[PATCH mptcp-next] net: skip printing "link become ready" v6 msg

[Matthieu Baerts <matthieu.baerts@tessares.net>]

This following message is printed in the console each time a network
device configured with an IPv6 addresses is ready to be used:

  ADDRCONF(NETDEV_CHANGE): <iface>: link becomes ready

When netns are being extensively used, e.g. by re-creating netns with
veth to discuss with each other for testing purposes like mptcp_join.sh
selftest is doing, it generates a lot of messages: more than 700 with
the latest version.

This message can be useful in many situations but in some, it floods the
logs without providing any useful input. The proposition here is to have
a new sysctl knob to easily skip this specific message.

Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
 include/net/netns/ipv6.h                        | 1 +
 net/ipv6/addrconf.c                             | 5 +++--
 net/ipv6/sysctl_net_ipv6.c                      | 9 +++++++++
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 1 +
 4 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 3cceb3e9320b..721abf86052f 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -56,6 +56,7 @@ struct netns_sysctl_ipv6 {
 	bool skip_notify_on_dev_down;
 	u8 fib_notify_on_flag_change;
 	u8 icmpv6_error_anycast_as_unicast;
+	bool skip_print_link_becomes_ready;
 };
 
 struct netns_ipv6 {
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3797917237d0..9cf7b4932309 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3633,8 +3633,9 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 				idev->if_flags |= IF_READY;
 			}
 
-			pr_info("ADDRCONF(NETDEV_CHANGE): %s: link becomes ready\n",
-				dev->name);
+			if (!net->ipv6.sysctl.skip_print_link_becomes_ready)
+				pr_info("ADDRCONF(NETDEV_CHANGE): %s: link becomes ready\n",
+					dev->name);
 
 			run_pending = 1;
 		}
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 94a0a294c6a1..c9e82377a8fa 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -213,6 +213,15 @@ static struct ctl_table ipv6_table_template[] = {
 		.proc_handler	= proc_doulongvec_minmax,
 		.extra2		= &ioam6_id_wide_max,
 	},
+	{
+		.procname	= "skip_print_link_becomes_ready",
+		.data		= &init_net.ipv6.sysctl.skip_print_link_becomes_ready,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
 	{ }
 };
 
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 0044d87556dd..27179e9175be 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -84,6 +84,7 @@ init_partial()
 		ip netns exec $netns sysctl -q net.mptcp.pm_type=0
 		ip netns exec $netns sysctl -q net.ipv4.conf.all.rp_filter=0
 		ip netns exec $netns sysctl -q net.ipv4.conf.default.rp_filter=0
+		ip netns exec $netns sysctl -q net.ipv6.skip_print_link_becomes_ready=1 2>/dev/null || true
 		if [ $checksum -eq 1 ]; then
 			ip netns exec $netns sysctl -q net.mptcp.checksum_enabled=1
 		fi

---
base-commit: 194dd0efe579cb5d3a746d248b3476f4b3fc0b48
change-id: 20230522-mptcp-skip_print_link_becomes_ready-af50c71a9daa

Best regards,
-- 
Matthieu Baerts <matthieu.baerts@tessares.net>