[Acer]_IOC_NR, _ioc_type, _ioc_size, _ioc_dir

From:http://www.groad.net/bbs/read.php?tid-1213.html _ioc_nr (), _ioc_type (), _ioc_size (), _IOC_DIR () These macros are used to get the cmd command domain, which functions as follows:

_ioc_nr (): Reading radix value (bit0~ bit7)

_ioc_type : Read the Magic Number field value (bit8 ~ bit15)

_ioc_size : Reading Data size field value (bit16 ~ bit29)

_ioc_dir : Get read-write property field value (Bit30 ~ bit31)

the _IOC_NR () is defined as :
#define _IOC_NR (NR) ((NR) >> _ioc_nrshift) & _ioc_nrmask)

The value of _ioc_nrshift is 0;

the definition of _ioc_nrmask is :
#define _IOC_NRMASK ((1 << _ioc_nrbits)-1)

The value of the _ioc_nrbits is defined as 8, so the _ioc_nrmask value is 0xFF.

The rest of the macro analysis is similar.