[PATCH net v3 1/5] bonding: 3ad: add lacp_fallback configuration knob

[Louis Scalbert <louis.scalbert@6wind.com>]

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 (or collecting only
when coupled_control is disabled).

The default mode preserves the current (legacy) behavior. This
patch only introduces the knob; its behavior is implemented in
the subsequent commit.

Fixes: 655f8919d549 ("bonding: add min links parameter to 802.3ad")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>
---
 Documentation/networking/bonding.rst | 33 ++++++++++++++++++++++++++++
 drivers/net/bonding/bond_main.c      |  1 +
 drivers/net/bonding/bond_netlink.c   | 16 ++++++++++++++
 drivers/net/bonding/bond_options.c   | 26 ++++++++++++++++++++++
 include/net/bond_options.h           |  1 +
 include/net/bonding.h                |  1 +
 include/uapi/linux/if_link.h         |  1 +
 7 files changed, 79 insertions(+)

diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
index e700bf1d095c..465d06aead27 100644
--- a/Documentation/networking/bonding.rst
+++ b/Documentation/networking/bonding.rst
@@ -619,6 +619,39 @@ 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_fallback
+
+	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
+	(or only in Collecting state when coupled_control is disabled), while at
+	least `min_links` link still reports carrier up.
+
+	This option is only applicable to 802.3ad mode (mode 4).
+
+	Valid values are:
+
+	legacy or 0
+		In this situation, the bonding master remains carrier up and
+		randomly selects a single slave to transmit and receive traffic.
+		Traffic received on other slaves is dropped.
+
+		This mode is deprecated, as it may lead to traffic blackholing
+		when the absence of LACP negotiation means the partner is not
+		ready to collect and distribute traffic.
+
+		This is the legacy default behavior.
+
+	strict or 1
+		In this situation, the bonding master reports carrier down, allowing
+		upper-layer processes to detect that the interface is not usable for
+		collecting and distributing traffic.
+
+		The master transitions to carrier up only when at least
+		`min_links` slaves reach the Collecting(/Distributing) state,
+		allowing traffic to flow.
+
+	The default value is 0 (legacy).
+
 mode
 
 	Specifies one of the bonding policies. The default is
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index a5484d11553d..02cba0560a39 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -6440,6 +6440,7 @@ 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_fallback = 0;
 	if (packets_per_slave > 0) {
 		params->reciprocal_packets_per_slave =
 			reciprocal_value(packets_per_slave);
diff --git a/drivers/net/bonding/bond_netlink.c b/drivers/net/bonding/bond_netlink.c
index 286f11c517f7..1f92ad786b51 100644
--- a/drivers/net/bonding/bond_netlink.c
+++ b/drivers/net/bonding/bond_netlink.c
@@ -130,6 +130,7 @@ 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_FALLBACK]	= { .type = NLA_U8 },
 };
 
 static const struct nla_policy bond_slave_policy[IFLA_BOND_SLAVE_MAX + 1] = {
@@ -586,6 +587,16 @@ static int bond_changelink(struct net_device *bond_dev, struct nlattr *tb[],
 			return err;
 	}
 
+	if (data[IFLA_BOND_LACP_FALLBACK]) {
+		int fallback_mode = nla_get_u8(data[IFLA_BOND_LACP_FALLBACK]);
+
+		bond_opt_initval(&newval, fallback_mode);
+		err = __bond_opt_set(bond, BOND_OPT_LACP_FALLBACK, &newval,
+				     data[IFLA_BOND_LACP_FALLBACK], extack);
+		if (err)
+			return err;
+	}
+
 	return 0;
 }
 
@@ -658,6 +669,7 @@ 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_FALLBACK */
 		0;
 }
 
@@ -825,6 +837,10 @@ 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_FALLBACK,
+		       bond->params.lacp_fallback))
+		goto nla_put_failure;
+
 	if (BOND_MODE(bond) == BOND_MODE_8023AD) {
 		struct ad_info info;
 
diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
index 7380cc4ee75a..b672b8a881bb 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/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_fallback_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_fallback_tbl[] = {
+	{ "legacy", 0, BOND_VALFLAG_DEFAULT},
+	{ "strict",  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_FALLBACK] = {
+		.id = BOND_OPT_LACP_FALLBACK,
+		.name = "lacp_fallback",
+		.desc = "Define the LACP fallback mode when no slaves have negotiated",
+		.unsuppmodes = BOND_MODE_ALL_EX(BIT(BOND_MODE_8023AD)),
+		.values = bond_lacp_fallback_tbl,
+		.set = bond_option_lacp_fallback_set
+	},
 	[BOND_OPT_MINLINKS] = {
 		.id = BOND_OPT_MINLINKS,
 		.name = "min_links",
@@ -1684,6 +1700,16 @@ static int bond_option_lacp_rate_set(struct bonding *bond,
 	return 0;
 }
 
+static int bond_option_lacp_fallback_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_fallback = newval->value;
+
+	return 0;
+}
+
 static int bond_option_ad_select_set(struct bonding *bond,
 				     const struct bond_opt_value *newval)
 {
diff --git a/include/net/bond_options.h b/include/net/bond_options.h
index e6eedf23aea1..5eb64c831f54 100644
--- a/include/net/bond_options.h
+++ b/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_FALLBACK,
 	BOND_OPT_LAST
 };
 
diff --git a/include/net/bonding.h b/include/net/bonding.h
index 395c6e281c5f..d8cb02643f8b 100644
--- a/include/net/bonding.h
+++ b/include/net/bonding.h
@@ -132,6 +132,7 @@ struct bond_params {
 	int peer_notif_delay;
 	int lacp_active;
 	int lacp_fast;
+	int lacp_fallback;
 	unsigned int min_links;
 	int ad_select;
 	char primary[IFNAMSIZ];
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index e9b5f79e1ee1..7ad3fc600c71 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -1539,6 +1539,7 @@ enum {
 	IFLA_BOND_NS_IP6_TARGET,
 	IFLA_BOND_COUPLED_CONTROL,
 	IFLA_BOND_BROADCAST_NEIGH,
+	IFLA_BOND_LACP_FALLBACK,
 	__IFLA_BOND_MAX,
 };
 
-- 
2.39.2