==============================Decoding an IOCTL Magic Number============================== To decode a hex IOCTL code: Most architectures use this generic format, but checkinclude/ARCH/ioctl.h for specifics, e.g. powerpcuses 3 bits to encode read/write and 13 bits for size.  ====== ================================== bits   meaning ====== ================================== 31-30	00 - no parameters: uses _IO macro	10 - read: _IOR	01 - write: _IOW	11 - read/write: _IOWR  29-16	size of arguments  15-8	ascii character supposedly	unique to each driver  7-0	function # ====== ==================================  So for example 0x82187201 is a read with arg length of 0x218,character 'r' function 1. Grepping the source reveals this is:: 	#define VFAT_IOCTL_READDIR_BOTH         _IOR('r', 1, struct dirent [2])