c-如何检查ioctl上的现有参数

Question

我想尝试如何使用可加载内核模块的I/o控件，这里是一个字符设备。问题是：如何检查用户空间端的ioctl调用是否有参数。我发现在ioctl上，一个参数是可选的。

用户空间功能内部：

// set a parameter - this is a proper call
if( ioctl(fd, IOCTL_SET_PARAM1, 5)<0 )
{
  fprintf(stderr,"Error while ioctl: %sn", strerror(errno));
}
// call a setter without argument - this should cause an error
if( ioctl(fd, IOCTL_SET_PARAM1)<0 )
{
  fprintf(stderr,"Error while ioctl: %sn", strerror(errno));
}

相应的内核模块处理程序：

long
fops_unlocked_ioctl (struct file    *p_file,
                     unsigned int    cmd,
                     unsigned long   arg)
{
  switch(cmd)
  {
  case IOCTL_SET_PARAM1:
    printk(KERN_INFO "IOCTL called with IOCTL_SET_PARAM1n");
    if( /* how to check for the argument here? */ )
    {
      printk(KERN_WARNING "Missing argumentn");
      return -EINVAL;
    }
    param1 = (unsigned short) arg;
    printk(KERN_INFO "param1 set to %dn",param1);
    break;
  default:
    printk(KERN_WARNING "IOCTL called with wrong request code.n");
    return -EINVAL;
  }
  return 0;
}

谨致问候，Alex

Answer 1

Jonathan Leffler完全正确，然后他说，用户应该知道该做什么和不该做什么。

对了。我想出了一个解决方案，用计数和原始参数的数组替换参数。在用户空间方面，用户没有任何变化。在内核空间方面，有两个宏来获取原始参数和参数数量。

代码来了：

expdev.h

#ifndef EXPDEV_H_INCLUDED
#define EXPDEV_H_INCLUDED
#ifndef __KERNEL__
  #include <stdint.h>
#endif // __KERNEL__
#include "pp_narg.h"
enum {
  IOCTL_SET_PARAM1,
};
/* ioctl - wrapper *************************************************** */
#ifndef __KERNEL__
  long int argW[2]={0};
  long int PP_IOCTL_WRAPARG( long int narg, long int arg )
  {
    argW[0] = narg;
    argW[1] = arg;
    return (long int)(argW);
  }
  #define PP_IOCTL_NARG(n,fd,cmd,arg,...) 
    ( (n==3) ? 
      ( ioctl(fd,cmd,(long int)(PP_IOCTL_WRAPARG(1,(long int)arg))) ) : 
      ( ioctl(fd,cmd,(long int)(PP_IOCTL_WRAPARG(0,(long int)arg))) ) )
  #define ioctl(...) 
    (PP_IOCTL_NARG(PP_NARG(__VA_ARGS__),         
                   __VA_ARGS__, (long int)(0),(long int)(0)))
#else // __KERNEL__
  #define IOCTL_ARGC(argW) (((long int*)argW)[0])
  #define IOCTL_ARG(argW)  (((long int*)argW)[1])
#endif // __KERNEL__
#endif // EXPDEV_H_INCLUDED

为了计算论点，我关注这篇文章。

pp_narg.h

/*
 Source: https://groups.google.com/forum/#!topic/comp.std.c/d-6Mj5Lko_s
 */
#ifndef PP_NARG_INCLUDED
#define PP_NARG_INCLUDED
#define PP_NARG(...) 
         PP_NARG_(__VA_ARGS__,PP_RSEQ_N())
#define PP_NARG_(...) 
         PP_ARG_N(__VA_ARGS__)
#define PP_ARG_N( 
          _1, _2, _3, _4, _5, _6, _7, _8, _9,_10, 
         _11,_12,_13,_14,_15,_16,_17,_18,_19,_20, 
         _21,_22,_23,_24,_25,_26,_27,_28,_29,_30, 
         _31,_32,_33,_34,_35,_36,_37,_38,_39,_40, 
         _41,_42,_43,_44,_45,_46,_47,_48,_49,_50, 
         _51,_52,_53,_54,_55,_56,_57,_58,_59,_60, 
         _61,_62,_63,N,...) N
#define PP_RSEQ_N() 
         63,62,61,60,                   
         59,58,57,56,55,54,53,52,51,50, 
         49,48,47,46,45,44,43,42,41,40, 
         39,38,37,36,35,34,33,32,31,30, 
         29,28,27,26,25,24,23,22,21,20, 
         19,18,17,16,15,14,13,12,11,10, 
         9,8,7,6,5,4,3,2,1,0
#endif // PP_NARG_INCLUDED

现在在用户空间函数内调用(和往常一样(：

#include "expdev.h"
// set a parameter
if( ioctl(fd, IOCTL_SET_PARAM1, 5)<0 )
{
  fprintf(stderr,"Error while ioctl: %sn", strerror(errno));
}
// call a setter without argument - this should cause an error
if( ioctl(fd, IOCTL_SET_PARAM1)<0 )
{
  fprintf(stderr,"Error while ioctl: %sn", strerror(errno));
}

内核空间侧(注意IOCTL_ARGC(arg)和IOCTL_ARG(arg)(:

#include "expdev.h"
long
fops_unlocked_ioctl (struct file    *p_file,
                     unsigned int    cmd,
                     unsigned long   arg)
{
  switch(cmd)
  {
  case IOCTL_SET_PARAM1:
    printk(KERN_INFO "IOCTL called with IOCTL_SET_PARAM1n");
    if( IOCTL_ARGC(arg)!=1 )
    {
      printk(KERN_ERR "Missing argument.n");
      return -EINVAL;
    }
    param1 = (unsigned short) IOCTL_ARG(arg);
    printk(KERN_INFO "param1 set to %dn",param1);
    break;
  default:
    printk(KERN_WARNING "IOCTL called with wrong request code.n");
    return -EINVAL;
  }
  return 0;
}

这导致kern.log上的以下输出：

kernel: [18577.042438] IOCTL called with IOCTL_SET_PARAM1
kernel: [18577.042439] param1 set to 5
kernel: [18577.042442] IOCTL called with IOCTL_SET_PARAM1
kernel: [18577.042443] Missing argument.

在用户空间方面：

Error while ioctl: Invalid argument

注意：

宏重新定义了ioctl。这意味着在同一源内的不同设备上使用ioctl会在不支持此宏的设备上导致错误(例如，如果使用标准tty(。