MINOR: protocol: add a pair of check_events/ignore_events functions at the ctrl layer

Right now the connection subscribe/unsubscribe code needs to manipulate
FDs, which is not compatible with QUIC. In practice what we need there
is to be able to either subscribe or wake up depending on readiness at
the moment of subscription.

This commit introduces two new functions at the control layer, which are
provided by the socket code, to check for FD readiness or subscribe to it
at the control layer. For now it's not used.

include/haproxy/protocol-t.h

@@ -100,6 +100,8 @@ struct protocol {
 	void (*ctrl_close)(struct connection *);        /* completes release of the connection */
 	int (*connect)(struct connection *, int flags); /* connect function if any, see below for flags values */
 	int (*drain)(struct connection *);              /* drain pending data; 0=failed, >0=success */
+	int (*check_events)(struct connection *conn, int event_type);  /* subscribe to socket events */
+	void (*ignore_events)(struct connection *conn, int event_type);  /* unsubscribe from socket events */
 
 	/* functions acting on the receiver */
 	int (*rx_suspend)(struct receiver *rx);         /* temporarily suspend this receiver for a soft restart */

include/haproxy/sock.h

@@ -48,6 +48,8 @@ void sock_conn_ctrl_close(struct connection *conn);
 void sock_conn_iocb(int fd);
 int sock_conn_check(struct connection *conn);
 int sock_drain(struct connection *conn);
+int sock_check_events(struct connection *conn, int event_type);
+void sock_ignore_events(struct connection *conn, int event_type);
 
 
 #endif /* _HAPROXY_SOCK_H */

src/proto_sockpair.c

@@ -78,6 +78,8 @@ struct protocol proto_sockpair = {
 	.ctrl_close     = sock_conn_ctrl_close,
 	.connect        = sockpair_connect_server,
 	.drain          = sock_drain,
+	.check_events   = sock_check_events,
+	.ignore_events  = sock_ignore_events,
 
 	/* binding layer */
 	/* Note: suspend/resume not supported */

src/proto_tcp.c

@@ -68,6 +68,8 @@ struct protocol proto_tcpv4 = {
 	.ctrl_close     = sock_conn_ctrl_close,
 	.connect        = tcp_connect_server,
 	.drain          = sock_drain,
+	.check_events   = sock_check_events,
+	.ignore_events  = sock_ignore_events,
 
 	/* binding layer */
 	.rx_suspend     = tcp_suspend_receiver,
@@ -108,6 +110,8 @@ struct protocol proto_tcpv6 = {
 	.ctrl_close     = sock_conn_ctrl_close,
 	.connect        = tcp_connect_server,
 	.drain          = sock_drain,
+	.check_events   = sock_check_events,
+	.ignore_events  = sock_ignore_events,
 
 	/* binding layer */
 	.rx_suspend     = tcp_suspend_receiver,

src/proto_uxst.c

@@ -64,6 +64,8 @@ struct protocol proto_uxst = {
 	.ctrl_close     = sock_conn_ctrl_close,
 	.connect        = uxst_connect_server,
 	.drain          = sock_drain,
+	.check_events   = sock_check_events,
+	.ignore_events  = sock_ignore_events,
 
 	/* binding layer */
 	.rx_suspend     = uxst_suspend_receiver,

src/sock.c

@@ -872,6 +872,45 @@ int sock_drain(struct connection *conn)
 	return 1;
 }
 
+/* Checks the connection's FD for readiness of events <event_type>, which may
+ * only be a combination of SUB_RETRY_RECV and SUB_RETRY_SEND. Those which are
+ * ready are returned. The ones that are not ready are enabled. The caller is
+ * expected to do what is needed to handle ready events and to deal with
+ * subsequent wakeups caused by the requested events' readiness.
+ */
+int sock_check_events(struct connection *conn, int event_type)
+{
+	int ret = 0;
+
+	if (event_type & SUB_RETRY_RECV) {
+		if (fd_recv_ready(conn->handle.fd))
+			ret |= SUB_RETRY_RECV;
+		else
+			fd_want_recv(conn->handle.fd);
+	}
+
+	if (event_type & SUB_RETRY_SEND) {
+		if (fd_send_ready(conn->handle.fd))
+			ret |= SUB_RETRY_SEND;
+		else
+			fd_want_send(conn->handle.fd);
+	}
+
+	return ret;
+}
+
+/* Ignore readiness events from connection's FD for events of types <event_type>
+ * which may only be a combination of SUB_RETRY_RECV and SUB_RETRY_SEND.
+ */
+void sock_ignore_events(struct connection *conn, int event_type)
+{
+	if (event_type & SUB_RETRY_RECV)
+		fd_stop_recv(conn->handle.fd);
+
+	if (event_type & SUB_RETRY_SEND)
+		fd_stop_send(conn->handle.fd);
+}
+
 /*
  * Local variables:
  *  c-indent-level: 8