net: Implement netdev_nl_queue_create_doit

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:

  # ynl --family netdev --output-json --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 <daniel@iogearbox.net>
Co-developed-by: David Wei <dw@davidwei.uk>
Signed-off-by: David Wei <dw@davidwei.uk>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260402231031.447597-3-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index e15367373f7c..e8aa9cc4075d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2561,7 +2561,14 @@ struct net_device {
 	 * Also protects some fields in:
 	 *	struct napi_struct, struct netdev_queue, struct netdev_rx_queue
 	 *
-	 * Ordering: take after rtnl_lock.
+	 * Ordering:
+	 *
+	 * - take after rtnl_lock
+	 *
+	 * - for the case of netdev queue leasing, the netdev-scope lock is
+	 *   taken for both the virtual and the physical device; to prevent
+	 *   deadlocks, the virtual device's lock must always be acquired
+	 *   before the physical device's (see netdev_nl_queue_create_doit)
 	 */
 	struct mutex		lock;