[PATCH v6 net-next 1/1] tcp: Replace min_tso_segs() with tso_segs() CC callback

@@ -824,6 +824,9 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
 unsigned int tcp_current_mss(struct sock *sk);
 u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when);
 
+u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
+		     int min_tso_segs);
+
 /* Bound MSS / TSO packet size with the half of the window */
 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
 {

@@ -1361,8 +1364,13 @@ struct tcp_congestion_ops {
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
 
-	/* override sysctl_tcp_min_tso_segs (optional) */
-	u32 (*min_tso_segs)(struct sock *sk);
+	/* Override tcp_tso_autosize (optional)
+	 *
+	 * If provided, this callback returns the final TSO segment number
+	 * and will bypass tcp_tso_autosize() entirely. The implementation
+	 * must derive an appropriate value and ensure the result is valid.
+	 */
+	u32 (*tso_segs)(struct sock *sk, u32 mss_now);
 
 	/* new value of cwnd after loss (required) */
 	u32  (*undo_cwnd)(struct sock *sk);

@@ -284,9 +284,12 @@ static void bpf_tcp_ca_pkts_acked(struct sock *sk, const struct ack_sample *samp
 {
 }
 
-static u32 bpf_tcp_ca_min_tso_segs(struct sock *sk)
+static u32 bpf_tcp_ca_tso_segs(struct sock *sk, u32 mss_now)
 {
-	return 0;
+	if (unlikely(!mss_now))
+		/* No TSO sizing decision. Let caller apply its limits. */
+		return U32_MAX;
+	return tcp_tso_autosize(sk, mss_now, 0);
 }
 
 static void bpf_tcp_ca_cong_control(struct sock *sk, u32 ack, int flag,

@@ -320,7 +323,7 @@ static struct tcp_congestion_ops __bpf_ops_tcp_congestion_ops = {
 	.cwnd_event_tx_start = bpf_tcp_ca_cwnd_event_tx_start,
 	.in_ack_event = bpf_tcp_ca_in_ack_event,
 	.pkts_acked = bpf_tcp_ca_pkts_acked,
-	.min_tso_segs = bpf_tcp_ca_min_tso_segs,
+	.tso_segs = bpf_tcp_ca_tso_segs,
 	.cong_control = bpf_tcp_ca_cong_control,
 	.undo_cwnd = bpf_tcp_ca_undo_cwnd,
 	.sndbuf_expand = bpf_tcp_ca_sndbuf_expand,

@@ -297,11 +297,18 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
 }
 
 /* override sysctl_tcp_min_tso_segs */
-__bpf_kfunc static u32 bbr_min_tso_segs(struct sock *sk)
+static u32 bbr_min_tso_segs(struct sock *sk)
 {
 	return READ_ONCE(sk->sk_pacing_rate) < (bbr_min_tso_rate >> 3) ? 1 : 2;
 }
 
+__bpf_kfunc static u32 bbr_tso_segs(struct sock *sk, u32 mss_now)
+{
+	if (unlikely(!mss_now))
+		return bbr_min_tso_segs(sk);
+	return tcp_tso_autosize(sk, mss_now, bbr_min_tso_segs(sk));
+}
+
 static u32 bbr_tso_segs_goal(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);

@@ -1151,7 +1158,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
 	.undo_cwnd	= bbr_undo_cwnd,
 	.cwnd_event_tx_start	= bbr_cwnd_event_tx_start,
 	.ssthresh	= bbr_ssthresh,
-	.min_tso_segs	= bbr_min_tso_segs,
+	.tso_segs	= bbr_tso_segs,
 	.get_info	= bbr_get_info,
 	.set_state	= bbr_set_state,
 };

@@ -1163,7 +1170,7 @@ BTF_ID_FLAGS(func, bbr_sndbuf_expand)
 BTF_ID_FLAGS(func, bbr_undo_cwnd)
 BTF_ID_FLAGS(func, bbr_cwnd_event_tx_start)
 BTF_ID_FLAGS(func, bbr_ssthresh)
-BTF_ID_FLAGS(func, bbr_min_tso_segs)
+BTF_ID_FLAGS(func, bbr_tso_segs)
 BTF_ID_FLAGS(func, bbr_set_state)
 BTF_KFUNCS_END(tcp_bbr_check_kfunc_ids)
 

@@ -2253,8 +2253,8 @@ static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
  * for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance
  * is below 1500 bytes after 6 * ~500 usec = 3ms.
  */
-static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
-			    int min_tso_segs)
+u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
+		     int min_tso_segs)
 {
 	unsigned long bytes;
 	u32 r;

@@ -2269,6 +2269,7 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
 
 	return max_t(u32, bytes / mss_now, min_tso_segs);
 }
+EXPORT_SYMBOL(tcp_tso_autosize);
 
 /* Return the number of segments we want in the skb we are transmitting.
  * See if congestion control module wants to decide; otherwise, autosize.

@@ -2278,12 +2279,12 @@ static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
 	u32 min_tso, tso_segs;
 
-	min_tso = ca_ops->min_tso_segs ?
-			ca_ops->min_tso_segs(sk) :
-			READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
+	min_tso = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
 
-	tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
-	return min_t(u32, tso_segs, sk->sk_gso_max_segs);
+	tso_segs = ca_ops->tso_segs ?
+			ca_ops->tso_segs(sk, mss_now) :
+			tcp_tso_autosize(sk, mss_now, min_tso);
+	return clamp_t(u32, tso_segs, 1, sk->sk_gso_max_segs);
 }
 
 /* Returns the portion of skb which can be sent right away */

@@ -10,7 +10,7 @@ extern u32 bbr_sndbuf_expand(struct sock *sk) __ksym;
 extern u32 bbr_undo_cwnd(struct sock *sk) __ksym;
 extern void bbr_cwnd_event_tx_start(struct sock *sk) __ksym;
 extern u32 bbr_ssthresh(struct sock *sk) __ksym;
-extern u32 bbr_min_tso_segs(struct sock *sk) __ksym;
+extern u32 bbr_tso_segs(struct sock *sk, u32 mss_now) __ksym;
 extern void bbr_set_state(struct sock *sk, u8 new_state) __ksym;
 
 extern void dctcp_init(struct sock *sk) __ksym;

@@ -90,9 +90,9 @@ u32 BPF_PROG(ssthresh, struct sock *sk)
 }
 
 SEC("struct_ops")
-u32 BPF_PROG(min_tso_segs, struct sock *sk)
+u32 BPF_PROG(tso_segs, struct sock *sk, u32 mss_now)
 {
-	return bbr_min_tso_segs(sk);
+	return bbr_tso_segs(sk, mss_now);
 }
 
 SEC("struct_ops")

@@ -120,7 +120,7 @@ struct tcp_congestion_ops tcp_ca_kfunc = {
 	.cwnd_event	= (void *)cwnd_event,
 	.cwnd_event_tx_start = (void *)cwnd_event_tx_start,
 	.ssthresh	= (void *)ssthresh,
-	.min_tso_segs	= (void *)min_tso_segs,
+	.tso_segs	= (void *)tso_segs,
 	.set_state	= (void *)set_state,
 	.pkts_acked     = (void *)pkts_acked,
 	.name		= "tcp_ca_kfunc",