rtnetlink: honor RTEXT_FILTER_SKIP_STATS in IFLA_STATS

Gathering interface statistics can be a relatively expensive operation
on certain systems as it requires iterating over all the cpus.

RTEXT_FILTER_SKIP_STATS was first introduced [1] to skip AF_INET6
statistics from interface dumps and it was then extended [2] to
also exclude IFLA_VF_INFO.

The semantics of the flag does not seem to be limited to AF_INET
or VF statistics and having a way to query the interface status
(e.g: carrier, address) without retrieving its statistics seems
reasonable. So this patch extends the use RTEXT_FILTER_SKIP_STATS
to also affect IFLA_STATS.

[1] https://lore.kernel.org/all/[e-mail]/
[2] https://lore.kernel.org/all/[e-mail]/

Signed-off-by: Adrian Moreno <[e-mail]>
Reviewed-by: Toke Høiland-Jørgensen <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Reviewed-by: Nicolas Dichtel <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/core/rtnetlink.c

···
 static noinline size_t if_nlmsg_size(const struct net_device *dev,
 				     u32 ext_filter_mask)
 {
-	return NLMSG_ALIGN(sizeof(struct ifinfomsg))
+	size_t size;
+
+	size = NLMSG_ALIGN(sizeof(struct ifinfomsg))
 	       + nla_total_size(IFNAMSIZ) /* IFLA_IFNAME */
 	       + nla_total_size(IFALIASZ) /* IFLA_IFALIAS */
 	       + nla_total_size(IFNAMSIZ) /* IFLA_QDISC */
 	       + nla_total_size_64bit(sizeof(struct rtnl_link_ifmap))
-	       + nla_total_size(sizeof(struct rtnl_link_stats))
-	       + nla_total_size_64bit(sizeof(struct rtnl_link_stats64))
 	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_ADDRESS */
 	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_BROADCAST */
 	       + nla_total_size(4) /* IFLA_TXQLEN */
···
 	       + nla_total_size(2)  /* IFLA_HEADROOM */
 	       + nla_total_size(2)  /* IFLA_TAILROOM */
 	       + 0;
+
+	if (!(ext_filter_mask & RTEXT_FILTER_SKIP_STATS))
+		size += nla_total_size(sizeof(struct rtnl_link_stats)) +
+			nla_total_size_64bit(sizeof(struct rtnl_link_stats64));
+
+	return size;
 }
 
 static int rtnl_vf_ports_fill(struct sk_buff *skb, struct net_device *dev)
···
 	if (rtnl_phys_switch_id_fill(skb, dev))
 		goto nla_put_failure;
 
-	if (rtnl_fill_stats(skb, dev))
+	if (!(ext_filter_mask & RTEXT_FILTER_SKIP_STATS) &&
+	    rtnl_fill_stats(skb, dev))
 		goto nla_put_failure;
 
 	if (rtnl_fill_vf(skb, dev, ext_filter_mask))