ioc_read_subchannel
struct ioc_read_subchannel *args
= (struct ioc_read_subchannel *) addr;
struct ioc_read_subchannel *args =
(struct ioc_read_subchannel *)ap->a_data;
#define CDIOCREADSUBCHANNEL _IOWR('c', 3 , struct ioc_read_subchannel )
struct ioc_read_subchannel s;
struct ioc_read_subchannel ss;