sr_scsi_wu_get
wu_r = sr_scsi_wu_get(sd, 0);
wu_w = sr_scsi_wu_get(sd, 0);
if ((wu_r = sr_scsi_wu_get(sd, SCSI_NOSLEEP)) == NULL){
wu_w = sr_scsi_wu_get(sd, 0);
wu_r = sr_scsi_wu_get(sd, 0);
wu_w = sr_scsi_wu_get(sd, 0);
wu_r = sr_scsi_wu_get(sd, 0);
if ((wu_r = sr_scsi_wu_get(sd, SCSI_NOSLEEP)) == NULL){
struct sr_workunit *sr_scsi_wu_get(struct sr_discipline *, int);