1 #include <asm/uaccess.h>

2 #include <linux/fs.h>

3 #include <linux/kernel.h>

4 #include <linux/module.h>

5 #include <linux/slab.h>

6

7 #define DEV_NAME "ktest"

8

9 static int ktest_init(void);

10 static void ktest_fini(void);

11

12 static int ktest_open(struct inode *inode, struct file *file);

13 static int ktest_release(struct inode *inode, struct file *file);

14 static ssize_t ktest_read(struct file *file, char *buf, size_t buf_size,

15 loff_t *offset);

16

17 static int dev_num;

18 static struct file_operations ops = {

19 .open = ktest_open,

20 .release = ktest_release,

21 .read = ktest_read

22 };

23 static int hello_counter;

24

25 /* macros */

26

27 MODULE_LICENSE("GPL");

28 MODULE_AUTHOR("hikiko");

29 MODULE_DESCRIPTION("my kernel helloworld");

30

31 module_init(ktest_init);

32 module_exit(ktest_fini);

33

34 static int ktest_init(void)

35 {

36 hello_counter = 0;

37

38 /* register character device */

39 if((dev_num = register_chrdev(0, DEV_NAME, &ops)) < 0) {

40 printk(KERN_ALERT "Failed to register character device.\n");

41 return -1;

42 }

43 printk(KERN_INFO "Registered character device. Name: %s number: %d.\n", DEV_NAME, dev_num);

44 return 0;

45 }

46

47 static void ktest_fini(void)

48 {

49 unregister_chrdev(dev_num, DEV_NAME);

50 printk(KERN_INFO "Unregistered character device. Name: %s number: %d.\n", DEV_NAME, dev_num);

51 }

52

53 static int ktest_open(struct inode *inode, struct file *file)

54 {

55 /* 1 device file only => we ignore the params ^ */

56 try_module_get(THIS_MODULE);

57 return 0;

58 }

59

60 static int ktest_release(struct inode *inode, struct file *file)

61 {

62 module_put(THIS_MODULE);

63 return 0;

64 }

65

66 static ssize_t ktest_read(struct file *file, char *buf, size_t buf_size,

67 loff_t *offset)

68 {

69 /* buf = userspace buffer,

70 * kbuf = kernel buffer */

71

72 char *kbuf;

73 int bytes;

74

75 if(!(kbuf = kmalloc(buf_size, GFP_KERNEL))) {

76 printk(KERN_ALERT "Failed to allocate memory.\n");

77 return -ENOMEM;

78 }

79

80 /* fill kbuf and copy to userspace buf */

81 bytes = snprintf(kbuf, buf_size, "Hello world, num: %d.\n", ++hello_counter);

82

83 if(copy_to_user(buf, kbuf, bytes))

84 {

85 kfree(kbuf);

86 return -EFAULT;

87 }

88

89 kfree(kbuf);

90 return bytes;

91 }