Kconfig User Guide

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I. Overview

Kconfig provides a mechanism for project configuration at compile time, supporting various types of configuration options, such as integers, strings, and booleans. Through the Kconfig files, developers can define the dependencies between options, configure default values, and define their combination rules.For detailed information about the Kconfig language, refer to the Kconfig documentation.

Similar to most large operating systems, openvela utilizes Kconfig to manage project configurations. Developers can perform configuration tasks through the visual interface provided by menuconfig, enabling the efficient building and tailoring of the openvela system.

II. Usage Examples

To modify configuration parameters during project setup, perform the following verification and configuration procedure:

1. Review the configuration item status.

   You can examine the .config file to determine whether the configuration has been set and if its value meets the expected criteria. If it does, you may use it as is; otherwise, it is recommended to adjust the setting using the menuconfig tool.

   Note: Using the menuconfig tool ensures that all configuration dependencies are complete and correct.

2. Example: Configuring the KVDB storage path.

   Take the database storage path configuration for KVDB, CONFIG_KVDB_PERSIST_PATH, as an example:

   • By default, configuration options use their default values and will not appear in the defconfig file.

   • "In the .config file you can observe that its default value is set to "/data/persist.db". If a different value is desired, you may locate and adjust the corresponding configuration option through menuconfig."

     

3. Example: Enable the FTL_WRITEBUFFER configuration. If you need to enable the FTL_WRITEBUFFER configuration, follow these steps:

   1. Verify the configuration's presence in .config. If absent, enable via menuconfig instead of forcibly adding CONFIG_FTL_WRITEBUFFER=y to defconfig

      

   2. CONFIG_FTL_WRITEBUFFER depends on CONFIG_DRVR_WRITEBUFFER. If CONFIG_DRVR_WRITEBUFFER is not enabled simultaneously, manually modifying the defconfig file will not take effect.

   3. The menuconfig interface automatically resolves dependency chains and persists validated changes to defconfig:

      CONFIG_FTL_WRITEBUFFER=y  
      CONFIG_DRVR_WRITEBUFFER=y  
      

III. Purpose of Each File

During the initial build, openvela locates the corresponding project's defconfig by using the specified arch and board parameters, which serves as the system's initial configuration. Based on this file, openvela expands and combines configurations to ultimately generate a complete .config file. The generated .config file is then copied to config.h to facilitate conditional compilation in the code and support runtime usage.

1. Detailed Description of Each File

1. defconfig

   • The minimal set of system configurations defines the default basic configuration options. The system generates the complete .config configuration file based on this file and the dependencies among configuration options.
   • All configuration options in the defconfig file are arranged in alphabetical order. It is recommended to add or remove configuration options using the menuconfig tool. Direct modifications to the defconfig file may result in redundant configurations or ordering inconsistencies.

2. .config

   • The .config file is the complete configuration generated from the defconfig file, incorporating all extended and combined configuration options.
   • The menuconfig interface reads the local .config file for user-customized configuration adjustments and automatically propagates validated changes back to the defconfig file upon completion.

3. config.h

   • The config.h file is generated from the .config file, containing all configuration information to support conditional compilation and runtime operations in the code.

2. Build Process Example

The following diagram illustrates a typical build configuration workflow:

Execute build commands:

./build.sh vendor/sim/boards/vela/config/vela menuconfig
./build.sh vendor/sim/boards/vela/config/vela -j8

3. File Path Examples

Based on the openvela simulator environment, the typical file paths are as follows:

• defconfig file path：vendor/sim/boards/vela/configs/vela/defconfig
• .config file path：nuttx/.config
• config.h file path：nuttx/include/config.h

IV. Usage Instructions

The following diagram illustrates a typical build configuration workflow:

1. Disable a feature in Kconfig configuration.

   Before disabling a Kconfig configuration option, make sure it is not selected by any other configuration options via the select keyword. If there are dependencies, those dependencies must be resolved first.

2. Open the visual configuration interface.

   Use the menuconfig command to open the visual configuration interface, for example:

   ./build.sh vendor/sim/boards/openvela/configs/openvela menuconfig  
   

   

3. Use the menuconfig command to open the visual configuration interface, for example:

   In the menuconfig interface, you can enter / followed by a configuration keyword to search. For example, to search for EXAMPLES_HELLO:

   Note: If the search results contain depends on dependencies, type ? to continue searching for dependent configurations and enable them.

   

4. Select and navigate configuration options.

   Use the arrow keys to navigate up and down, and press Enter to select the corresponding option.

   

5. View configuration details.

   After selecting a configuration item, press Shift + ? to display its detailed documentation and file location information.

   

6. Select specific options

   Follow configuration prompts, such as the option number in brackets (e.g., '1'), to navigate to sub-option interfaces.

   

7. Modify configuration values

   Within the selected configuration option, you can input values based on the configuration type.

   • int: A specific integer value must be entered.

   • bool: Toggle the state by pressing y (enable) or the space key.

   • String type: Enter the string directly as the configuration value.

8. Save changes or exit

   • Press the ESC key to exit the configuration interface and press y when prompted to save changes.
   • To force exit, use Ctrl + C, but this may result in loss of unsaved changes.

V. Related Documents

The following links provide additional details about using Kconfig:

• Kernel Documentation - Kconfig Language