bonding: 3ad: add lacp_strict configuration knob

When an 802.3ad (LACP) bonding interface has no slaves in the
collecting/distributing state, the bonding master still reports
carrier as up as long as at least 'min_links' slaves have carrier.

In this situation, only one slave is effectively used for TX/RX,
while traffic received on other slaves is dropped. Upper-layer
daemons therefore consider the interface operational, even though
traffic may be blackholed if the lack of LACP negotiation means
the partner is not ready to deal with traffic.

Introduce a configuration knob to control this behavior. It allows
the bonding master to assert carrier only when at least 'min_links'
slaves are in Collecting_Distributing state.

The default mode preserves the existing behavior. This patch only
introduces the knob; its behavior is implemented in the subsequent
commit.

Fixes: 655f891 ("bonding: add min links parameter to 802.3ad")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>
Acked-by: Jay Vosburgh <jv@jvosburgh.net>
Link: https://patch.msgid.link/20260603150331.1919611-4-louis.scalbert@6wind.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: louis-6wind

Documentation/netlink/specs/rt-link.yaml

@@ -1356,6 +1356,9 @@ attribute-sets:
       -
         name: broadcast-neigh
         type: u8
+      -
+        name: lacp-strict
+        type: u8
   -
     name: bond-ad-info-attrs
     name-prefix: ifla-bond-ad-info-

Documentation/networking/bonding.rst

@@ -619,6 +619,29 @@ min_links
 	aggregator cannot be active without at least one available link,
 	setting this option to 0 or to 1 has the exact same effect.
 
+lacp_strict
+
+	Specifies the fallback behavior of a bonding when LACP negotiation
+	fails on all slave links, i.e. when no slave is in the
+	Collecting_Distributing state, while at least `min_links` link still
+	reports carrier up.
+
+	This option is only applicable to 802.3ad mode (mode 4).
+
+	Valid values are:
+
+	off or 0
+		One interface of the bond is selected to be active, in order to
+		facilitate communication with peer devices that do not implement
+		LACP.
+
+	on or 1
+		Interfaces are only permitted to be made active if they have an
+		active LACP partner and have successfully reached
+		Collecting_Distributing state.
+
+	The default value is 0 (off).
+
 mode
 
 	Specifies one of the bonding policies. The default is

drivers/net/bonding/bond_main.c

@@ -6457,6 +6457,7 @@ static int __init bond_check_params(struct bond_params *params)
 	params->ad_user_port_key = ad_user_port_key;
 	params->coupled_control = 1;
 	params->broadcast_neighbor = 0;
+	params->lacp_strict = 0;
 	if (packets_per_slave > 0) {
 		params->reciprocal_packets_per_slave =
 			reciprocal_value(packets_per_slave);

drivers/net/bonding/bond_netlink.c

@@ -143,6 +143,7 @@ static const struct nla_policy bond_policy[IFLA_BOND_MAX + 1] = {
 	[IFLA_BOND_NS_IP6_TARGET]	= { .type = NLA_NESTED },
 	[IFLA_BOND_COUPLED_CONTROL]	= { .type = NLA_U8 },
 	[IFLA_BOND_BROADCAST_NEIGH]	= { .type = NLA_U8 },
+	[IFLA_BOND_LACP_STRICT]		= { .type = NLA_U8 },
 };
 
 static const struct nla_policy bond_slave_policy[IFLA_BOND_SLAVE_MAX + 1] = {
@@ -599,6 +600,16 @@ static int bond_changelink(struct net_device *bond_dev, struct nlattr *tb[],
 			return err;
 	}
 
+	if (data[IFLA_BOND_LACP_STRICT]) {
+		int fallback_mode = nla_get_u8(data[IFLA_BOND_LACP_STRICT]);
+
+		bond_opt_initval(&newval, fallback_mode);
+		err = __bond_opt_set(bond, BOND_OPT_LACP_STRICT, &newval,
+				     data[IFLA_BOND_LACP_STRICT], extack);
+		if (err)
+			return err;
+	}
+
 	return 0;
 }
 
@@ -671,6 +682,7 @@ static size_t bond_get_size(const struct net_device *bond_dev)
 		nla_total_size(sizeof(struct in6_addr)) * BOND_MAX_NS_TARGETS +
 		nla_total_size(sizeof(u8)) +	/* IFLA_BOND_COUPLED_CONTROL */
 		nla_total_size(sizeof(u8)) +	/* IFLA_BOND_BROADCAST_NEIGH */
+		nla_total_size(sizeof(u8)) +	/* IFLA_BOND_LACP_STRICT */
 		0;
 }
 
@@ -838,6 +850,10 @@ static int bond_fill_info(struct sk_buff *skb,
 		       bond->params.broadcast_neighbor))
 		goto nla_put_failure;
 
+	if (nla_put_u8(skb, IFLA_BOND_LACP_STRICT,
+		       bond->params.lacp_strict))
+		goto nla_put_failure;
+
 	if (BOND_MODE(bond) == BOND_MODE_8023AD) {
 		struct ad_info info;
 

drivers/net/bonding/bond_options.c

@@ -68,6 +68,8 @@ static int bond_option_lacp_active_set(struct bonding *bond,
 				       const struct bond_opt_value *newval);
 static int bond_option_lacp_rate_set(struct bonding *bond,
 				     const struct bond_opt_value *newval);
+static int bond_option_lacp_strict_set(struct bonding *bond,
+				       const struct bond_opt_value *newval);
 static int bond_option_ad_select_set(struct bonding *bond,
 				     const struct bond_opt_value *newval);
 static int bond_option_queue_id_set(struct bonding *bond,
@@ -162,6 +164,12 @@ static const struct bond_opt_value bond_lacp_rate_tbl[] = {
 	{ NULL,   -1,           0},
 };
 
+static const struct bond_opt_value bond_lacp_strict_tbl[] = {
+	{ "off", 0, BOND_VALFLAG_DEFAULT},
+	{ "on",  1, 0},
+	{ NULL, -1, 0 }
+};
+
 static const struct bond_opt_value bond_ad_select_tbl[] = {
 	{ "stable",          BOND_AD_STABLE,    BOND_VALFLAG_DEFAULT},
 	{ "bandwidth",       BOND_AD_BANDWIDTH, 0},
@@ -363,6 +371,14 @@ static const struct bond_option bond_opts[BOND_OPT_LAST] = {
 		.values = bond_lacp_rate_tbl,
 		.set = bond_option_lacp_rate_set
 	},
+	[BOND_OPT_LACP_STRICT] = {
+		.id = BOND_OPT_LACP_STRICT,
+		.name = "lacp_strict",
+		.desc = "Define the LACP fallback mode when no slaves have negotiated",
+		.unsuppmodes = BOND_MODE_ALL_EX(BIT(BOND_MODE_8023AD)),
+		.values = bond_lacp_strict_tbl,
+		.set = bond_option_lacp_strict_set
+	},
 	[BOND_OPT_MINLINKS] = {
 		.id = BOND_OPT_MINLINKS,
 		.name = "min_links",
@@ -1685,6 +1701,16 @@ static int bond_option_lacp_rate_set(struct bonding *bond,
 	return 0;
 }
 
+static int bond_option_lacp_strict_set(struct bonding *bond,
+				       const struct bond_opt_value *newval)
+{
+	netdev_dbg(bond->dev, "Setting LACP fallback to %s (%llu)\n",
+		   newval->string, newval->value);
+	bond->params.lacp_strict = newval->value;
+
+	return 0;
+}
+
 static int bond_option_ad_select_set(struct bonding *bond,
 				     const struct bond_opt_value *newval)
 {

include/net/bond_options.h

@@ -79,6 +79,7 @@ enum {
 	BOND_OPT_COUPLED_CONTROL,
 	BOND_OPT_BROADCAST_NEIGH,
 	BOND_OPT_ACTOR_PORT_PRIO,
+	BOND_OPT_LACP_STRICT,
 	BOND_OPT_LAST
 };
 

include/net/bonding.h

@@ -129,6 +129,7 @@ struct bond_params {
 	int peer_notif_delay;
 	int lacp_active;
 	int lacp_fast;
+	int lacp_strict;
 	unsigned int min_links;
 	int ad_select;
 	char primary[IFNAMSIZ];

include/uapi/linux/if_link.h

@@ -1603,6 +1603,7 @@ enum {
 	IFLA_BOND_NS_IP6_TARGET,
 	IFLA_BOND_COUPLED_CONTROL,
 	IFLA_BOND_BROADCAST_NEIGH,
+	IFLA_BOND_LACP_STRICT,
 	__IFLA_BOND_MAX,
 };
 

tools/include/uapi/linux/if_link.h

@@ -1527,6 +1527,7 @@ enum {
 	IFLA_BOND_NS_IP6_TARGET,
 	IFLA_BOND_COUPLED_CONTROL,
 	IFLA_BOND_BROADCAST_NEIGH,
+	IFLA_BOND_LACP_STRICT,
 	__IFLA_BOND_MAX,
 };