IOCTL的I/O控制疑問

onlyff608

_IOR(base, command, size)

/*
* _IOR means that we're creating an ioctl command
* number for passing information from a user process
* to the kernel module.
*
* The first arguments, MAJOR_NUM, is the major device
* number we're using.
*
* The second argument is the number of the command
* (there could be several with different meanings).
*
* The third argument is the type we want to get from
* the process to the kernel.
*/
沒看懂第二個(gè)參數(shù)是什么意思��？有大牛了解嗎？

steven_miao

以_IOR('V',  0, struct v4l2_capability)為例，第一個(gè)參數(shù)是幻數(shù)，第二個(gè)就是命令，第三個(gè)是傳替參數(shù)的大小。第二個(gè)參數(shù)根據(jù)不同的命令可以定義為任意數(shù)字，這個(gè)就看個(gè)人喜好了。比如：
#define cmdA   _IOR('V',0,struct v4l2_capability)
#define cmdB   _IOR('V',1,struct v4l2_capability)
#define cmdC   _IOR('V',2,struct v4l2_capability)
#define cmdD   _IOR('V',3,struct v4l2_capability)

cluter

The second argument is the number of the command      
第二個(gè)參數(shù) 不就是命令號(hào)么？