iwpriv配置失败的问题追踪[ioctl调用过程解析]

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本文分析了在执行iwpriv配置时遇到的ioctl错误问题。通过跟踪从用户空间到内核空间的ioctl调用流程，发现错误源于在app中iw_get_ext()函数分配的空间不足，导致在net/wireless/wext-priv.c中的iw_handler_get_private判断失败。

现象：执行 iwpriv athXXX XXXX , ioctl报错

bugfix：

【 app 】 [ iwpriv.c] print_priv_info ---> [iwlib.c] iw_get_priv_info ---> iw_get_ext(skfd, ifname, SIOCGIWPRIV, &wrq) ---> ioctl(skfd, request, pwrq)

【kernel】上述ioctl实际上通过系统调用进入kernel space,

fs/Ioctl.c

SYSCALL_DEFINE3(ioctl, unsigned int, fd,unsigned int, cmd, unsigned long, arg)

{

……………………………………………………………………..

error= do_vfs_ioctl(filp, fd, cmd, arg);//调用虚拟文件系统的ioctl

……………………………………………………………..

}

do_vfs_ioctl ---> vfs_ioctl(filp, cmd, arg) ---> filp->f_op->unlocked_ioctl(filp, cmd, arg)

net/socket.c

static const struct file_operations socket_file_ops = {
   .owner =   THIS_MODULE,
   .llseek =   no_llseek,
   .aio_read =   sock_aio_read,
   .aio_write =   sock_aio_write,
   .poll =       sock_poll,
   .unlocked_ioctl = sock_ioctl,
#ifdef CONFIG_COMPAT
   .compat_ioctl = compat_sock_ioctl,
#endif
   .mmap =       sock_mmap,
   .open =       sock_no_open,   /* special open code to disallow open via /proc */
   .release =   sock_close,
   .fasync =   sock_fasync,
   .sendpage =   sock_sendpage,
   .splice_write = generic_splice_sendpage,
   .splice_read =   sock_splice_read,
};
              static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)

..............

             #ifdef CONFIG_WEXT_CORE
      if (cmd >= SIOCIWFIRST && cmd <= SIOCIWLAST) {
             err = dev_ioctl(net, cmd, argp);
      } else
             #endif

net/core/dev.c
dev_ioctl ---> [net/wireless/wext-core.c] wext_handle_ioctl ---> wext_ioctl_dispatch ---> [net/wireless/wext-priv.c] iw_handler_get_private

if (wrqu->data.length < dev->wireless_handlers->num_private_args)

..........

追踪发现这里判断失败导致问题，向上追其根源：app中 iw_get_ext(skfd, ifname, SIOCGIWPRIV, &wrq) 分配的空间不足导致的问题