hello_kmod.c Source

1	// SPDX-License-Identifier: GPL-2.0
2	/*
3	* Minimal Linux kernel module example.
4	*
5	* This module creates /dev/hello_kmod. Reading from it returns a short
6	* message. It is intentionally small so the basic driver shape is visible.
7	*/
8
9	#include <linux/device.h>
10	#include <linux/fs.h>
11	#include <linux/init.h>
12	#include <linux/module.h>
13	#include <linux/uaccess.h>
14
15	#define DEVICE_NAME "hello_kmod"
16	#define CLASS_NAME "hello_class"
17
18	static int major_number;
19	static struct class *hello_class;
20	static struct device *hello_device;
21	static const char message[] = "hello from a tiny kernel driver\n";
22
23	static int hello_open(struct inode *inode, struct file *file)
24	{
25	pr_info("hello_kmod: device opened\n");
26	return 0;
27	}
28
29	static int hello_release(struct inode *inode, struct file *file)
30	{
31	pr_info("hello_kmod: device closed\n");
32	return 0;
33	}
34
35	static ssize_t hello_read(struct file *file, char __user *buffer,
36	size_t length, loff_t *offset)
37	{
38	size_t message_len = sizeof(message) - 1;
39	size_t bytes_to_copy;
40
41	if (*offset >= message_len)
42	return 0;
43
44	bytes_to_copy = min(length, message_len - (size_t)*offset);
45
46	if (copy_to_user(buffer, message + *offset, bytes_to_copy))
47	return -EFAULT;
48
49	*offset += bytes_to_copy;
50	return bytes_to_copy;
51	}
52
53	static const struct file_operations hello_fops = {
54	.owner = THIS_MODULE,
55	.open = hello_open,
56	.read = hello_read,
57	.release = hello_release,
58	};
59
60	static int __init hello_init(void)
61	{
62	major_number = register_chrdev(0, DEVICE_NAME, &hello_fops);
63	if (major_number < 0) {
64	pr_err("hello_kmod: failed to register char device\n");
65	return major_number;
66	}
67
68	hello_class = class_create(CLASS_NAME);
69	if (IS_ERR(hello_class)) {
70	unregister_chrdev(major_number, DEVICE_NAME);
71	return PTR_ERR(hello_class);
72	}
73
74	hello_device = device_create(hello_class, NULL, MKDEV(major_number, 0),
75	NULL, DEVICE_NAME);
76	if (IS_ERR(hello_device)) {
77	class_destroy(hello_class);
78	unregister_chrdev(major_number, DEVICE_NAME);
79	return PTR_ERR(hello_device);
80	}
81
82	pr_info("hello_kmod: loaded as /dev/%s with major %d\n",
83	DEVICE_NAME, major_number);
84	return 0;
85	}
86
87	static void __exit hello_exit(void)
88	{
89	device_destroy(hello_class, MKDEV(major_number, 0));
90	class_destroy(hello_class);
91	unregister_chrdev(major_number, DEVICE_NAME);
92	pr_info("hello_kmod: unloaded\n");
93	}
94
95	module_init(hello_init);
96	module_exit(hello_exit);
97
98	MODULE_LICENSE("GPL");
99	MODULE_AUTHOR("Digital Rhyme Knowledge Base");
100	MODULE_DESCRIPTION("Minimal Linux character device kernel module");