Re: [PATCH net-next v2] netdev-genl: Elide napi_id when not present

[Eric Dumazet]

On Mon, Feb 3, 2025 at 8:17 PM Joe Damato <jdamato@xxxxxxxxxx> wrote:
>
> There are at least two cases where napi_id may not present and the
> napi_id should be elided:
>
> 1. Queues could be created, but napi_enable may not have been called
>    yet. In this case, there may be a NAPI but it may not have an ID and
>    output of a napi_id should be elided.
>
> 2. TX-only NAPIs currently do not have NAPI IDs. If a TX queue happens
>    to be linked with a TX-only NAPI, elide the NAPI ID from the netlink
>    output as a NAPI ID of 0 is not useful for users.
>
> Signed-off-by: Joe Damato <jdamato@xxxxxxxxxx>
> ---
>  v2:
>    - Updated to elide NAPI IDs for RX queues which may have not called
>      napi_enable yet.
>
>  rfc: https://lore.kernel.org/lkml/20250128163038.429864-1-jdamato@xxxxxxxxxx/
>  net/core/netdev-genl.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index 715f85c6b62e..a97d3b99f6cd 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -385,9 +385,10 @@ netdev_nl_queue_fill_one(struct sk_buff *rsp, struct net_device *netdev,
>         switch (q_type) {
>         case NETDEV_QUEUE_TYPE_RX:
>                 rxq = __netif_get_rx_queue(netdev, q_idx);
> -               if (rxq->napi && nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
> -                                            rxq->napi->napi_id))
> -                       goto nla_put_failure;
> +               if (rxq->napi && rxq->napi->napi_id >= MIN_NAPI_ID)
> +                       if (nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
> +                                       rxq->napi->napi_id))
> +                               goto nla_put_failure;
>
>                 binding = rxq->mp_params.mp_priv;
>                 if (binding &&
> @@ -397,9 +398,10 @@ netdev_nl_queue_fill_one(struct sk_buff *rsp, struct net_device *netdev,
>                 break;
>         case NETDEV_QUEUE_TYPE_TX:
>                 txq = netdev_get_tx_queue(netdev, q_idx);
> -               if (txq->napi && nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
> -                                            txq->napi->napi_id))
> -                       goto nla_put_failure;
> +               if (txq->napi && txq->napi->napi_id >= MIN_NAPI_ID)
> +                       if (nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
> +                                       txq->napi->napi_id))
> +                               goto nla_put_failure;
>         }

Hi Joe

This might be time to add helpers, we now have these checks about
MIN_NAPI_ID all around the places.

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index c39a426ebf52038b493b145e65e2d3d7f0c74e4c..741fa77547001aa5d966763c81540ee9210c949e
100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -24,6 +24,11 @@
  */
 #define MIN_NAPI_ID ((unsigned int)(NR_CPUS + 1))

+static inline bool napi_id_valid(unsigned int napi_id)
+{
+       return napi_id >= MIN_NAPI_ID;
+}
+
 #define BUSY_POLL_BUDGET 8

 #ifdef CONFIG_NET_RX_BUSY_POLL
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 715f85c6b62eabcc61a10065f98cc914f5f0d975..b5c4e42351e67d73c0aa879156eea431d4baf7aa
100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -364,6 +364,13 @@ int netdev_nl_napi_set_doit(struct sk_buff *skb,
struct genl_info *info)
        return err;
 }

+static int nla_put_napi_id(struct sk_buff *skb, const struct napi_struct *napi)
+{
+       if (napi && napi_id_valid(napi->napi_id))
+               return nla_put_u32(skb, NETDEV_A_QUEUE_NAPI_ID, napi->napi_id);
+       return 0;
+}
+
 static int
 netdev_nl_queue_fill_one(struct sk_buff *rsp, struct net_device *netdev,
                         u32 q_idx, u32 q_type, const struct genl_info *info)
@@ -385,8 +392,7 @@ netdev_nl_queue_fill_one(struct sk_buff *rsp,
struct net_device *netdev,
        switch (q_type) {
        case NETDEV_QUEUE_TYPE_RX:
                rxq = __netif_get_rx_queue(netdev, q_idx);
-               if (rxq->napi && nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
-                                            rxq->napi->napi_id))
+               if (nla_put_napi_id(rsp, rxq->napi))
                        goto nla_put_failure;

                binding = rxq->mp_params.mp_priv;
@@ -397,8 +403,7 @@ netdev_nl_queue_fill_one(struct sk_buff *rsp,
struct net_device *netdev,
                break;
        case NETDEV_QUEUE_TYPE_TX:
                txq = netdev_get_tx_queue(netdev, q_idx);
-               if (txq->napi && nla_put_u32(rsp, NETDEV_A_QUEUE_NAPI_ID,
-                                            txq->napi->napi_id))
+               if (nla_put_napi_id(rsp, txq->napi))
                        goto nla_put_failure;
        }