net: add ndo_fcoe_ddp_target() to support FCoE DDP in target mode

The Fiber Channel over Ethernet (FCoE) Direct Data Placement (DDP) can also be
used for FCoE target, where the DDP used for read I/O on an initiator can be
used on an FCoE target to speed up the write I/O to the target from the initiator.
The added ndo_fcoe_ddp_target() works in the similar way as the existing
ndo_fcoe_ddp_setup() to allow the underlying hardware set up the DDP context
accordingly when it gets called from the FCoE target implementation on top
the existing Open-FCoE fcoe/libfc protocol stack so without losing the ability
to provide DDP for read I/O as an initiator, it can also provide DDP offload
to the write I/O coming from the initiator as a target.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Kiran Patil <kiran.patil@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

include/linux/netdevice.h

@@ -871,6 +871,10 @@ struct net_device_ops {
 						      unsigned int sgc);
 	int			(*ndo_fcoe_ddp_done)(struct net_device *dev,
 						     u16 xid);
+	int			(*ndo_fcoe_ddp_target)(struct net_device *dev,
+						       u16 xid,
+						       struct scatterlist *sgl,
+						       unsigned int sgc);
 #define NETDEV_FCOE_WWNN 0
 #define NETDEV_FCOE_WWPN 1
 	int			(*ndo_fcoe_get_wwn)(struct net_device *dev,