bonding: make speed, duplex setting consistent with link state

bond_update_speed_duplex() retrieves speed and duplex settings. There
is a possibility of failure in retrieving these values but caller has
to assume it's always successful. This leads to having inconsistent
slave link settings. If these (speed, duplex) values cannot be
retrieved, then keeping the link UP causes problems.

The updated bond_update_speed_duplex() returns 0 on success if it
retrieves sane values for speed and duplex. On failure it returns 1
and marks the link down.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -365,9 +365,10 @@ down:
 /* Get link speed and duplex from the slave's base driver
  * using ethtool. If for some reason the call fails or the
  * values are invalid, set speed and duplex to -1,
- * and return.
+ * and return. Return 1 if speed or duplex settings are
+ * UNKNOWN; 0 otherwise.
  */
-static void bond_update_speed_duplex(struct slave *slave)
+static int bond_update_speed_duplex(struct slave *slave)
 {
 	struct net_device *slave_dev = slave->dev;
 	struct ethtool_link_ksettings ecmd;
@@ -377,24 +378,27 @@ static void bond_update_speed_duplex(struct slave *slave)
 	slave->duplex = DUPLEX_UNKNOWN;
 
 	res = __ethtool_get_link_ksettings(slave_dev, &ecmd);
-	if (res < 0)
-		return;
-
-	if (ecmd.base.speed == 0 || ecmd.base.speed == ((__u32)-1))
-		return;
-
+	if (res < 0) {
+		slave->link = BOND_LINK_DOWN;
+		return 1;
+	}
+	if (ecmd.base.speed == 0 || ecmd.base.speed == ((__u32)-1)) {
+		slave->link = BOND_LINK_DOWN;
+		return 1;
+	}
 	switch (ecmd.base.duplex) {
 	case DUPLEX_FULL:
 	case DUPLEX_HALF:
 		break;
 	default:
-		return;
+		slave->link = BOND_LINK_DOWN;
+		return 1;
 	}
 
 	slave->speed = ecmd.base.speed;
 	slave->duplex = ecmd.base.duplex;
 
-	return;
+	return 0;
 }
 
 const char *bond_slave_link_status(s8 link)