844beed5d7
Change the "alloc_ret" and "cdev_ret" initial values to non-zero. According to the source code, "alloc_chrdev_region" and "cdev_add" return zero on success, and negative code on failure. So, if the "alloc_chrdev_region" failed, the if condition becomes true, then we will jump to the label "error" by goto, checking each return value whether is a success state from both functions mentioned above and dealing with it properly for exiting the process. However, it checks the success state by comparing the return value with zero (means success), and we got "cdev_ret == 0" is true from the initial value zero, while we didn't execute "cdev_add" yet. Hence, there was a logic error when the initial value is zero. Co-authored-by: NOVBobLee <defru04002@gamil.com>
The Linux Kernel Module Programming Guide
This project keeps the Linux Kernel Module Programming Guide up to date, with working examples for recent 5.x kernel versions. The guide has been around since 2001 and most copies of it on the web only describe old 2.6.x kernels.
The book can be freely accessed via https://sysprog21.github.io/lkmpg/ or latest PDF file. The original guide may be found at Linux Documentation Project. You may check other freely available programming books listed by The Free Ebook Foundation or Linux online books collected by The Online Books Page.
Getting Started
Summary
- Get the latest source code from the GitHub page.
- Install the prerequisites.
- Generate PDF and/or HTML documents.
Step 1: Get the latest source code
Make sure you can run git with an Internet connection.
$ git clone https://github.com/sysprog21/lkmpg.git && cd lkmpg
Step 2: Install the prerequisites
To generate the book from source, TeXLive (MacTeX) is required.
For Ubuntu Linux, macOS, and other Unix-like systems, run the following command(s):
# Debian / Ubuntu
$ sudo apt install make texlive-full
# Arch / Manjaro
$ sudo pacman -S make texlive-most texlive-bin
# macOS
$ brew install --cask mactex
$ sudo tlmgr update --self
Alternatively, using Docker is recommended, as it guarantees the same dependencies with our GitHub Actions workflow. After install docker engine on your machine, pull the docker image twtug/lkmpg and run in isolated containers.
# pull docker image and run it as container
$ docker pull twtug/lkmpg
$ docker run --rm -it -v $(pwd):/workdir twtug/lkmpg
nerdctl is a Docker-compatible command line tool for containerd, and you can replace the above docker commands with nerdctl counterparts.
Step 3: Generate PDF and/or HTML documents
Now we could build document with following commands:
$ make all # Generate PDF document
$ make html # Convert TeX to HTML
$ make clean # Delete generated files
License
The Linux Kernel Module Programming Guide is a free book; you may reproduce and/or modify it under the terms of the Open Software License.
Use of this work is governed by a copyleft license that can be found in the LICENSE file.
The complementary sample code is licensed under GNU GPL version 2, as same as Linux kernel.