Lesson3: Implement Linux kernel module

03_module/Makefile

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+obj-m += mymodule.o
+
+# Build for current kernel
+
+#all:
+#	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+#clean:
+#	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+
+
+# Build for another kernel
+
+all:
+	make -C /home/user/Files_Slava/GL_dev/C/linux-kernel/buildroot-2021.02.9/output/build/linux-5.10.7/ M=$(PWD) modules
+
+clean:
+	make -C /home/user/Files_Slava/GL_dev/C/linux-kernel/buildroot-2021.02.9/output/build/linux-5.10.7/ M=$(PWD) clean

03_module/mymodule.c

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+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+static const char* module_name = "mymodule";
+static int a = 0;
+static int b = 0;
+module_param(a, int, 0);
+module_param(b, int, 0);
+
+static int __init hello_init(void)
+{
+	printk(KERN_INFO "%s: Hello world!\n", module_name);
+	printk("%s: a = %i\n", module_name, a);
+	printk("%s: b = %i\n", module_name, b);
+	printk("%s: a + b = %i\n", module_name, a+b);
+	return 0;
+}
+
+static void __exit hello_exit(void)
+{
+	printk(KERN_INFO "%s: Goodbye, world!\n", module_name);
+	printk("%s: a - b = %i\n", module_name, a-b);
+}
+
+module_init(hello_init);
+module_exit(hello_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("ViacheslavHolubnychyi");
+MODULE_DESCRIPTION("simple description");
+MODULE_VERSION("0.1");
+
+MODULE_INFO(intree, "Y");

03_module/result_kernel_log.txt

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+Welcome to Buildroot
+buildroot login: user
+Password: 
+$ pwd
+/home/user
+$ ls
+mymodule.ko
+$ su
+$ insmod mymodule.ko
+mymodule: Hello world!
+mymodule: a = 0
+mymodule: b = 0
+mymodule: a + b = 0
+$ rmmod mymodule
+mymodule: Goodbye, world!
+mymodule: a - b = 0
+$ insmod mymodule.ko a=2
+mymodule: Hello world!
+mymodule: a = 2
+mymodule: b = 0
+mymodule: a + b = 2
+$ rmmod mymodule
+mymodule: Goodbye, world!
+mymodule: a - b = 2
+$ insmod mymodule.ko a=7 b=4
+mymodule: Hello world!
+mymodule: a = 7
+mymodule: b = 4
+mymodule: a + b = 11
+$ rmmod mymodule
+mymodule: Goodbye, world!
+mymodule: a - b = 3
+$ 
+