ipv4: implement igmp_qrv sysctl to tune igmp robustness variable

As in IPv6 people might increase the igmp query robustness variable to
make sure unsolicited state change reports aren't lost on the network. Add
and document this new knob to igmp code.

RFCs allow tuning this parameter back to first IGMP RFC, so we also use
this setting for all counters, including source specific multicast.

Also take over sysctl value when upping the interface and don't reuse
the last one seen on the interface.

Cc: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -844,6 +844,11 @@ igmp_max_memberships - INTEGER
 
 	conf/all/*	  is special, changes the settings for all interfaces
 
+igmp_qrv - INTEGER
+	 Controls the IGMP query robustness variable (see RFC2236 8.1).
+	 Default: 2 (as specified by RFC2236 8.1)
+	 Minimum: 1 (as specified by RFC6636 4.5)
+
 log_martians - BOOLEAN
 	Log packets with impossible addresses to kernel log.
 	log_martians for the interface will be enabled if at least one of

include/linux/igmp.h

@@ -39,6 +39,7 @@ static inline struct igmpv3_query *
 
 extern int sysctl_igmp_max_memberships;
 extern int sysctl_igmp_max_msf;
+extern int sysctl_igmp_qrv;
 
 struct ip_sf_socklist {
 	unsigned int		sl_max;

net/ipv4/igmp.c

@@ -117,7 +117,7 @@
 #define IGMP_V2_Unsolicited_Report_Interval	(10*HZ)
 #define IGMP_V3_Unsolicited_Report_Interval	(1*HZ)
 #define IGMP_Query_Response_Interval		(10*HZ)
-#define IGMP_Unsolicited_Report_Count		2
+#define IGMP_Query_Robustness_Variable		2
 
 
 #define IGMP_Initial_Report_Delay		(1)
@@ -756,8 +756,7 @@ static void igmp_ifc_event(struct in_device *in_dev)
 {
 	if (IGMP_V1_SEEN(in_dev) || IGMP_V2_SEEN(in_dev))
 		return;
-	in_dev->mr_ifc_count = in_dev->mr_qrv ? in_dev->mr_qrv :
-		IGMP_Unsolicited_Report_Count;
+	in_dev->mr_ifc_count = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 	igmp_ifc_start_timer(in_dev, 1);
 }
 
@@ -1086,8 +1085,7 @@ static void igmpv3_add_delrec(struct in_device *in_dev, struct ip_mc_list *im)
 	pmc->interface = im->interface;
 	in_dev_hold(in_dev);
 	pmc->multiaddr = im->multiaddr;
-	pmc->crcount = in_dev->mr_qrv ? in_dev->mr_qrv :
-		IGMP_Unsolicited_Report_Count;
+	pmc->crcount = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 	pmc->sfmode = im->sfmode;
 	if (pmc->sfmode == MCAST_INCLUDE) {
 		struct ip_sf_list *psf;
@@ -1226,8 +1224,7 @@ static void igmp_group_added(struct ip_mc_list *im)
 	}
 	/* else, v3 */
 
-	im->crcount = in_dev->mr_qrv ? in_dev->mr_qrv :
-		IGMP_Unsolicited_Report_Count;
+	im->crcount = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 	igmp_ifc_event(in_dev);
 #endif
 }
@@ -1322,7 +1319,7 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 addr)
 	spin_lock_init(&im->lock);
 #ifdef CONFIG_IP_MULTICAST
 	setup_timer(&im->timer, igmp_timer_expire, (unsigned long)im);
-	im->unsolicit_count = IGMP_Unsolicited_Report_Count;
+	im->unsolicit_count = sysctl_igmp_qrv;
 #endif
 
 	im->next_rcu = in_dev->mc_list;
@@ -1460,7 +1457,7 @@ void ip_mc_init_dev(struct in_device *in_dev)
 			(unsigned long)in_dev);
 	setup_timer(&in_dev->mr_ifc_timer, igmp_ifc_timer_expire,
 			(unsigned long)in_dev);
-	in_dev->mr_qrv = IGMP_Unsolicited_Report_Count;
+	in_dev->mr_qrv = sysctl_igmp_qrv;
 #endif
 
 	spin_lock_init(&in_dev->mc_tomb_lock);
@@ -1474,6 +1471,9 @@ void ip_mc_up(struct in_device *in_dev)
 
 	ASSERT_RTNL();
 
+#ifdef CONFIG_IP_MULTICAST
+	in_dev->mr_qrv = sysctl_igmp_qrv;
+#endif
 	ip_mc_inc_group(in_dev, IGMP_ALL_HOSTS);
 
 	for_each_pmc_rtnl(in_dev, pmc)
@@ -1540,7 +1540,9 @@ static struct in_device *ip_mc_find_dev(struct net *net, struct ip_mreqn *imr)
  */
 int sysctl_igmp_max_memberships __read_mostly = IP_MAX_MEMBERSHIPS;
 int sysctl_igmp_max_msf __read_mostly = IP_MAX_MSF;
-
+#ifdef CONFIG_IP_MULTICAST
+int sysctl_igmp_qrv __read_mostly = IGMP_Query_Robustness_Variable;
+#endif
 
 static int ip_mc_del1_src(struct ip_mc_list *pmc, int sfmode,
 	__be32 *psfsrc)
@@ -1575,8 +1577,7 @@ static int ip_mc_del1_src(struct ip_mc_list *pmc, int sfmode,
 #ifdef CONFIG_IP_MULTICAST
 		if (psf->sf_oldin &&
 		    !IGMP_V1_SEEN(in_dev) && !IGMP_V2_SEEN(in_dev)) {
-			psf->sf_crcount = in_dev->mr_qrv ? in_dev->mr_qrv :
-				IGMP_Unsolicited_Report_Count;
+			psf->sf_crcount = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 			psf->sf_next = pmc->tomb;
 			pmc->tomb = psf;
 			rv = 1;
@@ -1639,8 +1640,7 @@ static int ip_mc_del_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
 		/* filter mode change */
 		pmc->sfmode = MCAST_INCLUDE;
 #ifdef CONFIG_IP_MULTICAST
-		pmc->crcount = in_dev->mr_qrv ? in_dev->mr_qrv :
-			IGMP_Unsolicited_Report_Count;
+		pmc->crcount = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 		in_dev->mr_ifc_count = pmc->crcount;
 		for (psf = pmc->sources; psf; psf = psf->sf_next)
 			psf->sf_crcount = 0;
@@ -1818,8 +1818,7 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
 #ifdef CONFIG_IP_MULTICAST
 		/* else no filters; keep old mode for reports */
 
-		pmc->crcount = in_dev->mr_qrv ? in_dev->mr_qrv :
-			IGMP_Unsolicited_Report_Count;
+		pmc->crcount = in_dev->mr_qrv ?: sysctl_igmp_qrv;
 		in_dev->mr_ifc_count = pmc->crcount;
 		for (psf = pmc->sources; psf; psf = psf->sf_next)
 			psf->sf_crcount = 0;

net/ipv4/sysctl_net_ipv4.c

@@ -450,6 +450,16 @@ static struct ctl_table ipv4_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+#ifdef CONFIG_IP_MULTICAST
+	{
+		.procname	= "igmp_qrv",
+		.data		= &sysctl_igmp_qrv,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &one
+	},
+#endif
 	{
 		.procname	= "inet_peer_threshold",
 		.data		= &inet_peer_threshold,