ixgbe: Do not return 0 in ixgbe_fcoe_ddp() upon FCP_RSP in DDP completion

We return the ddp->len in ixgbe_fcoe_ddp() to indicate the length of data that
have been DDPed. However, it is possible that the length is 0, e.g., for SCSI
READ, the FCP_RSP may come back w/ SCSI status 0x28 as Task Set Full with no FCP
data for DDP. In ixgbe_fcoe_ddp(), we return 0 to indicate not passing DDPed
packets to upper layer. Therefore in the case of ddp->len being 0 upon FCP_RSP,
we do not want to return the 0 ddp->len as we want FCP_RSP to be always
delivered to the upper layer. This patch fixes this bug by setting rc only if
ddp->len is non-zero.
Signed-off-by: NYi Zou <yi.zou@intel.com>
Acked-by: NPeter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_fcoe.c

@@ -336,7 +336,7 @@ int ixgbe_fcoe_ddp(struct ixgbe_adapter *adapter,
 		/* return 0 to bypass going to ULD for DDPed data */
 		if (fcstat == IXGBE_RXDADV_STAT_FCSTAT_DDP)
 			rc = 0;
-		else
+		else if (ddp->len)
 			rc = ddp->len;
 	}