On Wed, 30 Sep 2020 22:07:06 +0100 Tom Parkin wrote:

The AC/PPPoE driver implements pseudowire type L2TP_PWTYPE_PPP_AC, for
use in a PPPoE Access Concentrator configuration.  Rather than
terminating the PPP session locally, the AC/PPPoE driver forwards PPP
packets over an L2TP tunnel for termination at the LNS.

l2tp_ac_pppoe provides a data path for PPPoE session packets, and
should be instantiated once a userspace process has completed the PPPoE
discovery process.

To create an instance of an L2TP_PWTYPE_PPP_AC pseudowire, userspace
must use the L2TP_CMD_SESSION_CREATE netlink command, and pass the
following attributes:

 * L2TP_ATTR_IFNAME, to specify the name of the interface associated
   with the PPPoE session;
 * L2TP_ATTR_PPPOE_SESSION_ID, to specify the PPPoE session ID assigned
   to the session;
 * L2TP_ATTR_PPPOE_PEER_MAC_ADDR, to specify the MAC address of the
   PPPoE peer

C=1 generates:

net/l2tp/l2tp_ac_pppoe.c:234:20: warning: incorrect type in argument 1 (different address spaces)
net/l2tp/l2tp_ac_pppoe.c:234:20:    expected struct net_device *dev
net/l2tp/l2tp_ac_pppoe.c:234:20:    got struct net_device [noderef] __rcu *dev
net/l2tp/l2tp_ac_pppoe.c:380:45: error: incompatible types in comparison expression (different address spaces):
net/l2tp/l2tp_ac_pppoe.c:380:45:    struct net_device [noderef] __rcu *
net/l2tp/l2tp_ac_pppoe.c:380:45:    struct net_device *