seq_event_rec
CTASSERT(sizeof(seq_event_rec) == SEQ_SYSEX_HDRSIZE);
t = SEQ_MAXQ - *(int *)addr / sizeof (seq_event_rec);
kn->kn_data = sizeof(seq_event_rec);
kn->kn_data = sizeof(seq_event_rec);
#define SEQUENCER_OUTOFBAND _IOW ('Q',18, struct seq_event_rec)