/usr/src/linux/Documentation/

The /usr/src/linux/Documentation/ directory contains a wealth of information about various aspects of the Linux kernel. This directory is an invaluable resource for developers, system administrators, and anyone interested in understanding the kernel's features, subsystems, and development practices. Here's an overview of what you can find in the Documentation directory and how to navigate and utilize it effectively.

Structure of the Documentation Directory

The Documentation directory typically includes a mix of plain text files, subdirectories, and sometimes markdown or reStructuredText (reST) files. These documents cover a broad range of topics.

Common Subdirectories and Files

1. admin-guide/:

   • Purpose: Contains guides for system administrators on configuring and managing the kernel.

   • Examples:

     • kernel-parameters.txt: Detailed explanations of kernel boot parameters.

     • sysctl/: Documentation on sysctl interfaces for runtime kernel parameter tuning.

2. arm/:

   • Purpose: ARM architecture-specific documentation.

   • Examples: Information on ARM-specific kernel features, supported platforms, and configuration options.

3. block/:

   • Purpose: Documentation on block layer subsystems and block device drivers.

   • Examples: Guides on developing and configuring block device drivers.

4. filesystems/:

   • Purpose: Details on various filesystem implementations supported by the Linux kernel.

   • Examples: Documentation on ext4, XFS, Btrfs, and other filesystems.

5. networking/:

   • Purpose: Guides and references for networking subsystems and protocols.

   • Examples: Details on TCP/IP stack, network drivers, and network configuration.

6. input/:

   • Purpose: Documentation related to input devices and subsystems.

   • Examples: Information on keyboard, mouse, touchscreen drivers, and configuration.

7. dev-tools/:

   • Purpose: Tools and scripts for kernel development and debugging.

   • Examples: Guides on using perf, ftrace, and other kernel development tools.

8. core-api/:

   • Purpose: Core kernel APIs and programming interfaces.

   • Examples: Details on locking mechanisms, memory management APIs, and kernel data structures.

9. driver-api/:

   • Purpose: Documentation for writing and maintaining kernel drivers.

   • Examples: Guides on driver model, device registration, and power management.

10. kernel-parameters.txt:

    • Purpose: Detailed list of kernel boot parameters and their descriptions.

    • Usage: Reference for configuring kernel behavior at boot time.

11. process/Changes:

    • Purpose: Information on changes between kernel versions.

    • Usage: Helps developers understand what has changed or been deprecated.

12. process/SubmittingPatches:

    • Purpose: Guidelines for submitting patches to the kernel.

    • Usage: Ensures that contributions follow the kernel's development process.

Using the Documentation

1. Navigating the Documentation:

   • Text Files: Use a text editor (e.g., vim, nano, less) to view plain text files.

   • reStructuredText/Markdown: Use appropriate tools or renderers (e.g., rst2html, markdown) to view formatted documents.

2. Searching for Information:

   • Grep: Use grep to search for keywords within the documentation files.

     grep -r "keyword" /usr/src/linux/Documentation/

3. Referencing Specific Topics:

   • Example: To learn about kernel boot parameters, open the kernel-parameters.txt file.

     less /usr/src/linux/Documentation/admin-guide/kernel-parameters.txt

4. Staying Updated:

   • Regularly check the Changes document to stay informed about updates and modifications in new kernel versions.

Example Topics and Usage

1. Kernel Parameters:

   • File: admin-guide/kernel-parameters.txt

   • Example: To find information on a specific boot parameter like panic=, search within the file.

     less /usr/src/linux/Documentation/admin-guide/kernel-parameters.txt
     /panic=

2. Filesystem Documentation:

   • Directory: filesystems/

   • Example: To learn about ext4 filesystem features and configuration.

     less /usr/src/linux/Documentation/filesystems/ext4.txt

3. Submitting Patches:

   • File: process/SubmittingPatches

   • Usage: Follow guidelines to contribute to the kernel development.

     less /usr/src/linux/Documentation/process/SubmittingPatches

Conclusion

The /usr/src/linux/Documentation/ directory is an essential resource for anyone working with the Linux kernel. It provides comprehensive information on various kernel subsystems, configuration options, development practices, and much more. Familiarity with this directory and its contents can significantly enhance your understanding and capability to work with the Linux kernel.