Linux驅動程序設計的時候偶然發現的ioctl()函數的cmd參數不能為2，如果為2,ioctl()函數返回-1，網上說就是這樣的，正常，不知道為什么，stack overflow上有一個外國學友的建議：

“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”