write_sccb
sccb->header.length = len - offsetof(struct write_sccb, header);
msg->header.length = len - offsetof(struct write_sccb, msg.header);
mdb->header.length = len - offsetof(struct write_sccb, msg.mdb.header);
struct write_sccb *sccb;
sccb = (struct write_sccb *) sclp_early_sccb;