[PATCH net-next] bonding: show master index when dumping slave info

[Hangbin Liu <liuhangbin@gmail.com>]

Currently, there is no straightforward way to obtain the master/slave
relationship via netlink. Users have to retrieve all slaves through sysfs
to determine these relationships.

To address this, we can either list all slaves under the bond interface
or display the master index in each slave. Since the number of slaves could
be quite large (e.g., 100+), it is more efficient to show the master
information in the slave entry.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
---
 drivers/net/bonding/bond_netlink.c | 4 ++++
 include/uapi/linux/if_link.h       | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/net/bonding/bond_netlink.c b/drivers/net/bonding/bond_netlink.c
index 286f11c517f7..ff3f11674a8b 100644
--- a/drivers/net/bonding/bond_netlink.c
+++ b/drivers/net/bonding/bond_netlink.c
@@ -29,6 +29,7 @@ static size_t bond_get_slave_size(const struct net_device *bond_dev,
 		nla_total_size(sizeof(u16)) +	/* IFLA_BOND_SLAVE_AD_PARTNER_OPER_PORT_STATE */
 		nla_total_size(sizeof(s32)) +	/* IFLA_BOND_SLAVE_PRIO */
 		nla_total_size(sizeof(u16)) +	/* IFLA_BOND_SLAVE_ACTOR_PORT_PRIO */
+		nla_total_size(sizeof(u32)) +	/* IFLA_BOND_SLAVE_MASTER */
 		0;
 }
 
@@ -38,6 +39,9 @@ static int bond_fill_slave_info(struct sk_buff *skb,
 {
 	struct slave *slave = bond_slave_get_rtnl(slave_dev);
 
+	if (nla_put_u32(skb, IFLA_BOND_SLAVE_MASTER, bond_dev->ifindex))
+		goto nla_put_failure;
+
 	if (nla_put_u8(skb, IFLA_BOND_SLAVE_STATE, bond_slave_state(slave)))
 		goto nla_put_failure;
 
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 3b491d96e52e..bad41a1807f7 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -1567,6 +1567,7 @@ enum {
 	IFLA_BOND_SLAVE_AD_PARTNER_OPER_PORT_STATE,
 	IFLA_BOND_SLAVE_PRIO,
 	IFLA_BOND_SLAVE_ACTOR_PORT_PRIO,
+	IFLA_BOND_SLAVE_MASTER,
 	__IFLA_BOND_SLAVE_MAX,
 };
 
-- 
2.50.1