz = ca_ops->get_info(sk, ext, &attr, &info);
 		rcu_read_unlock();
-		if (err < 0)
+		if (sz && nla_put(skb, attr, sz, &info) < 0)
 			goto errout;
 	}
 

net/ipv4/tcp_dctcp.c

@@ -277,7 +277,8 @@ static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
 	}
 }
 
-static int dctcp_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
+static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
+			     union tcp_cc_info *info)
 {
 	const struct dctcp *ca = inet_csk_ca(sk);
 
@@ -286,18 +287,17 @@ static int dctcp_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
 	 */
 	if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
 	    ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
-		struct tcp_dctcp_info info;
-
-		memset(&info, 0, sizeof(info));
+		memset(info, 0, sizeof(struct tcp_dctcp_info));
 		if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
-			info.dctcp_enabled = 1;
-			info.dctcp_ce_state = (u16) ca->ce_state;
-			info.dctcp_alpha = ca->dctcp_alpha;
-			info.dctcp_ab_ecn = ca->acked_bytes_ecn;
-			info.dctcp_ab_tot = ca->acked_bytes_total;
+			info->dctcp.dctcp_enabled = 1;
+			info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
+			info->dctcp.dctcp_alpha = ca->dctcp_alpha;
+			info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn;
+			info->dctcp.dctcp_ab_tot = ca->acked_bytes_total;
 		}
 
-		return nla_put(skb, INET_DIAG_DCTCPINFO, sizeof(info), &info);
+		*attr = INET_DIAG_DCTCPINFO;
+		return sizeof(*info);
 	}
 	return 0;
 }

net/ipv4/tcp_illinois.c

@@ -300,24 +300,25 @@ static u32 tcp_illinois_ssthresh(struct sock *sk)
 }
 
 /* Extract info for Tcp socket info provided via netlink. */
-static int tcp_illinois_info(struct sock *sk, u32 ext, struct sk_buff *skb)
+static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
+				union tcp_cc_info *info)
 {
 	const struct illinois *ca = inet_csk_ca(sk);
 
 	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
-		struct tcpvegas_info info = {
-			.tcpv_enabled = 1,
-			.tcpv_rttcnt = ca->cnt_rtt,
-			.tcpv_minrtt = ca->base_rtt,
-		};
+		info->vegas.tcpv_enabled = 1;
+		info->vegas.tcpv_rttcnt = ca->cnt_rtt;
+		info->vegas.tcpv_minrtt = ca->base_rtt;
+		info->vegas.tcpv_rtt = 0;
 
-		if (info.tcpv_rttcnt > 0) {
+		if (info->vegas.tcpv_rttcnt > 0) {
 			u64 t = ca->sum_rtt;
 
-			do_div(t, info.tcpv_rttcnt);
-			info.tcpv_rtt = t;
+			do_div(t, info->vegas.tcpv_rttcnt);
+			info->vegas.tcpv_rtt = t;
 		}
-		return nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
+		*attr = INET_DIAG_VEGASINFO;
+		return sizeof(struct tcpvegas_info);
 	}
 	return 0;
 }

net/ipv4/tcp_vegas.c

@@ -286,18 +286,19 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 }
 
 /* Extract info for Tcp socket info provided via netlink. */
-int tcp_vegas_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
+size_t tcp_vegas_get_info(struct sock *sk, u32 ext, int *attr,
+			  union tcp_cc_info *info)
 {
 	const struct vegas *ca = inet_csk_ca(sk);
+
 	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
-		struct tcpvegas_info info = {
-			.tcpv_enabled = ca->doing_vegas_now,
-			.tcpv_rttcnt = ca->cntRTT,
-			.tcpv_rtt = ca->baseRTT,
-			.tcpv_minrtt = ca->minRTT,
-		};
-
-		return nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
+		info->vegas.tcpv_enabled = ca->doing_vegas_now,
+		info->vegas.tcpv_rttcnt = ca->cntRTT,
+		info->vegas.tcpv_rtt = ca->baseRTT,
+		info->vegas.tcpv_minrtt = ca->minRTT,
+
+		*attr = INET_DIAG_VEGASINFO;
+		return sizeof(struct tcpvegas_info);
 	}
 	return 0;
 }

net/ipv4/tcp_vegas.h

@@ -19,6 +19,7 @@ void tcp_vegas_init(struct sock *sk);
 void tcp_vegas_state(struct sock *sk, u8 ca_state);
 void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us);
 void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event);
-int tcp_vegas_get_info(struct sock *sk, u32 ext, struct sk_buff *skb);
+size_t tcp_vegas_get_info(struct sock *sk, u32 ext, int *attr,
+			  union tcp_cc_info *info);
 
 #endif	/* __TCP_VEGAS_H */