ethtool: add tunnel info interface

Add an interface to report offloaded UDP ports via ethtool netlink.

Now that core takes care of tracking which UDP tunnel ports the NICs
are aware of we can quite easily export this information out to
user space.

The responsibility of writing the netlink dumps is split between
ethtool code and udp_tunnel_nic.c - since udp_tunnel module may
not always be loaded, yet we should always report the capabilities
of the NIC.

$ ethtool --show-tunnels eth0
Tunnel information for eth0:
  UDP port table 0:
    Size: 4
    Types: vxlan
    No entries
  UDP port table 1:
    Size: 4
    Types: geneve, vxlan-gpe
    Entries (1):
        port 1230, vxlan-gpe

v4:
 - back to v2, build fix is now directly in udp_tunnel.h
v3:
 - don't compile ETHTOOL_MSG_TUNNEL_INFO_GET in if CONFIG_INET
   not set.
v2:
 - fix string set count,
 - reorder enums in the uAPI,
 - fix type of ETHTOOL_A_TUNNEL_UDP_TABLE_TYPES to bitset
   in docs and comments.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp_tunnel_nic.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 // Copyright (c) 2020 Facebook Inc.
 
+#include <linux/ethtool_netlink.h>
 #include <linux/netdevice.h>
 #include <linux/slab.h>
 #include <linux/types.h>
@@ -72,6 +73,12 @@ udp_tunnel_nic_entry_is_free(struct udp_tunnel_nic_table_entry *entry)
 	return entry->use_cnt == 0 && !entry->flags;
 }
 
+static bool
+udp_tunnel_nic_entry_is_present(struct udp_tunnel_nic_table_entry *entry)
+{
+	return entry->use_cnt && !(entry->flags & ~UDP_TUNNEL_NIC_ENTRY_FROZEN);
+}
+
 static bool
 udp_tunnel_nic_entry_is_frozen(struct udp_tunnel_nic_table_entry *entry)
 {
@@ -564,12 +571,74 @@ static void __udp_tunnel_nic_reset_ntf(struct net_device *dev)
 	__udp_tunnel_nic_device_sync(dev, utn);
 }
 
+static size_t
+__udp_tunnel_nic_dump_size(struct net_device *dev, unsigned int table)
+{
+	const struct udp_tunnel_nic_info *info = dev->udp_tunnel_nic_info;
+	struct udp_tunnel_nic *utn;
+	unsigned int j;
+	size_t size;
+
+	utn = dev->udp_tunnel_nic;
+	if (!utn)
+		return 0;
+
+	size = 0;
+	for (j = 0; j < info->tables[table].n_entries; j++) {
+		if (!udp_tunnel_nic_entry_is_present(&utn->entries[table][j]))
+			continue;
+
+		size += nla_total_size(0) +		 /* _TABLE_ENTRY */
+			nla_total_size(sizeof(__be16)) + /* _ENTRY_PORT */
+			nla_total_size(sizeof(u32));	 /* _ENTRY_TYPE */
+	}
+
+	return size;
+}
+
+static int
+__udp_tunnel_nic_dump_write(struct net_device *dev, unsigned int table,
+			    struct sk_buff *skb)
+{
+	const struct udp_tunnel_nic_info *info = dev->udp_tunnel_nic_info;
+	struct udp_tunnel_nic *utn;
+	struct nlattr *nest;
+	unsigned int j;
+
+	utn = dev->udp_tunnel_nic;
+	if (!utn)
+		return 0;
+
+	for (j = 0; j < info->tables[table].n_entries; j++) {
+		if (!udp_tunnel_nic_entry_is_present(&utn->entries[table][j]))
+			continue;
+
+		nest = nla_nest_start(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_ENTRY);
+
+		if (nla_put_be16(skb, ETHTOOL_A_TUNNEL_UDP_ENTRY_PORT,
+				 utn->entries[table][j].port) ||
+		    nla_put_u32(skb, ETHTOOL_A_TUNNEL_UDP_ENTRY_TYPE,
+				ilog2(utn->entries[table][j].type)))
+			goto err_cancel;
+
+		nla_nest_end(skb, nest);
+	}
+
+	return 0;
+
+err_cancel:
+	nla_nest_cancel(skb, nest);
+	return -EMSGSIZE;
+}
+
 static const struct udp_tunnel_nic_ops __udp_tunnel_nic_ops = {
 	.get_port	= __udp_tunnel_nic_get_port,
 	.set_port_priv	= __udp_tunnel_nic_set_port_priv,
 	.add_port	= __udp_tunnel_nic_add_port,
 	.del_port	= __udp_tunnel_nic_del_port,
 	.reset_ntf	= __udp_tunnel_nic_reset_ntf,
+	.dump_size	= __udp_tunnel_nic_dump_size,
+	.dump_write	= __udp_tunnel_nic_dump_write,
 };
 
 static void