[RFC,v3,00/12] kconfig: add support for conflict resolution

Message

Thorsten Berger Oct. 22, 2021, 1:34 p.m. UTC

Hi,

Configuring a kernel requires a forward enabling approach where one
enables each option one needs at a time. If one enables an option
that selects other options, these options are no longer de-selectable
by design. Likewise, if one has enabled an option which creates a
conflict with a secondary option one wishes to enable, one cannot
easily enable that secondary option, unless one is willing to spend
time analyzing the dependencies that led to this conflict. Sometimes,
these conflicts are not easy to understand [0,1].

This patch series (for linux-next) provides support to enable users to
express their desired target configuration and display possible resolutions
to their conflicts. This support is provided within xconfig.

Conflict resolution is provided by translating kconfig's configuration
option tree to a propositional formula, and then allowing our resolution
algorithm, which uses a SAT solver (picosat, implemented in C) calculate
the possible fixes for an expressed target kernel configuration.

New UI extensions are made to xconfig with panes and buttons to allow users
to express new desired target options, calculate fixes, and apply any of
found solutions.

We created a separate test infrastructure that we used to validate the
correctness of the suggestions made. It shows that our resolution
algorithm resolves around 95% of the conflicts. We plan to incorporate
this with a later patch series.

We envision that our translation of the kconfig option tree into into a
propositional formula could potentially also later be repurposed to
address other problems. An example is checking the consistency
between the use of ifdefs and logic expressed in kconfig files.
We suspect that this could, for example, help avoid invalid kconfig
configurations and help with ifdef maintenance.

You can see a YouTube video demonstrating this work [2]. This effort is
part of the kernelnewbies Kconfig-SAT project [3], the approach and effort is
also explained in detail in our paper [4]. It is also our attempt at contributing
back to the kernel community, whose configurator researchers studied a lot.

Patches applicable to linux-next.

[0] https://gsd.uwaterloo.ca/sites/default/files/vamos12-survey.pdf
[1] https://www.linux-magazine.com/Issues/2021/244/Kconfig-Deep-Dive
[2] https://youtu.be/vyX7zCRiLKU
[3] https://kernelnewbies.org/KernelProjects/kconfig-sat
[4] http://www.cse.chalmers.se/~bergert/paper/2021-icseseip-configfix.pdf

Thanks from the team! (and thanks to Luis Chamberlain for guiding us here)

Co-developed-by: Patrick Franz <[e-mail]>
Signed-off-by: Patrick Franz <[e-mail]>
Co-developed-by: Ibrahim Fayaz <[e-mail]>
Signed-off-by: Ibrahim Fayaz <[e-mail]>
Reviewed-by: Luis Chamberlain <[e-mail]>
Tested-by: Evgeny Groshev <[e-mail]>
Suggested-by: Sarah Nadi <[e-mail]>
Suggested-by: Thorsten Berger <[e-mail]>
Signed-off-by: Thorsten Berger <[e-mail]>

Patrick Franz (12):
  Add picosat.h
  Add picosat.c (1/3)
  Add picosat.c (2/3)
  Add picosat.c (3/3)
  Add definitions
  Add files for building constraints
  Add files for handling expressions
  Add files for RangeFix
  Add files with utility functions
  Add tools
  Add xconfig-modifications
  Simplify dependencies for MODULE_SIG_KEY_TYPE_RSA &
    MODULE_SIG_KEY_TYPE_ECDSA

 certs/Kconfig                    |    3 +-
 scripts/kconfig/Makefile         |   19 +-
 scripts/kconfig/cf_constraints.c | 1219 +++++
 scripts/kconfig/cf_constraints.h |   23 +
 scripts/kconfig/cf_defs.h        |  233 +
 scripts/kconfig/cf_expr.c        | 2146 ++++++++
 scripts/kconfig/cf_expr.h        |  237 +
 scripts/kconfig/cf_rangefix.c    | 1017 ++++
 scripts/kconfig/cf_rangefix.h    |   18 +
 scripts/kconfig/cf_satutils.c    |  536 ++
 scripts/kconfig/cf_satutils.h    |   30 +
 scripts/kconfig/cf_utils.c       |  510 ++
 scripts/kconfig/cf_utils.h       |   90 +
 scripts/kconfig/cfconfig.c       |  176 +
 scripts/kconfig/cfoutconfig.c    |  128 +
 scripts/kconfig/configfix.c      |  420 ++
 scripts/kconfig/configfix.h      |   41 +
 scripts/kconfig/expr.h           |   13 +
 scripts/kconfig/picosat.c        | 8502 ++++++++++++++++++++++++++++++
 scripts/kconfig/picosat.h        |  658 +++
 scripts/kconfig/qconf.cc         | 1003 +++-
 scripts/kconfig/qconf.h          |  179 +-
 22 files changed, 16943 insertions(+), 258 deletions(-)
 create mode 100644 scripts/kconfig/cf_constraints.c
 create mode 100644 scripts/kconfig/cf_constraints.h
 create mode 100644 scripts/kconfig/cf_defs.h
 create mode 100644 scripts/kconfig/cf_expr.c
 create mode 100644 scripts/kconfig/cf_expr.h
 create mode 100644 scripts/kconfig/cf_rangefix.c
 create mode 100644 scripts/kconfig/cf_rangefix.h
 create mode 100644 scripts/kconfig/cf_satutils.c
 create mode 100644 scripts/kconfig/cf_satutils.h
 create mode 100644 scripts/kconfig/cf_utils.c
 create mode 100644 scripts/kconfig/cf_utils.h
 create mode 100644 scripts/kconfig/cfconfig.c
 create mode 100644 scripts/kconfig/cfoutconfig.c
 create mode 100644 scripts/kconfig/configfix.c
 create mode 100644 scripts/kconfig/configfix.h
 create mode 100644 scripts/kconfig/picosat.c
 create mode 100644 scripts/kconfig/picosat.h