关于ioctl的cmd值如何解析...

遇到ioctl内核中未定义,

打印log

[  739.108300] No such IOCTL, cmd is -1071625723

cmd is -1071625723

这个cmd如何解释呢...?

ioctl原型

SYNOPSIS
#include <sys/ioctl.h>

int ioctl(int d, int request, ...);

其中request/cmd是一个32位整数。

那这个整数是如何定义的呢??

可参考内核文档

./Documentation/ioctl/ioctl-decoding.txt

./Documentation/ioctl/ioctl-number.txt

以上cmd数字的解析规则:

  1 To decode a hex IOCTL code:                                                                                 
  2                                                                                                             
  3 Most architectures use this generic format, but check                                                       
  4 include/ARCH/ioctl.h for specifics, e.g. powerpc                                                            
  5 uses 3 bits to encode read/write and 13 bits for size.                                                      
  6                                                                                                             
  7  bits    meaning                                                                                            
  8  31-30› 00 - no parameters: uses _IO macro                                                                  
  9 ›   10 - read: _IOR                                                                                         
 10 ›   01 - write: _IOW                                                                                        
 11 ›   11 - read/write: _IOWR                                                                                  
 12                                                                                                             
 13  29-16› size of arguments                                                                                   
 14                                                                                                             
 15  15-8›  ascii character supposedly                                                                          
 16 ›   unique to each driver                                                                                   
 17                                                                                                             
 18  7-0›   function #                                                                                          
 19                                                                                                             
 20                                                                                                             
 21 So for example 0x82187201 is a read with arg length of 0x218,                                               
 22 character 'r' function 1. Grepping the source reveals this is:                                              
 23                                                                                                             
 24 #define VFAT_IOCTL_READDIR_BOTH         _IOR('r', 1, struct dirent [2])

-1071625723

写个程序转换成16进制无符号数。

为c0204a05

根据以上规则, bits的含义:

31-30 - 11 读写

29-16 - 长度为0x020 即32byte

15-8 - magic number 魔法数字 - 0x4a

查看ascii码, 为"J"

7-0 - function number 具体的函数对应数字 - 0x5

对应内核代码, 就知道报错原因了...

来源：CSDN

作者：nwpu053883

链接：https://blog.csdn.net/nwpu053883/article/details/103742496

标签

ioctl