linux – 網路設備 ioctl 命令參數範圍：SIOCDEVPRIVATE（0-15）

struct iwreq iwr;
s = socket(AF_INET, SOCK_DGRAM, 0);

ioctl(s, (SIOCDEVPRIVATE+15), &iwr) 正常调用
ioctl(s, (SIOCDEVPRIVATE+16), &iwr) 返回错误，应为内核代码只分配了0-15的空间为用户私有可用的。

见代码：
linux/net/code/dev.c

* Unknown or private ioctl.

default:

if (cmd == SIOCWANDEV ||

<strong> (cmd >= SIOCDEVPRIVATE &&

cmd <= SIOCDEVPRIVATE + 15)</strong>) {

dev_load(net, ifr.ifr_name);

rtnl_lock();

ret = dev_ifsioc(net, &ifr, cmd);

rtnl_unlock();

if (!ret && copy_to_user(arg, &ifr,

sizeof(struct ifreq)))

ret = -EFAULT;

return ret;

}

/* Take care of Wireless Extensions */

if (cmd >= SIOCIWFIRST && cmd <= SIOCIWLAST)

return wext_handle_ioctl(net, &ifr, cmd, arg);

return -EINVAL;

——————————
其中
(cmd >= SIOCDEVPRIVATE && cmd <= SIOCDEVPRIVATE + 15)) 为用户私有，所以在ioctl调用时，只能使用(SIOCDEVPRIVATE+0)到 (SIOCDEVPRIVATE+15),