step

Adding modules to the kernel

1. Write Driver
2. Add drivers to the linux source directory, typically inside / Drivers
3. Add the project compilation option corresponding to the driver in the Kconfig file where the directory is located
4. Add compilation statements for new drivers to the Makefile file file in the directory

Test Dynamic Add Module

• Files to be written are test.c add_sub.h add_sub.c and Makefile under test.c and add_sub.c

//test.c
/*************************************************************************
    > File Name: test.c
    > Author: houwenzhi
    > Mail: houwenzhi@163.com 
    > Created Time: 2020 Friday, March 13, 2003, 10:41 min 16 seconds
 ************************************************************************/
#include <linux/init.h>
#include <linux/module.h>
#include "add_sub.h"
#include <linux/kernel.h>
static long a = 1;
static long b = 1;
static int AddOrSub = 1;

static int test_init(void)
{
    long result = 0;
    printk("test initi\r\n");
    if(1 == AddOrSub)
    {
        result = add_integer(a,b);
    }
    else
    {
        result = sub_integer(a,b);
    }
    printk("The %s result is %ld",AddOrSub==1?"Add":"Sub",result);
    return 0;
}
static void test_exit(void)
{
    printk("test exit\r\n");
}

module_param(a,long,S_IRUGO);
module_param(b,long,S_IRUGO);
module_param(AddOrSub,int,S_IRUGO);
module_init(test_init);
module_exit(test_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("HouWenzhi");

#Makefile
obj-m :=test.o
    KERNELDIR ?= /home/user/source/linux-2.6.30

    PWD := $(shell pwd)
    SYMBOL_INC = $(obj)/../$(SYMBOL_INC)
    KBUILD_EXTRA_SYMBOLS=$(obj)/../print/Module.symvers
    
modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
    rm -rf *.o *~core .depend .*.cmd *.ko *.mod.c .tmp_versions
.PHONY:modules modules_install clean

//add_sub.c
/*************************************************************************
    > File Name: add_sub.c
    > Author: houwenzhi
    > Mail: houwenzhi@163.com 
    > Created Time: 2020 Friday, March 13, 2003, 11:24 min 59 seconds
 ************************************************************************/

#include <linux/module.h>
#include <linux/init.h>
#include "../add_sub.h"

long  add_integer(int a,int b)
{
    return a + b;
}
long sub_integer(int a,int b)
{
    return a - b;
}
EXPORT_SYMBOL(add_integer);
EXPORT_SYMBOL(sub_integer);
MODULE_LICENSE("GPL");

#Makefile
ifeq ($(KERNELRELEASE),)
    KERNELDIR ?= /home/user/source/linux-2.6.30
    PWD := $(shell pwd)
    PRINT_INC = $(PWD)/../include
    EXTRA_CFLAGS += -I $(PRINT_INC)
modules:
    $(MAKE) -I $(PRINT_INC) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
    rm -rf *.o *~core .depend .*.cmd *.ko *.mod.c .tmp_versions
.PHONY:modules modules_install clean
else
    obj-m :=add_sub.o
endif

/*************************************************************************
    > File Name: add_sub.h
    > Author: houwenzhi
    > Mail: houwenzhi@163.com 
    > Created Time: 2020 Friday, March 13, 2003, 11:19 min 15 seconds
 ************************************************************************/

#ifndef _ADD_SUB_H_
#define _ADD_SUB_H_

long add_integer(int a,int b);
long sub_integer(int a,int b);

#endif

1. The example above describes the communication between modules through two modules, which add_subt provides two export functions, add_integer(), and sub_integer(), that add and subtract two numbers, respectively.The module test calls two methods of the module's add_subto complete an addition or subtraction operation.
2. Test module
   Before loading the test module, the add_submodule needs to be loaded before the test module can access the export functions of the add_submodule body
   insmod add_sub.ko
   insmod test.ko a=3 b=2 AddOrSub=2
   • This is a dynamic loading method

Add modules to the kernel

• First, the directory of the kernel module is in the / dervers directory, under which a new directory is created, add_sub_Config
  Include in Catalog

$:cd add_sub_Config
$:tree
.
├── add_sub.c
├── add_sub.h
├── Kconfig
├── Makefile
└── test.c

1. Modify Kconfig

menu "ADD_SUB"
    comment "ADD_SUB"
config CONFIG_ADD_SUB
    boolean "ADD_SUB support"
    default y
config CONFIG_TEST
    tristate "ADD_SUB test support"
    depends on CONFIG_ADD_SUB
    default y
endmenu

1. Modify Makefile

obj-$(CONFIG_ADD_SUB) +=add_sub.o
obj-$(CONFIG_TEST) +=test.o

3. Modify the Kconfig of the upper directory, add

source "drivers/add_sub_Kconfig/Kconfig"

1. Modify the Makefile in the upper directory, add
   obj-$(ADD_SUB) += add_sub_Kconfig/

Configuring the add_sub module

$:make menuconfig
The Add_Sub module is theoretically found in the Device Drivers directory, but there is no such module. After repeated experimentation, no results are found and recorded