vfio_user_config_read
ret = vfio_user_config_read(pdev, pos, &phys_val, count);
ret = vfio_user_config_read(pdev, pos, &phys_val, count);
ret = vfio_user_config_read(vdev->pdev, pos, val, count);
ret = vfio_user_config_read(vdev->pdev, pos, val, count);