[PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Eric Dumazet <edumazet@google.com>]

iproute2 can spend considerable amount of time in ll_init_map()
or ll_link_get() to dump verbose netdev attributes, contributing
to RTNL pressure.

Add RTEXT_FILTER_TERSE_DUMP new flag so that rtnl_fill_ifinfo()
limits its output to:

- struct nlmsghdr
- IFLA_IFNAME
- IFLA_PROP_LIST

We can later avoid using RTNL when RTEXT_FILTER_TERSE_DUMP
is requested, as none of these attributes need RTNL.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/uapi/linux/rtnetlink.h |  1 +
 net/core/rtnetlink.c           | 31 ++++++++++++++++++++++---------
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index dab9493c791b8465c6476990f42c4ee5ae82da2d..4b1dbd554e5c72c90d2416f7ade37956ad5472b7 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -840,6 +840,7 @@ enum {
 #define RTEXT_FILTER_CFM_CONFIG	(1 << 5)
 #define RTEXT_FILTER_CFM_STATUS	(1 << 6)
 #define RTEXT_FILTER_MST	(1 << 7)
+#define RTEXT_FILTER_TERSE_DUMP	(1 << 8)
 
 /* End of information exported to user level */
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index b613bb6e07df6586aa06e7a59c8384dcedffeeef..7a9a769d142b6826d7fb01b599a4d9e0ae09a97d 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1295,7 +1295,12 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
 
 	size = NLMSG_ALIGN(sizeof(struct ifinfomsg))
 	       + nla_total_size(IFNAMSIZ) /* IFLA_IFNAME */
-	       + nla_total_size(IFALIASZ) /* IFLA_IFALIAS */
+	       + rtnl_prop_list_size(dev);
+
+	if (ext_filter_mask & RTEXT_FILTER_TERSE_DUMP)
+		return size;
+
+	size += nla_total_size(IFALIASZ) /* IFLA_IFALIAS */
 	       + nla_total_size(IFNAMSIZ) /* IFLA_QDISC */
 	       + nla_total_size_64bit(sizeof(struct rtnl_link_ifmap))
 	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_ADDRESS */
@@ -1342,7 +1347,6 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
 	       + nla_total_size(4)  /* IFLA_CARRIER_DOWN_COUNT */
 	       + nla_total_size(4)  /* IFLA_MIN_MTU */
 	       + nla_total_size(4)  /* IFLA_MAX_MTU */
-	       + rtnl_prop_list_size(dev)
 	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_PERM_ADDRESS */
 	       + rtnl_devlink_port_size(dev)
 	       + rtnl_dpll_pin_size(dev)
@@ -1940,15 +1944,18 @@ static int rtnl_fill_alt_ifnames(struct sk_buff *skb,
 	struct netdev_name_node *name_node;
 	int count = 0;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(name_node, &dev->name_node->list, list) {
-		if (nla_put_string(skb, IFLA_ALT_IFNAME, name_node->name))
+		if (nla_put_string(skb, IFLA_ALT_IFNAME, name_node->name)) {
+			rcu_read_unlock();
 			return -EMSGSIZE;
+		}
 		count++;
 	}
+	rcu_read_unlock();
 	return count;
 }
 
-/* RCU protected. */
 static int rtnl_fill_prop_list(struct sk_buff *skb,
 			       const struct net_device *dev)
 {
@@ -2071,13 +2078,20 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 	ifm->ifi_flags = netif_get_flags(dev);
 	ifm->ifi_change = change;
 
-	if (tgt_netnsid >= 0 && nla_put_s32(skb, IFLA_TARGET_NETNSID, tgt_netnsid))
-		goto nla_put_failure;
-
 	netdev_copy_name(dev, devname);
 	if (nla_put_string(skb, IFLA_IFNAME, devname))
 		goto nla_put_failure;
 
+	if (rtnl_fill_prop_list(skb, dev))
+		goto nla_put_failure;
+
+	if (ext_filter_mask & RTEXT_FILTER_TERSE_DUMP)
+		goto end;
+
+	if (tgt_netnsid >= 0 &&
+	    nla_put_s32(skb, IFLA_TARGET_NETNSID, tgt_netnsid))
+		goto nla_put_failure;
+
 	if (nla_put_u32(skb, IFLA_TXQLEN, READ_ONCE(dev->tx_queue_len)) ||
 	    nla_put_u8(skb, IFLA_OPERSTATE,
 		       netif_running(dev) ? READ_ONCE(dev->operstate) :
@@ -2190,8 +2204,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 		goto nla_put_failure_rcu;
 	if (rtnl_fill_link_ifmap(skb, dev))
 		goto nla_put_failure_rcu;
-	if (rtnl_fill_prop_list(skb, dev))
-		goto nla_put_failure_rcu;
 	rcu_read_unlock();
 
 	if (dev->dev.parent &&
@@ -2210,6 +2222,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 	if (rtnl_fill_dpll_pin(skb, dev))
 		goto nla_put_failure;
 
+end:
 	nlmsg_end(skb, nlh);
 	return 0;
 
-- 
2.54.0.563.g4f69b47b94-goog