Linux驱动设计ioctl函数的cmd参数不能为2

Linux驱动程序设计的时候偶然发现的ioctl()函数的cmd参数不能为2，如果为2,ioctl()函数返回-1，网上说就是这样的，正常，不知道为什么，stack
overflow上有一个外国学友的建议：

“In general, you want to compose your ioctl commands
using the 

_IO

 family
of macros, with a unique type, to avoid collisions.

I suggest reading ioctl-number.txt from the kernel documentation for
more information, including a list of most used types”

In general, you want to compose your ioctl commands using the 

_IO

 family
of macros, with a unique type, to avoid collisions.

I suggest reading ioctl-number.txt from the kernel documentation for
more information, including a list of most used types”