Linux ioctl command

Excepted from kernel/include/asm-generic/ioctl.h

 

/* ioctl command encoding: 32 bits total, command in lower 16 bits,
 * size of the parameter structure in the lower 14 bits of the
 * upper 16 bits.
 * Encoding the size of the parameter structure in the ioctl request
 * is useful for catching programs compiled with old versions
 * and to avoid overwriting user space outside the user buffer area.
 * The highest 2 bits are reserved for indicating the ``access mode''.
 * NOTE: This limits the max parameter size to 16kB -1 !
 */

/*
 * The following is for compatibility across the various Linux
 * platforms.  The generic ioctl numbering scheme doesn't really enforce
 * a type field.  De facto, however, the top 8 bits of the lower 16
 * bits are indeed used as a type field, so we might just as well make
 * this explicit here.  Please be sure to use the decoding macros
 * below from now on.
 */

 

ioctl 命令对32-bit 字长进行编码。

最高两位 bit 31:30 定义为存取模式 (access mode)

14-bit （Bit 29:16）定义为ioctl请求的参数结构体。 根据14-bit 长度，最大参数结构体大小为16KB -1。

最低16bit (Bit 15:0) 定义为 ioctl 命令。

 

#define _IOC_NRBITS8#define _IOC_TYPEBITS8/* * Let any architecture override either of the following before * including this file. */#ifndef _IOC_SIZEBITS# define _IOC_SIZEBITS14#endif#ifndef _IOC_DIRBITS# define _IOC_DIRBITS2#endif#define _IOC_NRMASK((1 << _IOC_NRBITS)-1)#define _IOC_TYPEMASK((1 << _IOC_TYPEBITS)-1)#define _IOC_SIZEMASK((1 << _IOC_SIZEBITS)-1)#define _IOC_DIRMASK((1 << _IOC_DIRBITS)-1)#define _IOC_NRSHIFT0#define _IOC_TYPESHIFT(_IOC_NRSHIFT+_IOC_NRBITS)#define _IOC_SIZESHIFT(_IOC_TYPESHIFT+_IOC_TYPEBITS)#define _IOC_DIRSHIFT(_IOC_SIZESHIFT+_IOC_SIZEBITS)/* * Direction bits, which any architecture can choose to override * before including this file. */#ifndef _IOC_NONE# define _IOC_NONE0U#endif#ifndef _IOC_WRITE# define _IOC_WRITE1U#endif#ifndef _IOC_READ# define _IOC_READ2U#endif#define _IOC(dir,type,nr,size) \(((dir)  << _IOC_DIRSHIFT) | \ ((type) << _IOC_TYPESHIFT) | \ ((nr)   << _IOC_NRSHIFT) | \ ((size) << _IOC_SIZESHIFT))#ifdef __KERNEL__/* provoke compile error for invalid uses of size argument */extern unsigned int __invalid_size_argument_for_IOC;#define _IOC_TYPECHECK(t) \((sizeof(t) == sizeof(t[1]) && \  sizeof(t) < (1 << _IOC_SIZEBITS)) ? \  sizeof(t) : __invalid_size_argument_for_IOC)#else#define _IOC_TYPECHECK(t) (sizeof(t))#endif/* used to create numbers */#define _IO(type,nr)_IOC(_IOC_NONE,(type),(nr),0)#define _IOR(type,nr,size)_IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size)))#define _IOW(type,nr,size)_IOC(_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))#define _IOWR(type,nr,size)_IOC(_IOC_READ|_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))#define _IOR_BAD(type,nr,size)_IOC(_IOC_READ,(type),(nr),sizeof(size))#define _IOW_BAD(type,nr,size)_IOC(_IOC_WRITE,(type),(nr),sizeof(size))#define _IOWR_BAD(type,nr,size)_IOC(_IOC_READ|_IOC_WRITE,(type),(nr),sizeof(size))/* used to decode ioctl numbers.. */#define _IOC_DIR(nr)(((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK)#define _IOC_TYPE(nr)(((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)#define _IOC_NR(nr)(((nr) >> _IOC_NRSHIFT) & _IOC_NRMASK)#define _IOC_SIZE(nr)(((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)/* ...and for the drivers/sound files... */#define IOC_IN(_IOC_WRITE << _IOC_DIRSHIFT)#define IOC_OUT(_IOC_READ << _IOC_DIRSHIFT)#define IOC_INOUT((_IOC_WRITE|_IOC_READ) << _IOC_DIRSHIFT)#define IOCSIZE_MASK(_IOC_SIZEMASK << _IOC_SIZESHIFT)#define IOCSIZE_SHIFT(_IOC_SIZESHIFT)