MINOR: backend: refactor insertion in avail conns tree

Define a new function srv_add_to_avail_list(). This function is used to
centralize connection insertion in available tree. It reuses a BUG_ON()
statement to ensure the connection is not present in the idle list.

include/haproxy/server.h

@@ -87,6 +87,7 @@ struct connection *srv_lookup_conn_next(struct connection *conn);
 
 void _srv_add_idle(struct server *srv, struct connection *conn, int is_safe);
 int srv_add_to_idle_list(struct server *srv, struct connection *conn, int is_safe);
+void srv_add_to_avail_list(struct server *srv, struct connection *conn);
 struct task *srv_cleanup_toremove_conns(struct task *task, void *context, unsigned int state);
 
 int srv_apply_track(struct server *srv, struct proxy *curproxy);

src/backend.c

@@ -1276,8 +1276,7 @@ static struct connection *conn_backend_get(struct stream *s, struct server *srv,
 			session_add_conn(s->sess, conn, conn->target);
 		}
 		else {
-			eb64_insert(&srv->per_thr[tid].avail_conns,
-			            &conn->hash_node->node);
+			srv_add_to_avail_list(srv, conn);
 		}
 	}
 	return conn;
@@ -1781,7 +1780,7 @@ static int connect_server(struct stream *s)
 			if (srv && reuse_mode == PR_O_REUSE_ALWS &&
 			    !(srv_conn->flags & CO_FL_PRIVATE) &&
 			    srv_conn->mux->avail_streams(srv_conn) > 0) {
-				eb64_insert(&srv->per_thr[tid].avail_conns, &srv_conn->hash_node->node);
+				srv_add_to_avail_list(srv, srv_conn);
 			}
 			else if (srv_conn->flags & CO_FL_PRIVATE ||
 			         (reuse_mode == PR_O_REUSE_SAFE &&

src/connection.c

@@ -29,6 +29,7 @@
 #include <haproxy/proto_tcp.h>
 #include <haproxy/sample.h>
 #include <haproxy/sc_strm.h>
+#include <haproxy/server.h>
 #include <haproxy/session.h>
 #include <haproxy/ssl_sock.h>
 #include <haproxy/stconn.h>
@@ -107,8 +108,9 @@ int conn_create_mux(struct connection *conn)
 		 * server list.
 		 */
 		if (srv && ((srv->proxy->options & PR_O_REUSE_MASK) == PR_O_REUSE_ALWS) &&
-		    !(conn->flags & CO_FL_PRIVATE) && conn->mux->avail_streams(conn) > 0)
-			eb64_insert(&srv->per_thr[tid].avail_conns, &conn->hash_node->node);
+		    !(conn->flags & CO_FL_PRIVATE) && conn->mux->avail_streams(conn) > 0) {
+			srv_add_to_avail_list(srv, conn);
+		}
 		else if (conn->flags & CO_FL_PRIVATE) {
 			/* If it fail now, the same will be done in mux->detach() callback */
 			session_add_conn(sess, conn, conn->target);

src/mux_fcgi.c

@@ -32,6 +32,7 @@
 #include <haproxy/proxy.h>
 #include <haproxy/regex.h>
 #include <haproxy/sc_strm.h>
+#include <haproxy/server.h>
 #include <haproxy/session-t.h>
 #include <haproxy/stconn.h>
 #include <haproxy/stream.h>
@@ -3603,8 +3604,7 @@ static void fcgi_detach(struct sedesc *sd)
 			else if (!fconn->conn->hash_node->node.node.leaf_p &&
 				 fcgi_avail_streams(fconn->conn) > 0 && objt_server(fconn->conn->target) &&
 				 !LIST_INLIST(&fconn->conn->session_list)) {
-				eb64_insert(&__objt_server(fconn->conn->target)->per_thr[tid].avail_conns,
-				            &fconn->conn->hash_node->node);
+				srv_add_to_avail_list(__objt_server(fconn->conn->target), fconn->conn);
 			}
 		}
 	}

src/mux_h2.c

@@ -27,6 +27,7 @@
 #include <haproxy/mux_h2-t.h>
 #include <haproxy/net_helper.h>
 #include <haproxy/proxy.h>
+#include <haproxy/server.h>
 #include <haproxy/session-t.h>
 #include <haproxy/stats.h>
 #include <haproxy/stconn.h>
@@ -4651,8 +4652,7 @@ static void h2_detach(struct sedesc *sd)
 				else if (!h2c->conn->hash_node->node.node.leaf_p &&
 					 h2_avail_streams(h2c->conn) > 0 && objt_server(h2c->conn->target) &&
 					 !LIST_INLIST(&h2c->conn->session_list)) {
-					eb64_insert(&__objt_server(h2c->conn->target)->per_thr[tid].avail_conns,
-					            &h2c->conn->hash_node->node);
+					srv_add_to_avail_list(__objt_server(h2c->conn->target), h2c->conn);
 				}
 			}
 		}

src/server.c

@@ -6136,6 +6136,16 @@ int srv_add_to_idle_list(struct server *srv, struct connection *conn, int is_saf
 	return 0;
 }
 
+/* Insert <conn> connection in <srv> server available list. This is reserved
+ * for backend connection currently in used with usable streams left.
+ */
+void srv_add_to_avail_list(struct server *srv, struct connection *conn)
+{
+	/* connection cannot be in idle list if used as an avail idle conn. */
+	BUG_ON(LIST_INLIST(&conn->idle_list));
+	eb64_insert(&srv->per_thr[tid].avail_conns, &conn->hash_node->node);
+}
+
 struct task *srv_cleanup_idle_conns(struct task *task, void *context, unsigned int state)
 {
 	struct server *srv;