net: report min and max mtu network device settings

Report the minimum and maximum MTU allowed on a device
via netlink so that it can be displayed by tools like
ip link.
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/uapi/linux/if_link.h

@@ -164,6 +164,8 @@ enum {
 	IFLA_CARRIER_UP_COUNT,
 	IFLA_CARRIER_DOWN_COUNT,
 	IFLA_NEW_IFINDEX,
+	IFLA_MIN_MTU,
+	IFLA_MAX_MTU,
 	__IFLA_MAX
 };
 

net/core/rtnetlink.c

@@ -1015,6 +1015,8 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
 	       + nla_total_size(4)  /* IFLA_IF_NETNSID */
 	       + nla_total_size(4)  /* IFLA_CARRIER_UP_COUNT */
 	       + nla_total_size(4)  /* IFLA_CARRIER_DOWN_COUNT */
+	       + nla_total_size(4)  /* IFLA_MIN_MTU */
+	       + nla_total_size(4)  /* IFLA_MAX_MTU */
 	       + 0;
 }
 
@@ -1601,6 +1603,8 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 		       netif_running(dev) ? dev->operstate : IF_OPER_DOWN) ||
 	    nla_put_u8(skb, IFLA_LINKMODE, dev->link_mode) ||
 	    nla_put_u32(skb, IFLA_MTU, dev->mtu) ||
+	    nla_put_u32(skb, IFLA_MIN_MTU, dev->min_mtu) ||
+	    nla_put_u32(skb, IFLA_MAX_MTU, dev->max_mtu) ||
 	    nla_put_u32(skb, IFLA_GROUP, dev->group) ||
 	    nla_put_u32(skb, IFLA_PROMISCUITY, dev->promiscuity) ||
 	    nla_put_u32(skb, IFLA_NUM_TX_QUEUES, dev->num_tx_queues) ||
@@ -1732,6 +1736,8 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
 	[IFLA_IF_NETNSID]	= { .type = NLA_S32 },
 	[IFLA_CARRIER_UP_COUNT]	= { .type = NLA_U32 },
 	[IFLA_CARRIER_DOWN_COUNT] = { .type = NLA_U32 },
+	[IFLA_MIN_MTU]		= { .type = NLA_U32 },
+	[IFLA_MAX_MTU]		= { .type = NLA_U32 },
 };
 
 static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {