One of the notes for Linux Device Driver (Third edition): Use of scull Devices

Note:
Use of scull Devices

By:	Wu Yin
Date:	2007-07-05
Email:	Lazy. Fox. Wu # gmail.com
Homepage:	Http://blog.csdn.net/wooin
Copyright:	This article is copyrighted by Wu Yi. It can be freely transmitted and replicated for non-commercial purposes. For commercial purposes, any behavior in this article shall be approved by the author. Contact info: lazy. Fox. Wu # gmail.com

1.	Preface: A. Before proceeding to the following work, please read my article "compile a kernel module that can be loaded under the Linux 2.6 kernel" to configure a Linux environment that can be loaded with the kernel module B. Download the source code for the Linux Device Driver (Third edition). You can download it here. If you cannot download it, leave a message or send me an email. C. The working environment in this article is Fedora Core 5. Use "uname-R" to check whether the kernel version is 2.6.15-1.2054 _ fc5. D. This article focuses on the Linux Device Driver (version 3) Chapter 3: character Device Driver E. Some of the following operations require the root permission, so try to use the root user to execute the command.
2.	Decompress the source code package and enter the scull folder. The files include: Access. c Main. c The main program, Scull device initialization, uninstallation, open, write, and Other implementations are all in this area. Makefile Pipe. c Chapter 6 "advanced character driver operations" will be used to explain blocking-type backup. Scull. h Header file Scull. init Scull_load Script for loading the scull Module Scull_unload Uninstall the scull module script
3.	Run the make command in the scull directory to compile and run scull. ko file, and then run the script scull_load. If no output is returned, the scull device will automatically load it to the kernel, in this case, you can view the/proc/devices file to find the newly loaded scull module and the master device number assigned to it by the inner core. Many characters starting with scull are added to/dev.
4.	Try scull device: Run the following command: # Ls-L>/dev/scull # No output is returned. # Cat/dev/scull # Run the cat command to read the scull device, and the output information of the above command will be read. Total 900 -RW-1 baobaowu 10845 2005-02-01 access. c -RW-r -- 1 baobaowu 74580 06-15 access. o -RW-1 baobaowu 16631 06-15 main. c -RW-r -- 1 baobaowu 74512 06-15 main. o -RW-r -- 1 baobaowu 752 makefile -RW-1 baobaowu 11138 2005-02-01 pipe. c -RW-r -- 1 baobaowu 71576 06-15 pipe. o -RW-r -- 1 baobaowu 5153 2005-02-01 scull. h -Rwxr-XR-x 1 baobaowu 3309 2005-02-01 scull. init -RW-r -- 1 baobaowu 248556 06-15 scull. Ko -Rwxr-XR-x 1 baobaowu 1708 06-15 scull_load -RW-1 baobaowu 1852 06-15 scull. Mod. c -RW-r -- 1 baobaowu 33696 06-15 scull. Mod. o -RW-r -- 1 baobaowu 216043 06-15 scull. o -Rwxr-XR-x 1 baobaowu 335 2005-02-01 scull_unload Sure enough, the scull device, as described in the book, only exists in a buffer zone in the memory.
5.	Run scull_unload again. No output is returned, but the scull module has been deleted from the kernel, and no scull device exists in the/proc/devices file, /dev/also has no character device that starts with scull.
6.	Some debugging information is added in scull as follows: Open the main. c file and add a sentence to the header of the scull_init_module () function: Printk (kern_alert "Debug by baobaowu: scull_init_module ()/n "); Add the following statement to the header of the scull_read () function: Printk (kern_alert "Debug by baobaowu: scull_read ()/n "); Add the following statement to the header of the scull_write () function: Printk (kern_alert "Debug by baobaowu: scull_write ()/n "); Save and run make to compile.
7.	Repeat Step 1 to load scull into the kernel. At this time, the kernel should call the scull_init_module () function in Main. c. is it called? Let's take a look at the/var/log/messages file. The debugging information is output at the end of the file: Debug by baobaowu: scull_init_module () How can I call read and write? Next we will introduce it below.
8.	As you can imagine, writing data to a device calls the scull_write () function. We execute the following command to write data to the/dev/scull device using the output redirection: # Ls-L>/dev/scull After executing the command, check the/var/log/messages file. The debugging information is displayed at the end of the file: Debug by baobaowu: scull_write ()
9.	The scull_read () function should be called to read data from the device. We use the DD command to read the scull device: # Dd If =/dev/scull of = temp # read data from/dev/scull and save it to the temp file in the current directory After executing the command, check the/var/log/messages file. The debugging information is displayed at the end of the file: Debug by baobaowu: scull_read ()
10.	The scull usage described in this article is helpful for reading the character device driver in Chapter 3 after successful debugging. When you encounter something you don't understand or are not sure about, printk will be fine. ^_^