bonding: documentation and code cleanup for resend_igmp

Improves the documentation about how IGMP resend parameter
works, fix two missing checks and coding style issues.
Signed-off-by: Flavio Leitner <fbl@redhat.com>
Acked-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/bonding.txt

@@ -770,8 +770,17 @@ resend_igmp
 	a failover event. One membership report is issued immediately after
 	the failover, subsequent packets are sent in each 200ms interval.
 
-	The valid range is 0 - 255; the default value is 1. This option
-	was added for bonding version 3.7.0.
+	The valid range is 0 - 255; the default value is 1. A value of 0
+	prevents the IGMP membership report from being issued in response
+	to the failover event.
+
+	This option is useful for bonding modes balance-rr (0), active-backup
+	(1), balance-tlb (5) and balance-alb (6), in which a failover can
+	switch the IGMP traffic from one slave to another.  Therefore a fresh
+	IGMP report must be issued to cause the switch to forward the incoming
+	IGMP traffic over the newly selected slave.
+
+	This option was added for bonding version 3.7.0.
 
 3. Configuring Bonding Devices
 ==============================

drivers/net/bonding/bond_main.c

@@ -1172,10 +1172,12 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active)
 	}
 
 	/* resend IGMP joins since active slave has changed or
-	 * all were sent on curr_active_slave */
-	if (((USES_PRIMARY(bond->params.mode) && new_active) ||
-	     bond->params.mode == BOND_MODE_ROUNDROBIN) &&
-	    netif_running(bond->dev)) {
+	 * all were sent on curr_active_slave.
+	 * resend only if bond is brought up with the affected
+	 * bonding modes and the retransmission is enabled */
+	if (netif_running(bond->dev) && (bond->params.resend_igmp > 0) &&
+	    ((USES_PRIMARY(bond->params.mode) && new_active) ||
+	     bond->params.mode == BOND_MODE_ROUNDROBIN)) {
 		bond->igmp_retrans = bond->params.resend_igmp;
 		queue_delayed_work(bond->wq, &bond->mcast_work, 0);
 	}

drivers/net/bonding/bond_sysfs.c

@@ -1555,7 +1555,7 @@ static ssize_t bonding_store_resend_igmp(struct device *d,
 		goto out;
 	}
 
-	if (new_value < 0) {
+	if (new_value < 0 || new_value > 255) {
 		pr_err("%s: Invalid resend_igmp value %d not in range 0-255; rejected.\n",
 		       bond->dev->name, new_value);
 		ret = -EINVAL;