Backport of commit 73318c5b99571c8da01474ad665e2e2e06ab12bb
Author: Richard Cochran <richardcochran@gmail.com>
Date:   Sun Feb 5 18:31:27 2017 +0100

    clock: Force a BMC election when a port link goes down.
    
    Having one fewer port may affect the result of the BMCA.  This patch
    changes the main loop so that a link down event also causes a state
    decision event.
    
    Signed-off-by: Richard Cochran <richardcochran@gmail.com>
    Reported-by: Henry Jesuiter <Henry.Jesuiter@alcnetworx.de>

diff -up linuxptp-1.8/clock.c.linkdown linuxptp-1.8/clock.c
--- linuxptp-1.8/clock.c.linkdown	2017-03-15 08:37:03.017542152 +0100
+++ linuxptp-1.8/clock.c	2017-03-15 08:42:53.238682318 +0100
@@ -96,6 +96,7 @@ struct clock {
 	int pollfd_valid;
 	int nports; /* does not include the UDS port */
 	int last_port_number;
+	int sde;
 	struct hash *index2port;
 	int free_running;
 	int freq_est_interval;
@@ -341,6 +342,11 @@ static void clock_link_status(void *ctx,
 		port_dispatch(p, EV_FAULT_CLEARED, 0);
 	} else {
 		port_dispatch(p, EV_FAULT_DETECTED, 0);
+		/*
+		 * A port going down can affect the BMCA result.
+		 * Force a state decision event.
+		 */
+		c->sde = 1;
 	}
 }
 
@@ -1465,7 +1471,7 @@ struct PortIdentity clock_parent_identit
 
 int clock_poll(struct clock *c)
 {
-	int cnt, err, i, sde = 0;
+	int cnt, err, i;
 	enum fsm_event event;
 	struct pollfd *cur;
 	struct port *p;
@@ -1496,9 +1502,9 @@ int clock_poll(struct clock *c)
 			if (cur[i].revents & (POLLIN|POLLPRI)) {
 				event = port_event(p, i);
 				if (EV_STATE_DECISION_EVENT == event)
-					sde = 1;
+					c->sde = 1;
 				if (EV_ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES == event)
-					sde = 1;
+					c->sde = 1;
 				err = port_dispatch(p, event, 0);
 				/* Clear any fault after a little while. */
 				if (PS_FAULTY == port_state(p)) {
@@ -1527,13 +1533,14 @@ int clock_poll(struct clock *c)
 		if (cur[i].revents & (POLLIN|POLLPRI)) {
 			event = port_event(c->uds_port, i);
 			if (EV_STATE_DECISION_EVENT == event)
-				sde = 1;
+				c->sde = 1;
 		}
 	}
 
-	if (sde)
+	if (c->sde) {
 		handle_state_decision_event(c);
-
+		c->sde = 0;
+	}
 	clock_prune_subscriptions(c);
 	return 0;
 }