taglinefilesource code
_IO46include/asm-alpha/ioctl.h#define _IO(type,nr)    _IOC(_IOC_NONE,(type),(nr),0)
_IO40include/linux/ioctl.h#define _IO(c,d)  (IOC_VOID | ((c)<<8) | (d)) /* param encoded */
_IO82include/linux/soundcard.h#define  _IO(x,y)  ((int)(IOC_VOID|(x<<8)|y))