rtnetlink: add RTEXT_FILTER_NAME_ONLY support

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

- struct nlmsghdr
- IFLA_IFNAME
- IFLA_PROP_LIST (alternate names)

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

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260511070244.971028-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index dab9493c791b8465c6476990f42c4ee5ae82da2d..27265fd31e5fc99c312b42f3b1f072419b56ee0b 100644 (file)
--- 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_NAME_ONLY (1 << 8)
 
 /* End of information exported to user level */
 

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index df042da422ef3137ed67efaf8d243cc6b1fec6c7..70fde922b3718d753caf4874047d0b55ec649ef2 100644 (file)
--- 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_NAME_ONLY)
+               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)
@@ -1941,15 +1945,18 @@ 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)
 {
@@ -2072,13 +2079,20 @@ 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_NAME_ONLY)
+               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) :
@@ -2191,8 +2205,6 @@ 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 &&
@@ -2211,6 +2223,7 @@ 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;