rtnetlink: RTEXT_FILTER_SKIP_STATS support to avoid dumping inet/inet6 stats

Many commonly used functions like getifaddrs() invoke RTM_GETLINK
to dump the interface information, and do not need the
the AF_INET6 statististics that are always returned by default
from rtnl_fill_ifinfo().

Computing the statistics can be an expensive operation that impacts
scaling, so it is desirable to avoid this if the information is
not needed.

This patch adds a the RTEXT_FILTER_SKIP_STATS extended info flag that
can be passed with netlink_request() to avoid statistics computation
for the ifinfo path.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 030fefd..75d3dde 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4729,7 +4729,8 @@
 	}
 }
 
-static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev)
+static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev,
+				  u32 ext_filter_mask)
 {
 	struct nlattr *nla;
 	struct ifla_cacheinfo ci;
@@ -4749,6 +4750,9 @@
 
 	/* XXX - MC not implemented */
 
+	if (ext_filter_mask & RTEXT_FILTER_SKIP_STATS)
+		return 0;
+
 	nla = nla_reserve(skb, IFLA_INET6_STATS, IPSTATS_MIB_MAX * sizeof(u64));
 	if (!nla)
 		goto nla_put_failure;
@@ -4784,14 +4788,15 @@
 	return inet6_ifla6_size();
 }
 
-static int inet6_fill_link_af(struct sk_buff *skb, const struct net_device *dev)
+static int inet6_fill_link_af(struct sk_buff *skb, const struct net_device *dev,
+			      u32 ext_filter_mask)
 {
 	struct inet6_dev *idev = __in6_dev_get(dev);
 
 	if (!idev)
 		return -ENODATA;
 
-	if (inet6_fill_ifla6_attrs(skb, idev) < 0)
+	if (inet6_fill_ifla6_attrs(skb, idev, ext_filter_mask) < 0)
 		return -EMSGSIZE;
 
 	return 0;
@@ -4946,7 +4951,7 @@
 	if (!protoinfo)
 		goto nla_put_failure;
 
-	if (inet6_fill_ifla6_attrs(skb, idev) < 0)
+	if (inet6_fill_ifla6_attrs(skb, idev, 0) < 0)
 		goto nla_put_failure;
 
 	nla_nest_end(skb, protoinfo);