[PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Eric Dumazet]

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

Re: [PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Eric Dumazet]

On Thu, May 7, 2026 at 10:45 AM Eric Dumazet <edumazet@google.com> wrote:
>
> 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>

Wrong patch title, this targets net-next tree (obviously).

Thanks.

Re: [PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Kuniyuki Iwashima]

On Thu, May 7, 2026 at 10:45 AM Eric Dumazet <edumazet@google.com> wrote:
>
> 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>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

Re: [PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Jakub Kicinski]

On Thu,  7 May 2026 17:45:47 +0000 Eric Dumazet wrote:
> We can later avoid using RTNL when RTEXT_FILTER_TERSE_DUMP
> is requested, as none of these attributes need RTNL.

Since this is uAPI I think we need a better name?
TERSE_DUMP doesn't explain much, my first thought was that you'll just
trim some ancient attributes to make things smaller. Sounds like you
want it to be lockless. Also GET will effectively support this bit
too so _DUMP is a lie.

Maybe RTEXT_FILTER_LOCKLESS or RTEXT_FILTER_NAME_ONLY ?

Re: [PATCH net] rtnetlink: add RTEXT_FILTER_TERSE_DUMP support

[Eric Dumazet]

On Fri, May 8, 2026 at 4:18 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu,  7 May 2026 17:45:47 +0000 Eric Dumazet wrote:
> > We can later avoid using RTNL when RTEXT_FILTER_TERSE_DUMP
> > is requested, as none of these attributes need RTNL.
>
> Since this is uAPI I think we need a better name?
> TERSE_DUMP doesn't explain much, my first thought was that you'll just
> trim some ancient attributes to make things smaller. Sounds like you
> want it to be lockless. Also GET will effectively support this bit
> too so _DUMP is a lie.
>
> Maybe RTEXT_FILTER_LOCKLESS or RTEXT_FILTER_NAME_ONLY ?

SGTM, thanks.