net: Add queue-create operation

net: Add queue-create operation

Add a ynl netdev family operation called queue-create that creates a
new queue on a netdevice:

      name: queue-create
      attribute-set: queue
      flags: [admin-perm]
      do:
        request:
          attributes:
            - ifindex
            - type
            - lease
        reply: &queue-create-op
          attributes:
            - id

This is a generic operation such that it can be extended for various
use cases in future. Right now it is mandatory to specify ifindex,
the queue type which is enforced to rx and a lease. The newly created
queue id is returned to the caller.

A queue from a virtual device can have a lease which refers to another
queue from a physical device. This is useful for memory providers
and AF_XDP operations which take an ifindex and queue id to allow
applications to bind against virtual devices in containers. The lease
couples both queues together and allows to proxy the operations from
a virtual device in a container to the physical device.

In future, the nested lease attribute can be lifted and made optional
for other use-cases such as dynamic queue creation for physical
netdevs. The lack of lease and the specification of the physical
device as an ifindex will imply that we need a real queue to be
allocated. Similarly, the queue type enforcement to rx can then be
lifted as well to support tx.

An early implementation had only driver-specific integration [0], but
in order for other virtual devices to reuse, it makes sense to have
this as a generic API in core net.

For leasing queues, the virtual netdev must have real_num_rx_queue
less than num_rx_queues at the time of calling queue-create. The
queue-type must be rx as only rx queues are supported for leasing
for now. We also enforce that the queue-create ifindex must point
to a virtual device, and that the nested lease attribute's ifindex
must point to a physical device. The nested lease attribute set
contains a netns-id attribute which is currently only intended for
dumping as part of the queue-get operation. Also, it is modeled as
an s32 type similarly as done elsewhere in the stack.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Co-developed-by: David Wei <dw@davidwei.uk>
Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://bpfconf.ebpf.io/bpfconf2025/bpfconf2025_material/lsfmmbpf_2025_netkit_borkmann.pdf
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260115082603.219152-2-daniel@iogearbox.net
Signed-off-by: Paolo Abeni <pabeni@redhat.com>