net: dsa: allow the DSA master to be seen and changed through rtnetlink

Some DSA switches have multiple CPU ports, which can be used to improve
CPU termination throughput, but DSA, through dsa_tree_setup_cpu_ports(),
sets up only the first one, leading to suboptimal use of hardware.

The desire is to not change the default configuration but to permit the
user to create a dynamic mapping between individual user ports and the
CPU port that they are served by, configurable through rtnetlink. It is
also intended to permit load balancing between CPU ports, and in that
case, the foreseen model is for the DSA master to be a bonding interface
whose lowers are the physical DSA masters.

To that end, we create a struct rtnl_link_ops for DSA user ports with
the "dsa" kind. We expose the IFLA_DSA_MASTER link attribute that
contains the ifindex of the newly desired DSA master.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/net/dsa/netlink.c b/net/dsa/netlink.c
new file mode 100644
index 000000000000..0f43bbb94769
--- /dev/null
+++ b/net/dsa/netlink.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright 2022 NXP
+ */
+#include <linux/netdevice.h>
+#include <net/rtnetlink.h>
+
+#include "dsa_priv.h"
+
+static const struct nla_policy dsa_policy[IFLA_DSA_MAX + 1] = {
+	[IFLA_DSA_MASTER]	= { .type = NLA_U32 },
+};
+
+static int dsa_changelink(struct net_device *dev, struct nlattr *tb[],
+			  struct nlattr *data[],
+			  struct netlink_ext_ack *extack)
+{
+	int err;
+
+	if (!data)
+		return 0;
+
+	if (data[IFLA_DSA_MASTER]) {
+		u32 ifindex = nla_get_u32(data[IFLA_DSA_MASTER]);
+		struct net_device *master;
+
+		master = __dev_get_by_index(dev_net(dev), ifindex);
+		if (!master)
+			return -EINVAL;
+
+		err = dsa_slave_change_master(dev, master, extack);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static size_t dsa_get_size(const struct net_device *dev)
+{
+	return nla_total_size(sizeof(u32)) +	/* IFLA_DSA_MASTER  */
+	       0;
+}
+
+static int dsa_fill_info(struct sk_buff *skb, const struct net_device *dev)
+{
+	struct net_device *master = dsa_slave_to_master(dev);
+
+	if (nla_put_u32(skb, IFLA_DSA_MASTER, master->ifindex))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+struct rtnl_link_ops dsa_link_ops __read_mostly = {
+	.kind			= "dsa",
+	.priv_size		= sizeof(struct dsa_port),
+	.maxtype		= IFLA_DSA_MAX,
+	.policy			= dsa_policy,
+	.changelink		= dsa_changelink,
+	.get_size		= dsa_get_size,
+	.fill_info		= dsa_fill_info,
+};