IO: Replace RX priority heuristic with explicit mark

In BIRD, RX has lower priority than TX with the exception of RX from
control socket. The patch replaces heuristic based on socket type with
explicit mark and uses it for both control socket and BGP session waiting
to be established.

This should avoid an issue when during heavy load, outgoing connection
could connect (TX event), send open, but then failed to receive OPEN /
establish in time, not sending notifications between and therefore
got hold timer expired error from the neighbor immediately after it
finally established the connection.

lib/socket.h

@@ -28,6 +28,7 @@ typedef struct birdsock {
   struct iface *iface;			/* Interface; specify this for broad/multicast sockets */
 
   byte *rbuf, *rpos;			/* NULL=allocate automatically */
+  uint fast_rx;				/* RX has higher priority in event loop */
   uint rbsize;
   int (*rx_hook)(struct birdsock *, int size); /* NULL=receiving turned off, returns 1 to clear rx buffer */
 

proto/bgp/bgp.c

@@ -374,6 +374,8 @@ bgp_conn_enter_established_state(struct bgp_conn *conn)
   if (ipa_zero(p->source_addr))
     p->source_addr = conn->sk->saddr;
 
+  conn->sk->fast_rx = 0;
+
   p->conn = conn;
   p->last_error_class = 0;
   p->last_error_code = 0;
@@ -696,6 +698,7 @@ bgp_setup_sk(struct bgp_conn *conn, sock *s)
 {
   s->data = conn;
   s->err_hook = bgp_sock_err;
+  s->fast_rx = 1;
   conn->sk = s;
 }
 

sysdep/unix/io.c

@@ -2152,7 +2152,7 @@ io_loop(void)
 	      int steps;
 
 	      steps = MAX_STEPS;
-	      if ((s->type >= SK_MAGIC) && (pfd[s->index].revents & (POLLIN | POLLHUP | POLLERR)) && s->rx_hook)
+	      if (s->fast_rx && (pfd[s->index].revents & (POLLIN | POLLHUP | POLLERR)) && s->rx_hook)
 		do
 		  {
 		    steps--;
@@ -2197,7 +2197,7 @@ io_loop(void)
 		  goto next2;
 		}
 
-	      if ((s->type < SK_MAGIC) && (pfd[s->index].revents & (POLLIN | POLLHUP | POLLERR)) && s->rx_hook)
+	      if (!s->fast_rx && (pfd[s->index].revents & (POLLIN | POLLHUP | POLLERR)) && s->rx_hook)
 		{
 		  count++;
 		  io_log_event(s->rx_hook, s->data);

sysdep/unix/main.c

@@ -450,6 +450,7 @@ cli_connect(sock *s, int size UNUSED)
   s->err_hook = cli_err;
   s->data = c = cli_new(s);
   s->pool = c->pool;		/* We need to have all the socket buffers allocated in the cli pool */
+  s->fast_rx = 1;
   c->rx_pos = c->rx_buf;
   c->rx_aux = NULL;
   rmove(s, c->pool);
@@ -466,6 +467,7 @@ cli_init_unix(uid_t use_uid, gid_t use_gid)
   s->type = SK_UNIX_PASSIVE;
   s->rx_hook = cli_connect;
   s->rbsize = 1024;
+  s->fast_rx = 1;
 
   /* Return value intentionally ignored */
   unlink(path_control_socket);