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Linux Kernel Module Programming

The first is to learn Linux module programming, according to the book's examples the Hello.ko experienced some twists and turns, everything only personally tried, only to know in detail how ah. The following records to complete the preparation of this simple module, load, unload the whole process and must pay attention to.

A hello.c file created in any one place, which wrote the following:

 
 
 
  
  

  
  
  
   
    / * Hello.c * / 
  
  
  
   
      
  
  
  
   
    # Include 
  
  
  
   
     
  
  
  
   
    <linux/init.h> 
  
  
  
   
      
  
  
  
   
    # Include 
  
  
  
   
     
  
  
  
   
    <linux/module.h> MODULE_LICENSE ("Dual BSD / GPL"); 
  
  
  
   
        
  
  
  
   
    static 
  
  
  
   
     
  
  
  
   
    the int hello_init (void) 
  
  
  
   
      
  
  
  
   
    {Printk (KERN_ALERT "Hello, World / n"); 
  
  
  
   
           
  
  
  
   
    return 
  
  
  
   
     
  
  
  
   
    0; 
  
  
  
   
      
  
  
  
   
    } 
  
  
  
   
        
  
  
  
   
    static 
  
  
  
   
     
  
  
  
   
    the int hello_exit (void) 
  
  
  
   
      
  
  
  
   
    {Printk (KERN_ALERT "Goodbye, cruel world / n"); 
  
  
  
   
      
  
  
  
   
    } Module_init (hello_init); module_exit (hello_exit); 
  
  
  
   
     
 
 
 
  
  

This module is to do nothing, just prints a message when the module is loaded, uninstall also prints a message. Though small, but with all MODULE_LICENSE () specified authentication method now supports: "GPL" GPL v2 "GPL and Additional Rights" Dual BSD / GPL "Dual MIT / GPL Dual MPL / GPL "" Proprietary ", which is the kernel 2.6 added, and found that it is not required. specified module_init () module entrance, which is required Home; the module_exit () specified module export, which is required.

Compiler extensions, use make to create a Makefile in the same directory with the hello.c, as follows:

 
 
 
  
  
 
  
  
  
   
    / * Makefile * / 
  
  
  
   
     
  
  
  
   
    TARGET = Hello 
  
  
  
   
     
  
  
  
   
    KDIR = / usr / src / linux - headers - 2.6. 31 - 19 - generic 
  
  
  
   
     
  
  
  
   
    PWD = $ (shell pwd) 
  
  
  
   
     
  
  
  
   
    obj - m: = $ (TARGET). o 
  
  
  
   
     
  
  
  
   
    default: 
  
  
  
   
     
  
  
  
   
    make - C $ (KDIR) M = $ (PWD) modules 
  
  
  
   
     
 
 
 
  
  

Indicates the name of the target file, which target KDIR pointed out the reference to the location of the header files, modify the file, depending on the circumstances. There are several things to note, the module compiler needs to have a kernel source directory structure, if there is a kernel source is certainly better, directly change KDIR to the source path on OK. Of course, there is only one kernel directory structure will be, after all, just need the header files, and build scripts, there is such a directory structure in Linux release the / usr / src / under like my system Ubuntu9. 10, the kernel 2.6.31-19 generic version in / usr / src / under there linux-headers-2.6.31-19-generic such a directory. So I use KDIR = / usr/src/linux-headers-2.6.31-19-generic. In fact, there is a directory called linux-headers-2.6.31-19, and you will find that most of the files are just the linux-headers-2.6.31-19-generic linux-headers-2.6.31-19 some point link, but the default linux-headers-2.6.31-19 inside the compiled module file is missing, do not use it.

Next, as long as you use the make command, you can compile and make for you everything, it will according to KDIR find compile the required documentation. If your luck is good, your current directory will mature hello.o hello.mod.o hello.mod.c modules.order Module.markers Module.symvers hello.ko, of course, cute is what we want to hello.ko want. This module has been successfully generated, the next will be able to load the module to see the effect.

Use the insmod. / Hello.ko to load the module, if you encounter insmod: error inserting 'hello.o':-l invalid module format this error, do not panic, not your module, but you are currently running The kernel version is inconsistent with the first version of the file that you compile and link, so there will be the problem of the wrong format. At this point, you can replace the system kernel, recompile the module can also download a system version of the kernel source. If you do not encounter any problems, did not print out any information, then congratulations, your kernel loaded successfully, you can use the lsmod command to list all the modules loaded your system, I believe you will find in the list hello. You may be wondering, why did not as we think of it, print out "Hello, World"? Oh, this is because the the printk will not print the contents of the print to the terminal you face to face, to know the module is running in kernel mode, you can face the user mode, kernel mode print information need to log or dmesg command to see, want to see the print results, the easiest way is typing dmesg command, you can see the information you want to see, you can open this file in / var / log / message view .

Finally, to use rmmod hello to uninstall module, the same, using the dmesg you can see the print out "Goodbye, cruel world".