MINOR: quic/pacing: support pacing emission on quic_conn layer

Pacing will be implemented for STREAM frames emission. As such,
qc_send_mux() API has been extended to add an argument to a quic_pacer
engine.

If non NULL, engine will be used to pace emission. In short, no more
than one datagram will be emitted for each qc_send_mux() invokation.
Pacer is then notified about the emission and a timer for a future
emission is calculated. qc_send_mux() will return AGAIN value and QUIC
MUX will then be responsible to retry emission when the timer is
reached.

Author: a-denoyelle

include/haproxy/quic_pacing.h

@@ -17,6 +17,9 @@ static inline void quic_pacing_init(struct quic_pacer *pacer,
 
 int quic_pacing_expired(const struct quic_pacer *pacer);
 
+
 void quic_pacing_sent_done(struct quic_pacer *pacer);
 
+enum quic_tx_err quic_pacing_send(struct quic_pacer *pacer, struct quic_conn *qc);
+
 #endif /* _HAPROXY_QUIC_PACING_H */

include/haproxy/quic_tx-t.h

@@ -66,6 +66,7 @@ enum qc_build_pkt_err {
 
 enum quic_tx_err {
 	QUIC_TX_ERR_NONE,
+	QUIC_TX_ERR_AGAIN,
 	QUIC_TX_ERR_FATAL,
 };
 

include/haproxy/quic_tx.h

@@ -25,6 +25,7 @@
 #include <haproxy/list-t.h>
 #include <haproxy/quic_conn-t.h>
 #include <haproxy/quic_tls-t.h>
+#include <haproxy/quic_pacing-t.h>
 #include <haproxy/quic_rx-t.h>
 #include <haproxy/quic_tx-t.h>
 
@@ -33,7 +34,8 @@ void qc_txb_release(struct quic_conn *qc);
 int qc_purge_txbuf(struct quic_conn *qc, struct buffer *buf);
 struct buffer *qc_get_txb(struct quic_conn *qc);
 
-enum quic_tx_err qc_send_mux(struct quic_conn *qc, struct list *frms);
+enum quic_tx_err qc_send_mux(struct quic_conn *qc, struct list *frms,
+                             struct quic_pacer *pacer);
 
 void qel_register_send(struct list *send_list, struct quic_enc_level *qel,
                        struct list *frms);

src/mux_quic.c

@@ -2091,7 +2091,7 @@ static int qcc_send_frames(struct qcc *qcc, struct list *frms)
 		return 1;
 	}
 
-	ret = qc_send_mux(qcc->conn->handle.qc, frms);
+	ret = qc_send_mux(qcc->conn->handle.qc, frms, NULL);
 	if (ret == QUIC_TX_ERR_FATAL) {
 		TRACE_DEVEL("error on sending", QMUX_EV_QCC_SEND, qcc->conn);
 		qcc_subscribe_send(qcc);

src/quic_pacing.c

@@ -13,3 +13,16 @@ void quic_pacing_sent_done(struct quic_pacer *pacer)
 {
 	pacer->next = now_mono_time() + pacer->cc->algo->pacing_rate(pacer->cc);
 }
+
+/* Restart emission after <pacer> has delayed some frames on <qc> connection.
+ *
+ * Returns the value of qc_send_mux() call.
+ */
+enum quic_tx_err quic_pacing_send(struct quic_pacer *pacer, struct quic_conn *qc)
+{
+	if (!quic_pacing_expired(pacer))
+		return QUIC_TX_ERR_AGAIN;
+
+	BUG_ON(LIST_ISEMPTY(pacer->frms));
+	return qc_send_mux(qc, pacer->frms, pacer);
+}

src/quic_tx.c

@@ -20,6 +20,7 @@
 #include <haproxy/trace.h>
 #include <haproxy/quic_cid.h>
 #include <haproxy/quic_conn.h>
+#include <haproxy/quic_pacing.h>
 #include <haproxy/quic_retransmit.h>
 #include <haproxy/quic_retry.h>
 #include <haproxy/quic_sock.h>
@@ -469,11 +470,12 @@ int qc_purge_txbuf(struct quic_conn *qc, struct buffer *buf)
  *
  * Returns the result from qc_send() function.
  */
-enum quic_tx_err qc_send_mux(struct quic_conn *qc, struct list *frms)
+enum quic_tx_err qc_send_mux(struct quic_conn *qc, struct list *frms,
+                             struct quic_pacer *pacer)
 {
 	struct list send_list = LIST_HEAD_INIT(send_list);
 	enum quic_tx_err ret = QUIC_TX_ERR_NONE;
-	int sent;
+	int max_dgram = 0, sent;
 
 	TRACE_ENTER(QUIC_EV_CONN_TXPKT, qc);
 	BUG_ON(qc->mux_state != QC_MUX_READY); /* Only MUX can uses this function so it must be ready. */
@@ -492,11 +494,21 @@ enum quic_tx_err qc_send_mux(struct quic_conn *qc, struct list *frms)
 		qc_send(qc, 0, &send_list, 0);
 	}
 
+	if (pacer)
+		max_dgram = 1;
+
 	TRACE_STATE("preparing data (from MUX)", QUIC_EV_CONN_TXPKT, qc);
 	qel_register_send(&send_list, qc->ael, frms);
-	sent = qc_send(qc, 0, &send_list, 0);
-	if (sent <= 0)
+	sent = qc_send(qc, 0, &send_list, max_dgram);
+	if (sent <= 0) {
 		ret = QUIC_TX_ERR_FATAL;
+	}
+	else if (pacer) {
+		BUG_ON(sent > 1); /* burst not yet supported for pacing */
+		if (!LIST_ISEMPTY(frms))
+			ret = QUIC_TX_ERR_AGAIN;
+		quic_pacing_sent_done(pacer);
+	}
 
 	TRACE_LEAVE(QUIC_EV_CONN_TXPKT, qc);
 	return ret;