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This article introduces the knowledge of "how to write Linux kernel module HelloWorld". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Preparatory work

Before doing the following, I first prepared a computer and installed a virtual machine, the system is Ubuntu16.04. If it is a development board, then you need to install a cross-compiler, but at present I only complete the loading and unloading of the driver module in the Ubuntu16.04 system of the virtual machine, implementing the simplest kernel module, and through this simplest driver, learn the most basic concepts.

You need to install the corresponding development support first

Yum install kernel-headers kernel-devel gcc glibc gcc-c++-y / etc., autoconfig, make and other tools. What is a kernel module?

A module is code that can be dynamically loaded and unloaded into the kernel according to actual needs. They extend the functionality of the kernel without rebooting the system to load modules and work. For example, one type of module is the device driver, which allows the kernel to access the hardware connected to the system. Without modules, we have to build the entire kernel and add new functionality directly to the kernel image. In addition to having a larger kernel, another drawback is that every time we want new functionality, we need to recompile the kernel and burn it to the device.

Writing hello.c#include / / all modules will need this header file # include / / the macro below requires # include / / kernel common library function static int _ _ init hello_init (void) {printk (KERN_INFO "module init success\ n"); return 0;} static void _ exit hello_exit (void) {printk (KERN_INFO "module exit success\ n");} module_init (hello_init); module_exit (hello_exit) MODULE_LICENSE ("GPL"); / / Open Source Protocol MODULE_AUTHOR ("author"); MODULE_DESCRIPTION ("functional description")

This is a simple kernel module program that can be loaded and unloaded dynamically. Although there is no actual function.

Module init success will be printed when the module is loaded\ n

Module exit success will be printed when the module is uninstalled\ n

Module compilation

Makefile

Obj-m: = hello.oPWD: = $(shell pwd) KVER: = $(shell uname-r) KDIR: = / lib/modules/$ (KVER) / build/all: $(MAKE)-C $(KDIR) KDIR $(PWD) clean: rm-rf * .o * .mod.c * .mod.o * .ko * .symvers * .order * .a

After compiling hello.c and Makefile under the same path, hello.ko will be generated under the current path, which is the module we will load into the kernel.

The related instruction namefunctionlsmod looks at the module that has been loaded into the kernel insmod loading module to the kernel rmmod from the kernel unloading module depmod generation module needs to rely on the modprobe very powerful instruction (- h) test result module loading

Load the hello.ko module into the kernel

If the module is loaded successfully, you can view the module

Lsmod | grep hello

A successful load displays the following results

And you can view messages printed by the kernel.

Dmesg | grep "init success" [4160.003247] module init success module uninstalls rmmod hello.ko

After successfully uninstalling the hello module, you can check whether the kernel prints out the print information we preset in the program.

Dmesg | grep "exit success"

You can see that module exit success is displayed on the terminal, indicating that hello.ko was successfully uninstalled through rmmod

[7160.003247] module exit success

At this point, if you look at the current kernel module through lsmod, you will find that hello.ko has disappeared.

This is the end of "how to write Linux kernel module HelloWorld". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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