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 ||       (cmd >= SIOCDEVPRIVATE &&        cmd <= SIOCDEVPRIVATE + 15)) {    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;

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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),