.. contents:: Table of contents
   :backlinks: none

Overview
--------

*This is version 2 of Kconfiglib, which is not backwards-compatible with
Kconfiglib 1. For a summary of changes between Kconfiglib 1 and Kconfiglib 2,
see* |changes|_.

.. _changes: https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib-2-changes.txt
.. |changes| replace:: *kconfiglib-2-changes.txt*

Kconfiglib is a Python 2/3 library for scripting and extracting information
from `Kconfig
<https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt>`_
configuration systems. It can do the following, among other things:

- **Programmatically get and set symbol values**

  `allnoconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allnoconfig.py>`_ and `allyesconfig.py
  <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allyesconfig.py>`_ examples are provided, automatically verified to
  produce identical output to the standard ``make allnoconfig`` and ``make
  allyesconfig``.

- **Read and write .config files**

  The generated ``.config`` files are character-for-character identical to what
  the C implementation would generate (except for the header comment). The test
  suite relies on this, as it compares the generated files.
  
- **Write C headers**

  The generated headers use the same format as ``include/generated/autoconf.h``
  from the Linux kernel.

- **Inspect symbols**

  Printing a symbol gives output which could be fed back into a Kconfig parser
  to redefine it***. The printing function (``__str__()``) is implemented with
  public APIs, meaning you can fetch just whatever information you need as
  well.

  A helpful ``__repr__()`` is implemented on all objects too, also implemented
  with public APIs.

  \***Choice symbols get their parent choice as a dependency, which shows up as
  e.g. ``prompt "choice symbol" if <choice>`` when printing the symbol. This
  could easily be worked around if 100% reparsable output is needed.

- **Inspect expressions**

  Expressions use a simple tuple-based format that can be processed manually
  if needed. Expression printing and evaluation functions are provided,
  implemented with public APIs.

- **Inspect the menu tree**

  The underlying menu tree is exposed, including submenus created implicitly
  from symbols depending on preceding symbols. This can be used e.g. to
  implement menuconfig-like functionality.
  
  See the `menuconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/menuconfig.py>`_ example.


Here are some other features:

- **Single-file implementation**
  
  The entire library is contained in `kconfiglib.py <https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib.py>`_.

- **Runs unmodified under both Python 2 and Python 3**
  
  The code mostly uses basic Python features and has no third-party
  dependencies. The most advanced things used are probably ``@property`` and
  ``__slots__``.

- **Robust and highly compatible with the standard Kconfig C tools**
  
  The `test suite <https://github.com/ulfalizer/Kconfiglib/blob/master/testsuite.py>`_
  automatically compares output from Kconfiglib and the C tools
  by diffing the generated ``.config`` files for the real kernel Kconfig and
  defconfig files, for all ARCHes.
  
  This currently involves comparing the output for 36 ARCHes and 498 defconfig
  files (or over 18000 ARCH/defconfig combinations in "obsessive" test suite
  mode). All tests are expected to pass.

  A comprehensive suite of selftests is included as well.

- **Not horribly slow despite being a pure Python implementation**
  
  The `allyesconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allyesconfig.py>`_ example currently runs in
  about 1.3 seconds on a Core i7 2600K (with a warm file cache), including the
  ``make`` overhead from ``make scriptconfig``.
  
  Kconfiglib is especially speedy in cases where multiple ``.config`` files
  need to be processed, because the ``Kconfig`` files will only need to be parsed
  once.

  For long-running jobs, `PyPy <https://pypy.org/>`_ gives a big performance
  boost. CPython is faster for short-running jobs as PyPy needs some time to
  warm up.
  
  Kconfiglib also works well with the
  `multiprocessing <https://docs.python.org/3/library/multiprocessing.html>`_
  module. No global state is kept.

- **Warning parity with the C implementation**

  Generates the same warnings as the C implementation, plus a few extra ones.

  This is less important if the input is assumed to be well-formed, but makes
  Kconfiglib a viable replacement for the C tools if e.g. a ``menuconfig``
  interface is added.

  All warnings point out the location(s) in the ``Kconfig`` files where a
  symbol is defined, where applicable.

- **Windows support**

  Nothing Linux-specific is used. Universal newlines mode is used for both
  Python 2 and Python 3.
  
  The `Zephyr <https://www.zephyrproject.org/>`_ project uses Kconfiglib to
  generate ``.config`` files and C headers on Linux as well as Windows.

- **Internals that (mostly) mirror the C implementation**
  
  While being simpler to understand and tweak.
  
Documentation
-------------

Kconfiglib comes with extensive documentation in the form of docstrings. To view it, run e.g.
the following command:

.. code:: sh

    $ pydoc kconfiglib
    
For HTML output, add ``-w``:

.. code:: sh

    $ pydoc -w kconfiglib
    
A good starting point is to read the module docstring (which you could also just read directly
at the beginning of `kconfiglib.py <https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib.py>`_). It gives an introduction to symbol
values, the menu tree, and expressions.

After reading the module docstring, a good next step is to read the ``Kconfig`` class
documentation, and then the documentation for the ``Symbol``, ``Choice``, and ``MenuNode``
classes.

Please tell me if something is unclear to you or can be explained better.

Installation
------------

Installation with pip
~~~~~~~~~~~~~~~~~~~~~

Kconfiglib is available on `PyPI <https://pypi.python.org/pypi/kconfiglib/>`_ and can be
installed with e.g.

.. code::

    $ pip(3) install kconfiglib --user

All releases have a corresponding tag in the git repository, e.g. ``v3.0.0``
(the latest version).

`Semantic versioning <http://semver.org/>`_ is used. There's been a
`tiny change <https://github.com/ulfalizer/Kconfiglib/commit/e8b4ecb6ff6ccc1c7be0818314fbccda2ef2b2ee>`_
to the behavior of the API (which I don't think will affect anyone), which is
why the major version is at 3 rather than 2.

Installation for the Linux kernel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See the module docstring at the top of `kconfiglib.py <https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib.py>`_.

Manual installation
~~~~~~~~~~~~~~~~~~~

The entire library is contained in
`kconfiglib.py <https://github.com/ulfalizer/Kconfiglib/blob/master/kconfiglib.py>`_.
Just drop it somewhere.

Examples
--------

Example scripts
~~~~~~~~~~~~~~~

The `examples/ <https://github.com/ulfalizer/Kconfiglib/blob/master/examples>`_ directory contains some simple example scripts. Among these are the following ones. Make sure you run them with the latest version of Kconfiglib, as they might make use of newly added features.

- `allnoconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allnoconfig.py>`_, `allnoconfig_simpler.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allnoconfig_simpler.py>`_, and `allyesconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/allyesconfig.py>`_ implement ``make allnoconfig`` and ``make allyesconfig`` in various ways. Demonstrates menu tree walking and value setting.

- `defconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/defconfig.py>`_ has the same effect as going into ``make menuconfig`` and immediately saving and exiting.

- `eval_expr.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/eval_expr.py>`_ evaluates an expression in the context of a configuration.

- `find_symbol.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/find_symbol.py>`_ searches through expressions to find references to a symbol, also printing a "backtrace" with parents for each reference found.

- `help_grep.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/help_grep.py>`_ searches for a string in all help texts.

- `print_tree.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/print_tree.py>`_ prints a tree of all configuration items.

- `list_undefined.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/list_undefined.py>`_ finds references to symbols that are not defined by any architecture in the Linux kernel.

- `merge_config.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/merge_config.py>`_ merges configuration fragments to produce a complete .config, similarly to ``scripts/kconfig/merge_config.sh`` from the kernel.

- `oldconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/oldconfig.py>`_ provides ``make oldconfig`` functionality, prompting the user for the values of new symbols to update an old ``.config`` file.

- `menuconfig.py <https://github.com/ulfalizer/Kconfiglib/blob/master/examples/menuconfig.py>`_ implements a configuration interface that uses notation similar to ``make menuconfig``. It's deliberately kept as simple as possible to demonstrate just the core concepts, and isn't something you'd actually want to use. Here's a screenshot:

.. code-block::

    ======== Example Kconfig configuration ========

    [*] Enable loadable module support (MODULES)
        Bool and tristate symbols
            [*] Bool symbol (BOOL)
                    [ ] Dependent bool symbol (BOOL_DEP)
                    < > Dependent tristate symbol (TRI_DEP)
                    [ ] First prompt (TWO_MENU_NODES)
            < > Tristate symbol (TRI)
            [ ] Second prompt (TWO_MENU_NODES)
                *** These are selected by TRI_DEP ***
            < > Tristate selected by TRI_DEP (SELECTED_BY_TRI_DEP)
            < > Tristate implied by TRI_DEP (IMPLIED_BY_TRI_DEP)
        String, int, and hex symbols
            (foo) String symbol (STRING)
            (747) Int symbol (INT)
            (0xABC) Hex symbol (HEX)
        Various choices
            -*- Bool choice (BOOL_CHOICE)
                    --> Bool choice sym 1 (BOOL_CHOICE_SYM_1)
                        Bool choice sym 2 (BOOL_CHOICE_SYM_2)
            {M} Tristate choice (TRI_CHOICE)
                    < > Tristate choice sym 1 (TRI_CHOICE_SYM_1)
                    < > Tristate choice sym 2 (TRI_CHOICE_SYM_2)
            [ ] Optional bool choice (OPT_BOOL_CHOICE)

    Enter a symbol/choice name, "load_config", or "write_config" (or press CTRL+D to exit): BOOL
    Value for BOOL (available: n, y): n
    ...
    
I'm not currently interested in implementing a (more usable) menuconfig myself, but all the infrastructure
for a great one should be there if you want to give it a go. I'll help you out with any questions you might
have.

Real-world examples
~~~~~~~~~~~~~~~~~~~

These use the older Kconfiglib 1 API, which was clunkier and not as general (functions instead of properties, no direct access to the menu structure or properties, uglier ``__str__()`` output):

- `genboardscfg.py <http://git.denx.de/?p=u-boot.git;a=blob;f=tools/genboardscfg.py;hb=HEAD>`_ from `Das U-Boot <http://www.denx.de/wiki/U-Boot>`_ generates some sort of legacy board database by pulling information from a newly added Kconfig-based configuration system (as far as I understand it :).

- `gen-manual-lists.py <https://git.busybox.net/buildroot/tree/support/scripts/gen-manual-lists.py?id=5676a2deea896f38123b99781da0a612865adeb0>`_ generated listings for an appendix in the `Buildroot <https://buildroot.org>`_ manual. (The listing has since been removed.)

- `gen_kconfig_doc.py <https://github.com/espressif/esp-idf/blob/master/docs/gen-kconfig-doc.py>`_ from the `esp-idf <https://github.com/espressif/esp-idf>`_ project generates documentation from Kconfig files.

- `SConf <https://github.com/CoryXie/SConf>`_ builds an interactive configuration interface (like ``menuconfig``) on top of Kconfiglib, for use e.g. with `SCons <scons.org>`_.

- `kconfig-diff.py <https://gist.github.com/dubiousjim/5638961>`_ -- a script by `dubiousjim <https://github.com/dubiousjim>`_ that compares kernel configurations.

- Originally, Kconfiglib was used in chapter 4 of my `master's thesis <http://liu.diva-portal.org/smash/get/diva2:473038/FULLTEXT01.pdf>`_ to automatically generate a "minimal" kernel for a given system. Parts of it bother me a bit now, but that's how it goes with old work.

Sample ``make iscriptconfig`` session
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following log should give some idea of the functionality available in the API:

.. code-block::

    $ make iscriptconfig
    A Kconfig instance 'kconf' for the architecture x86 has been created.
    >>> kconf  # Calls Kconfig.__repr__()
    <configuration with 13711 symbols, main menu prompt "Linux/x86 4.14.0-rc7 Kernel Configuration", srctree ".", config symbol prefix "CONFIG_", warnings enabled, undef. symbol assignment warnings disabled>
    >>> kconf.mainmenu_text  # Expanded main menu text
    'Linux/x86 4.14.0-rc7 Kernel Configuration'
    >>> kconf.top_node  # The implicit top-level menu
    <menu node for menu, prompt "Linux/$ARCH $KERNELVERSION Kernel Configuration" (visibility y), deps y, 'visible if' deps y, has child, Kconfig:5>
    >>> kconf.top_node.list  # First child menu node
    <menu node for symbol SRCARCH, deps y, has next, Kconfig:7>
    >>> print(kconf.top_node.list)  # Calls MenuNode.__str__()
    config SRCARCH
    	string
    	option env="SRCARCH"
    	default "x86"
    
    >>> sym = kconf.top_node.list.next.item  # Item contained in next menu node
    >>> print(sym)  # Calls Symbol.__str__()
    config 64BIT
    	bool
    	prompt "64-bit kernel" if ARCH = "x86"
    	default ARCH != "i386"
    	help
    	  Say yes to build a 64-bit kernel - formerly known as x86_64
    	  Say no to build a 32-bit kernel - formerly known as i386
    
    >>> sym  # Calls Symbol.__repr__()
    <symbol 64BIT, bool, "64-bit kernel", value y, visibility y, direct deps y, arch/x86/Kconfig:2>
    >>> sym.assignable  # Currently assignable values (0, 1, 2 = n, m, y)
    (0, 2)
    >>> sym.set_value(0)  # Set it to n
    True
    >>> sym.tri_value  # Check the new value
    0
    >>> sym = kconf.syms["X86_MPPARSE"]  # Look up symbol by name
    >>> print(sym)
    config X86_MPPARSE
    	bool
    	prompt "Enable MPS table" if (ACPI || SFI) && X86_LOCAL_APIC
    	default "y" if X86_LOCAL_APIC
    	help
    	  For old smp systems that do not have proper acpi support. Newer systems
    	  (esp with 64bit cpus) with acpi support, MADT and DSDT will override it
    
    >>> default = sym.defaults[0]  # Fetch its first default
    >>> sym = default[1]  # Fetch the default's condition (just a Symbol here)
    >>> print(sym)  # Print it. Dependencies are propagated to properties, like in the C implementation.
    config X86_LOCAL_APIC
    	bool
    	default "y" if X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
    	select IRQ_DOMAIN_HIERARCHY if X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
    	select PCI_MSI_IRQ_DOMAIN if PCI_MSI && (X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI)
    
    >>> sym.nodes  # Show the MenuNode(s) associated with it
    [<menu node for symbol X86_LOCAL_APIC, deps n, has next, arch/x86/Kconfig:1015>]
    >>> kconfiglib.expr_str(sym.defaults[0][1])  # Print the default's condition
    'X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI'
    >>> kconfiglib.expr_value(sym.defaults[0][1])  # Evaluate it (0 = n)
    0
    >>> kconf.syms["64BIT"].set_value(2)
    True
    >>> kconfiglib.expr_value(sym.defaults[0][1])  # Evaluate it again (2 = y)
    2
    >>> kconf.write_config("myconfig")  # Save a .config
    >>> ^D
    $ cat myconfig
    # Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)
    CONFIG_64BIT=y
    CONFIG_X86_64=y
    CONFIG_X86=y
    CONFIG_INSTRUCTION_DECODER=y
    CONFIG_OUTPUT_FORMAT="elf64-x86-64"
    CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"
    CONFIG_LOCKDEP_SUPPORT=y
    CONFIG_STACKTRACE_SUPPORT=y
    CONFIG_MMU=y
    ...
 
Test suite
----------

The test suite is run with

.. code::

    $ python(3) Kconfiglib/testsuite.py
    
`pypy <https://pypy.org/>`_ works too, and is much speedier for everything except ``allnoconfig.py``/``allnoconfig_simpler.py``/``allyesconfig.py``, where it doesn't have time to warm up since
the scripts are run via ``make scriptconfig``.

The test suite must be run from the top-level kernel directory. It requires that the
Kconfiglib git repository has been cloned into it and that the makefile patch has been applied.

To get rid of warnings generated for the kernel ``Kconfig`` files, add ``2>/dev/null`` to the command to
discard ``stderr``.

**NOTE: Forgetting to apply the Makefile patch will cause some tests that compare generated configurations to fail**

**NOTE: The test suite overwrites .config in the kernel root, so make sure to back it up.**

The test suite consists of a set of selftests and a set of compatibility tests that
compare configurations generated by Kconfiglib with
configurations generated by the C tools, for a number of cases. See
`testsuite.py <https://github.com/ulfalizer/Kconfiglib/blob/master/testsuite.py>`_
for the available options. You might want to use the "speedy" option to speed things
up a bit.

The `tests/reltest <https://github.com/ulfalizer/Kconfiglib/blob/master/tests/reltest>`_ script runs the test suite
and all the example scripts for both Python 2 and Python 3, verifying that everything works.

The test suite might fail for a few configurations for kernels older than April 2016,
when a fix was added to Kconfig that's also mirrored in Kconfiglib
(see `this commit <https://github.com/ulfalizer/Kconfiglib/commit/35ea8d5f1d63bdc9f8642f5ce4445e8f7c914385>`_).
This is harmless, and only counts as a fail since the test suite compares literal
output from the kconfig version that's bundled with the kernel.

A lot of time is spent waiting around for ``make`` and the C utilities (which need to reparse all the
Kconfig files for each defconfig test). Adding some multiprocessing to the test suite would make sense
too.

Notes
-----

* I sometimes see people add custom output formats, which is pretty straightforward to do (see the implementations of 
  ``write_autoconf()`` and ``write_config()`` for a template). If you come up with something you think might
  be useful to other people, I'm happy to take it in upstream. Batteries included and all that.

* Kconfiglib assumes the modules symbol is ``MODULES``, which is backwards-compatible.
  A warning is printed by default if ``option modules`` is set on some other symbol.
  
  Let me know if you need proper ``option modules`` support. It wouldn't be that
  hard to add.

* `fpemud <https://github.com/fpemud>`_ has put together
  `Python bindings <https://github.com/fpemud/pylkc>`_ to internal functions in the C
  implementation. This is an alternative to Kconfiglib's all-Python approach.

* The test suite failures (should be the only ones) for the following Blackfin
  defconfigs on e.g. Linux 3.7.0-rc8 are due to
  `a bug in the C implementation <https://lkml.org/lkml/2012/12/5/458>`_:

  * ``arch/blackfin/configs/CM-BF537U_defconfig``
  * ``arch/blackfin/configs/BF548-EZKIT_defconfig``
  * ``arch/blackfin/configs/BF527-EZKIT_defconfig``
  * ``arch/blackfin/configs/BF527-EZKIT-V2_defconfig``
  * ``arch/blackfin/configs/TCM-BF537_defconfig``

Thanks
------

Thanks to `Philip Craig <https://github.com/philipc>`_ for adding
support for the ``allnoconfig_y`` option and fixing an obscure issue
with ``comment``\s inside ``choice``\s (that didn't affect correctness but
made outputs differ). ``allnoconfig_y`` is used to force certain symbols
to ``y`` during ``make allnoconfig`` to improve coverage.

License
-------

See `LICENSE.txt <https://github.com/ulfalizer/Kconfiglib/blob/master/LICENSE.txt>`_. SPDX license identifiers are used in the
source code.