Linux character driver skeleton

Driver file:

1. /*
2. * Simplechrdriver. c
3. *
4. * Copyright (c) 2008 breathomn <breathomn@sohu.com>
5. *
6. */
7. # Include <Linux/module. h>
8. # Include <Linux/kernel. h>
9. # Include <Linux/fs. h>
10. # Include <Linux/init. h>
11. # Include <ASM/uaccess. h>/* Copy _ * _ User */
13. StaticUnsigned int major_num = 0;
15. StaticInt global_var = 0;
17. StaticSsize_t simplechr_read (struct file * filp, char * Buf, ssize_t size, loff_t * Off)
18. {
19. If (copy_to_user (buf, & global_var, sizeof (int )))
20. Return-EFAULT;
21. Return sizeof (int );
22. }
24. StaticSsize_t simplechr_write (struct file * filp, const char * buf, ssize_t size, loff_t * off)
25. {
26. If (copy_from_user (& global_var, buf, sizeof (int )))
27. Return-EFAULT;
28. Return sizeof (int );
29. }
31. StaticStruct file_operations simplechrdev_ops =
32. {
33. . Owner = THIS_MODULE,
34. . Read = simplechr_read,
35. . Write = simplechr_write,
36. };
39. StaticInt _ init simplechr_init (void)
40. {
41. Int ret;
42. If (ret = register_chrdev (major_num, "simplechrdev", & simplechrdev_ops) <0)
43. Printk (KERN_ALERT "simplechrdev register failed! /N ");
44. Else
45. {
46. Major_num = ret;
47. Printk (KERN_ALERT "simplechrdev register success! /N ");
48. }
49. Return ret;
50. }
52. StaticVoid _ exit simplechr_exit (void)
53. {
54. Int ret;
55. If (ret = unregister_chrdev (major_num, "simplechrdev ")))
56. Printk (kern_alert "simplechrdev unregister failed! /N ");
57. Else
58. Printk (kern_alert "simplechrdev unregister success! /N ");
59. }
61. Module_init (simplechr_init );
62. Module_exit (simplechr_exit );

User File:

1. /*
2. * Simplechrsrc. c
3. *
4. * Copyright (c) 2008 breathomn <breathomn@sohu.com>
5. *
6. */
7. # Include <sys/types. h>
8. # Include <sys/stat. h>
9. # Include <stdio. h>
10. # Include <fcntl. h>
12. IntMain ()
13. {
14. Int fd, num;
15. If (fd = open ("/dev/simplechrdev", O_RDWR, S_IRUSR | S_IWUSR ))! =-1)
16. {
17. Read (fd, & num, sizeof (int ));
18. Printf ("Read: % d/n", num );
20. Printf ("Write a num :");
21. Scanf ("% d", & num );
22. Write (FD, & num, sizeof (INT ));
24. Read (FD, & num, sizeof (INT ));
25. Printf ("RAED again: % d/N", num );
27. Close (FD );
28. }
29. Else
30. Printf ("open device failed! /N ");
31. }

MAKEFILE file:

 

OBJ-M: = simplechrdriver. o

Kerneldir? =/Lib/modules/$ (shell uname-R)/build

PWD: = $ (shell PWD)

ALL:
$ (Make)-C $ (kerneldir) M = $ (PWD)

Clean:
Rm-RF *. O *~ Core. depend. *. CMD *. Ko *. Mod. C. tmp_versions

 

Compile our driver into kernel:
(1) create a new directory named simplechrdev in "$ (kernelsource)/Drivers/char" directory.
(2) copy the driver file "simplechrdriver. c" to the new directory.
(3) create a kconfig file in "simplechrdev" directory with contents below:
Config simplechrdev
Tristate "simplechrdev"
(4) modify the kconfig file of its parent directory "char", add contents:
Source "Drivers/Char/simplechrdev/kconfig"
Then we can find a item named "simplechrdev" in "Device Driver-> character devices" when we use "make menuconfig/xconfig ".
(5) create a MAKEFILE file in "simplechrdev" directory with contents below:
OBJ-$ (config_simplechrdev) + = simplechrdriver. o
(6) modify the MAKEFILE file of its parent directory "char", add contents:
OBJ-$ (config_simplechrdev) + = simplechrdev/
All things done! Remake kernel and reboot computer, the driver simplechrdriver works probably. input the command "cat/proc/devices", our device simplechrdev is in the character devices list.
(7) To load our module automatically
We can choose to compile our driver as a module, but sometimes the kernel can not load our module automatically. we can find a solution that add some contents to "/etc/rc. d/RC. sysinit "file to the problem.
# Simplechrdev
If [-D/lib/modules/$ unamer/kernel/Drivers/Char/simplechrdev]; then
For module in/lib/modules/$ unamer/kernel/Drivers/Char/simplechrdev/*; do
Module =$ {module ##*/}
Module =$ {module %. Ko}
Modprobe $ module>/dev/null 2> & 1
Done
Fi