Re: [PATCH net-next v3 14/23] net: add queue config validation callback

[Mina Almasry <almasrymina@google.com>]

On Mon, Aug 18, 2025 at 6:56 AM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> From: Jakub Kicinski <kuba@kernel.org>
>
> I imagine (tm) that as the number of per-queue configuration
> options grows some of them may conflict for certain drivers.
> While the drivers can obviously do all the validation locally
> doing so is fairly inconvenient as the config is fed to drivers
> piecemeal via different ops (for different params and NIC-wide
> vs per-queue).
>
> Add a centralized callback for validating the queue config
> in queue ops. The callback gets invoked before each queue restart
> and when ring params are modified.
>
> For NIC-wide changes the callback gets invoked for each active
> (or active to-be) queue, and additionally with a negative queue
> index for NIC-wide defaults. The NIC-wide check is needed in
> case all queues have an override active when NIC-wide setting
> is changed to an unsupported one. Alternatively we could check
> the settings when new queues are enabled (in the channel API),
> but accepting invalid config is a bad idea. Users may expect
> that resetting a queue override will always work.
>
> The "trick" of passing a negative index is a bit ugly, we may
> want to revisit if it causes confusion and bugs. Existing drivers
> don't care about the index so it "just works".
>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  include/net/netdev_queues.h | 12 ++++++++++++
>  net/core/dev.h              |  2 ++
>  net/core/netdev_config.c    | 20 ++++++++++++++++++++
>  net/core/netdev_rx_queue.c  |  6 ++++++
>  net/ethtool/rings.c         |  5 +++++
>  5 files changed, 45 insertions(+)
>
> diff --git a/include/net/netdev_queues.h b/include/net/netdev_queues.h
> index b850cff71d12..d0cc475ec51e 100644
> --- a/include/net/netdev_queues.h
> +++ b/include/net/netdev_queues.h
> @@ -147,6 +147,14 @@ void netdev_stat_queue_sum(struct net_device *netdev,
>   *                     defaults. Queue config structs are passed to this
>   *                     helper before the user-requested settings are applied.
>   *
> + * @ndo_queue_cfg_validate: (Optional) Check if queue config is supported.
> + *                     Called when configuration affecting a queue may be
> + *                     changing, either due to NIC-wide config, or config
> + *                     scoped to the queue at a specified index.
> + *                     When NIC-wide config is changed the callback will
> + *                     be invoked for all queues, and in addition to that
> + *                     with a negative queue index for the base settings.
> + *
>   * @ndo_queue_mem_alloc: Allocate memory for an RX queue at the specified index.
>   *                      The new memory is written at the specified address.
>   *
> @@ -167,6 +175,10 @@ struct netdev_queue_mgmt_ops {
>         void    (*ndo_queue_cfg_defaults)(struct net_device *dev,
>                                           int idx,
>                                           struct netdev_queue_config *qcfg);
> +       int     (*ndo_queue_cfg_validate)(struct net_device *dev,
> +                                         int idx,
> +                                         struct netdev_queue_config *qcfg,
> +                                         struct netlink_ext_ack *extack);
>         int     (*ndo_queue_mem_alloc)(struct net_device *dev,
>                                        struct netdev_queue_config *qcfg,
>                                        void *per_queue_mem,
> diff --git a/net/core/dev.h b/net/core/dev.h
> index a553a0f1f846..523d50e6f88d 100644
> --- a/net/core/dev.h
> +++ b/net/core/dev.h
> @@ -99,6 +99,8 @@ void netdev_free_config(struct net_device *dev);
>  int netdev_reconfig_start(struct net_device *dev);
>  void __netdev_queue_config(struct net_device *dev, int rxq,
>                            struct netdev_queue_config *qcfg, bool pending);
> +int netdev_queue_config_revalidate(struct net_device *dev,
> +                                  struct netlink_ext_ack *extack);
>
>  /* netdev management, shared between various uAPI entry points */
>  struct netdev_name_node {
> diff --git a/net/core/netdev_config.c b/net/core/netdev_config.c
> index bad2d53522f0..fc700b77e4eb 100644
> --- a/net/core/netdev_config.c
> +++ b/net/core/netdev_config.c
> @@ -99,3 +99,23 @@ void netdev_queue_config(struct net_device *dev, int rxq,
>         __netdev_queue_config(dev, rxq, qcfg, true);
>  }
>  EXPORT_SYMBOL(netdev_queue_config);
> +
> +int netdev_queue_config_revalidate(struct net_device *dev,
> +                                  struct netlink_ext_ack *extack)
> +{
> +       const struct netdev_queue_mgmt_ops *qops = dev->queue_mgmt_ops;
> +       struct netdev_queue_config qcfg;
> +       int i, err;
> +
> +       if (!qops || !qops->ndo_queue_cfg_validate)
> +               return 0;
> +
> +       for (i = -1; i < (int)dev->real_num_rx_queues; i++) {
> +               netdev_queue_config(dev, i, &qcfg);

This function as written feels very useless tbh. There is no config
passed in from the caller, so the function does a netdev_queue_config,
which grabs the current-or-default-config (I'm not sure which tbh),
and then validates that is applicable. But of course the current or
default configs can be applied, right?

I thought there would be a refactor in a future patch that makes this
function useful, but I don't see one.

The qcfg being applied needs to be passed in by the caller of this
function, no? That would make sense to me (the caller is wondering if
this new config is applicable).

-- 
Thanks,
Mina