Subject: Re: [PATCH net-next v5 02/16] net: Implement netdev_nl_queue_create_doit

From: Stanislav Fomichev <[email-masked]>
Date: Sun, 11 Jan 2026 12:55:23 -0800

On 01/09, Daniel Borkmann wrote:
> Implement netdev_nl_queue_create_doit which creates a new rx queue in a
> virtual netdev and then leases it to a rx queue in a physical netdev.
> 
> Example with ynl client:
> 
>   # ./pyynl/cli.py \
>       --spec ~/netlink/specs/netdev.yaml \
>       --do queue-create \
>       --json '{"ifindex": 8, "type": "rx", "lease": {"ifindex": 4, "queue": {"type": "rx", "id": 15}}}'
>   {'id': 1}
> 
> Note that the netdevice locking order is always from the virtual to
> the physical device.
> 
> Signed-off-by: Daniel Borkmann <[email-masked]>
> Co-developed-by: David Wei <[email-masked]>
> Signed-off-by: David Wei <[email-masked]>
> ---
>  include/net/netdev_queues.h   |  19 ++++-
>  include/net/netdev_rx_queue.h |   9 ++-
>  include/net/xdp_sock_drv.h    |   2 +-
>  net/core/dev.c                |   7 ++
>  net/core/dev.h                |   2 +
>  net/core/netdev-genl.c        | 146 +++++++++++++++++++++++++++++++++-
>  net/core/netdev_queues.c      |  57 +++++++++++++
>  net/core/netdev_rx_queue.c    |  50 +++++++++++-
>  net/xdp/xsk.c                 |   2 +-
>  9 files changed, 282 insertions(+), 12 deletions(-)
> 
> diff --git a/include/net/netdev_queues.h b/include/net/netdev_queues.h
> index cd00e0406cf4..f65319a6fb87 100644
> --- a/include/net/netdev_queues.h
> +++ b/include/net/netdev_queues.h
> @@ -130,6 +130,11 @@ void netdev_stat_queue_sum(struct net_device *netdev,
>   * @ndo_queue_get_dma_dev: Get dma device for zero-copy operations to be used
>   *			   for this queue. Return NULL on error.
>   *
> + * @ndo_queue_create: Create a new RX queue which can be leased to another queue.
> + *		      Ops on this queue are redirected to the leased queue e.g.
> + *		      when opening a memory provider. Return the new queue id on
> + *		      success. Return negative error code on failure.
> + *
>   * Note that @ndo_queue_mem_alloc and @ndo_queue_mem_free may be called while
>   * the interface is closed. @ndo_queue_start and @ndo_queue_stop will only
>   * be called for an interface which is open.
> @@ -149,9 +154,12 @@ struct netdev_queue_mgmt_ops {
>  						  int idx);
>  	struct device *		(*ndo_queue_get_dma_dev)(struct net_device *dev,
>  							 int idx);
> +	int			(*ndo_queue_create)(struct net_device *dev);
>  };
>  
> -bool netif_rxq_has_unreadable_mp(struct net_device *dev, int idx);
> +bool netif_rxq_has_unreadable_mp(struct net_device *dev, unsigned int rxq_idx);
> +bool netif_rxq_has_mp(struct net_device *dev, unsigned int rxq_idx);
> +bool netif_rxq_is_leased(struct net_device *dev, unsigned int rxq_idx);
>  
>  /**
>   * DOC: Lockless queue stopping / waking helpers.
> @@ -329,5 +337,10 @@ static inline void netif_subqueue_sent(const struct net_device *dev,
>  	})
>  
>  struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx);
> -
> -#endif
> +bool netdev_can_create_queue(const struct net_device *dev,
> +			     struct netlink_ext_ack *extack);
> +bool netdev_can_lease_queue(const struct net_device *dev,
> +			    struct netlink_ext_ack *extack);
> +bool netdev_queue_busy(struct net_device *dev, int idx,
> +		       struct netlink_ext_ack *extack);
> +#endif /* _LINUX_NET_QUEUES_H */
> diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
> index 8cdcd138b33f..1cacc2451516 100644
> --- a/include/net/netdev_rx_queue.h
> +++ b/include/net/netdev_rx_queue.h
> @@ -28,6 +28,8 @@ struct netdev_rx_queue {
>  #endif
>  	struct napi_struct		*napi;
>  	struct pp_memory_provider_params mp_params;
> +	struct netdev_rx_queue		*lease;
> +	netdevice_tracker		lease_tracker;
>  } ____cacheline_aligned_in_smp;
>  
>  /*
> @@ -57,5 +59,8 @@ get_netdev_rx_queue_index(struct netdev_rx_queue *queue)
>  }
>  
>  int netdev_rx_queue_restart(struct net_device *dev, unsigned int rxq);
> -
> -#endif
> +void netdev_rx_queue_lease(struct netdev_rx_queue *rxq_dst,
> +			   struct netdev_rx_queue *rxq_src);
> +void netdev_rx_queue_unlease(struct netdev_rx_queue *rxq_dst,
> +			     struct netdev_rx_queue *rxq_src);
> +#endif /* _LINUX_NETDEV_RX_QUEUE_H */
> diff --git a/include/net/xdp_sock_drv.h b/include/net/xdp_sock_drv.h
> index 242e34f771cc..c07cfb431eac 100644
> --- a/include/net/xdp_sock_drv.h
> +++ b/include/net/xdp_sock_drv.h
> @@ -28,7 +28,7 @@ void xsk_tx_completed(struct xsk_buff_pool *pool, u32 nb_entries);
>  bool xsk_tx_peek_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc);
>  u32 xsk_tx_peek_release_desc_batch(struct xsk_buff_pool *pool, u32 max);
>  void xsk_tx_release(struct xsk_buff_pool *pool);
> -struct xsk_buff_pool *xsk_get_pool_from_qid(struct net_device *dev,
> +struct xsk_buff_pool *xsk_get_pool_from_qid(const struct net_device *dev,
>  					    u16 queue_id);
>  void xsk_set_rx_need_wakeup(struct xsk_buff_pool *pool);
>  void xsk_set_tx_need_wakeup(struct xsk_buff_pool *pool);
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 36dc5199037e..c2b64ffeb9e6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1102,6 +1102,13 @@ netdev_get_by_index_lock_ops_compat(struct net *net, int ifindex)
>  	return __netdev_put_lock_ops_compat(dev, net);
>  }
>  
> +struct net_device *
> +netdev_put_lock(struct net_device *dev, netdevice_tracker *tracker)
> +{
> +	netdev_tracker_free(dev, tracker);
> +	return __netdev_put_lock(dev, dev_net(dev));
> +}
> +
>  struct net_device *
>  netdev_xa_find_lock(struct net *net, struct net_device *dev,
>  		    unsigned long *index)
> diff --git a/net/core/dev.h b/net/core/dev.h
> index da18536cbd35..9bcb76b325d0 100644
> --- a/net/core/dev.h
> +++ b/net/core/dev.h
> @@ -30,6 +30,8 @@ netdev_napi_by_id_lock(struct net *net, unsigned int napi_id);
>  struct net_device *dev_get_by_napi_id(unsigned int napi_id);
>  
>  struct net_device *__netdev_put_lock(struct net_device *dev, struct net *net);
> +struct net_device *netdev_put_lock(struct net_device *dev,
> +				   netdevice_tracker *tracker);
>  struct net_device *
>  netdev_xa_find_lock(struct net *net, struct net_device *dev,
>  		    unsigned long *index);
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index aae75431858d..cd4dc4eef029 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -1122,7 +1122,151 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>  
>  int netdev_nl_queue_create_doit(struct sk_buff *skb, struct genl_info *info)
>  {
> -	return -EOPNOTSUPP;
> +	const int qmaxtype = ARRAY_SIZE(netdev_queue_id_nl_policy) - 1;
> +	const int lmaxtype = ARRAY_SIZE(netdev_lease_nl_policy) - 1;
> +	int err, ifindex, ifindex_lease, queue_id, queue_id_lease;
> +	struct nlattr *qtb[ARRAY_SIZE(netdev_queue_id_nl_policy)];
> +	struct nlattr *ltb[ARRAY_SIZE(netdev_lease_nl_policy)];
> +	struct netdev_rx_queue *rxq, *rxq_lease;
> +	struct net_device *dev, *dev_lease;
> +	netdevice_tracker dev_tracker;
> +	struct nlattr *nest;
> +	struct sk_buff *rsp;
> +	void *hdr;
> +
> +	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_IFINDEX) ||
> +	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_TYPE) ||
> +	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_LEASE))
> +		return -EINVAL;
> +	if (nla_get_u32(info->attrs[NETDEV_A_QUEUE_TYPE]) !=
> +	    NETDEV_QUEUE_TYPE_RX) {
> +		NL_SET_BAD_ATTR(info->extack, info->attrs[NETDEV_A_QUEUE_TYPE]);
> +		return -EINVAL;
> +	}
> +
> +	ifindex = nla_get_u32(info->attrs[NETDEV_A_QUEUE_IFINDEX]);
> +
> +	nest = info->attrs[NETDEV_A_QUEUE_LEASE];
> +	err = nla_parse_nested(ltb, lmaxtype, nest,
> +			       netdev_lease_nl_policy, info->extack);
> +	if (err < 0)
> +		return err;
> +	if (NL_REQ_ATTR_CHECK(info->extack, nest, ltb, NETDEV_A_LEASE_IFINDEX) ||
> +	    NL_REQ_ATTR_CHECK(info->extack, nest, ltb, NETDEV_A_LEASE_QUEUE))
> +		return -EINVAL;
> +	if (ltb[NETDEV_A_LEASE_NETNS_ID]) {
> +		NL_SET_BAD_ATTR(info->extack, ltb[NETDEV_A_LEASE_NETNS_ID]);
> +		return -EINVAL;
> +	}
> +
> +	ifindex_lease = nla_get_u32(ltb[NETDEV_A_LEASE_IFINDEX]);
> +
> +	nest = ltb[NETDEV_A_LEASE_QUEUE];
> +	err = nla_parse_nested(qtb, qmaxtype, nest,
> +			       netdev_queue_id_nl_policy, info->extack);
> +	if (err < 0)
> +		return err;
> +	if (NL_REQ_ATTR_CHECK(info->extack, nest, qtb, NETDEV_A_QUEUE_ID) ||
> +	    NL_REQ_ATTR_CHECK(info->extack, nest, qtb, NETDEV_A_QUEUE_TYPE))
> +		return -EINVAL;
> +	if (nla_get_u32(qtb[NETDEV_A_QUEUE_TYPE]) != NETDEV_QUEUE_TYPE_RX) {
> +		NL_SET_BAD_ATTR(info->extack, qtb[NETDEV_A_QUEUE_TYPE]);
> +		return -EINVAL;
> +	}
> +	if (ifindex == ifindex_lease) {
> +		NL_SET_ERR_MSG(info->extack,
> +			       "Lease ifindex cannot be the same as queue creation ifindex");
> +		return -EINVAL;
> +	}
> +
> +	queue_id_lease = nla_get_u32(qtb[NETDEV_A_QUEUE_ID]);
> +
> +	rsp = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
> +	if (!rsp)
> +		return -ENOMEM;
> +
> +	hdr = genlmsg_iput(rsp, info);
> +	if (!hdr) {
> +		err = -EMSGSIZE;
> +		goto err_genlmsg_free;
> +	}
> +
> +	/* Locking order is always from the virtual to the physical device
> +	 * since this is also the same order when applications open the
> +	 * memory provider later on.
> +	 */
> +	dev = netdev_get_by_index_lock(genl_info_net(info), ifindex);
> +	if (!dev) {
> +		err = -ENODEV;
> +		goto err_genlmsg_free;
> +	}
> +	if (!netdev_can_create_queue(dev, info->extack)) {
> +		err = -EINVAL;
> +		goto err_unlock_dev;
> +	}
> +
> +	dev_lease = netdev_get_by_index(genl_info_net(info), ifindex_lease,
> +					&dev_tracker, GFP_KERNEL);
> +	if (!dev_lease) {
> +		err = -ENODEV;
> +		goto err_unlock_dev;
> +	}
> +	if (!netdev_can_lease_queue(dev_lease, info->extack)) {
> +		netdev_put(dev_lease, &dev_tracker);
> +		err = -EINVAL;
> +		goto err_unlock_dev;
> +	}
> +
> +	dev_lease = netdev_put_lock(dev_lease, &dev_tracker);
> +	if (!dev_lease) {
> +		err = -ENODEV;
> +		goto err_unlock_dev;
> +	}
> +	if (queue_id_lease >= dev_lease->real_num_rx_queues) {
> +		err = -ERANGE;
> +		NL_SET_BAD_ATTR(info->extack, qtb[NETDEV_A_QUEUE_ID]);
> +		goto err_unlock_dev_lease;
> +	}
> +	if (netdev_queue_busy(dev_lease, queue_id_lease, info->extack)) {
> +		err = -EBUSY;
> +		goto err_unlock_dev_lease;
> +	}
> +
> +	rxq_lease = __netif_get_rx_queue(dev_lease, queue_id_lease);
> +	rxq = __netif_get_rx_queue(dev, dev->real_num_rx_queues - 1);
> +
> +	if (rxq->lease && rxq->lease->dev != dev_lease) {
> +		err = -EOPNOTSUPP;
> +		NL_SET_ERR_MSG(info->extack,
> +			       "Leasing multiple queues from different devices not supported");
> +		goto err_unlock_dev_lease;
> +	}
> +
> +	err = queue_id = dev->queue_mgmt_ops->ndo_queue_create(dev);
> +	if (err < 0) {
> +		NL_SET_ERR_MSG(info->extack,
> +			       "Device is unable to create a new queue");
> +		goto err_unlock_dev_lease;
> +	}
> +
> +	rxq = __netif_get_rx_queue(dev, queue_id);
> +	netdev_rx_queue_lease(rxq, rxq_lease);
> +
> +	nla_put_u32(rsp, NETDEV_A_QUEUE_ID, queue_id);
> +	genlmsg_end(rsp, hdr);
> +
> +	netdev_unlock(dev_lease);
> +	netdev_unlock(dev);
> +
> +	return genlmsg_reply(rsp, info);
> +
> +err_unlock_dev_lease:
> +	netdev_unlock(dev_lease);
> +err_unlock_dev:
> +	netdev_unlock(dev);
> +err_genlmsg_free:
> +	nlmsg_free(rsp);
> +	return err;
>  }
>  
>  void netdev_nl_sock_priv_init(struct netdev_nl_sock *priv)
> diff --git a/net/core/netdev_queues.c b/net/core/netdev_queues.c
> index 251f27a8307f..fae92ee090c4 100644
> --- a/net/core/netdev_queues.c
> +++ b/net/core/netdev_queues.c
> @@ -1,6 +1,8 @@
>  // SPDX-License-Identifier: GPL-2.0-or-later
>  
>  #include <net/netdev_queues.h>
> +#include <net/netdev_rx_queue.h>
> +#include <net/xdp_sock_drv.h>
>  
>  /**
>   * netdev_queue_get_dma_dev() - get dma device for zero-copy operations
> @@ -25,3 +27,58 @@ struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx)
>  	return dma_dev && dma_dev->dma_mask ? dma_dev : NULL;
>  }
>  
> +bool netdev_can_create_queue(const struct net_device *dev,
> +			     struct netlink_ext_ack *extack)
> +{
> +	if (dev->dev.parent) {
> +		NL_SET_ERR_MSG(extack, "Device is not a virtual device");
> +		return false;
> +	}
> +	if (!dev->queue_mgmt_ops ||
> +	    !dev->queue_mgmt_ops->ndo_queue_create) {
> +		NL_SET_ERR_MSG(extack, "Device does not support queue creation");
> +		return false;
> +	}
> +	if (dev->real_num_rx_queues < 1 ||
> +	    dev->real_num_tx_queues < 1) {
> +		NL_SET_ERR_MSG(extack, "Device must have at least one real queue");
> +		return false;
> +	}
> +	return true;
> +}
> +
> +bool netdev_can_lease_queue(const struct net_device *dev,
> +			    struct netlink_ext_ack *extack)
> +{
> +	if (!dev->dev.parent) {
> +		NL_SET_ERR_MSG(extack, "Lease device is a virtual device");
> +		return false;
> +	}
> +	if (!netif_device_present(dev)) {
> +		NL_SET_ERR_MSG(extack, "Lease device has been removed from the system");
> +		return false;
> +	}
> +	if (!dev->queue_mgmt_ops) {
> +		NL_SET_ERR_MSG(extack, "Lease device does not support queue management operations");
> +		return false;
> +	}
> +	return true;
> +}
> +
> +bool netdev_queue_busy(struct net_device *dev, int idx,
> +		       struct netlink_ext_ack *extack)
> +{
> +	if (netif_rxq_is_leased(dev, idx)) {
> +		NL_SET_ERR_MSG(extack, "Lease device queue is already leased");
> +		return true;
> +	}
> +	if (xsk_get_pool_from_qid(dev, idx)) {
> +		NL_SET_ERR_MSG(extack, "Lease device queue in use by AF_XDP");
> +		return true;
> +	}
> +	if (netif_rxq_has_mp(dev, idx)) {
> +		NL_SET_ERR_MSG(extack, "Lease device queue in use by memory provider");
> +		return true;
> +	}
> +	return false;
> +}
> diff --git a/net/core/netdev_rx_queue.c b/net/core/netdev_rx_queue.c
> index c7d9341b7630..ed85dfb434a0 100644
> --- a/net/core/netdev_rx_queue.c
> +++ b/net/core/netdev_rx_queue.c
> @@ -9,15 +9,57 @@
>  
>  #include "page_pool_priv.h"
>  
> -/* See also page_pool_is_unreadable() */
> -bool netif_rxq_has_unreadable_mp(struct net_device *dev, int idx)
> +void netdev_rx_queue_lease(struct netdev_rx_queue *rxq_dst,
> +			   struct netdev_rx_queue *rxq_src)
> +{
> +	netdev_assert_locked(rxq_src->dev);
> +	netdev_assert_locked(rxq_dst->dev);
> +
> +	WARN_ON_ONCE(READ_ONCE(rxq_src->dev->reg_state) == NETREG_UNREGISTERING);

I might have missed some of your discussions with Jakub, but what is
this WARN_ON_ONCE above trying to catch? And why not handle it explicitly
(via returning an error from netdev_rx_queue_lease)?