Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754009AbbG2UyS (ORCPT ); Wed, 29 Jul 2015 16:54:18 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:45176 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752477AbbG2UyQ (ORCPT ); Wed, 29 Jul 2015 16:54:16 -0400 Date: Wed, 29 Jul 2015 13:54:07 -0700 From: josh@joshtriplett.org To: "Luis R. Rodriguez" Cc: mmarek@suse.com, jbottomley@odin.com, geert@linux-m68k.org, pebolle@tiscali.nl, herbert@gondor.apana.org.au, tiwai@suse.de, yann.morin.1998@free.fr, corbet@lwn.net, linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, roberto@dicosmo.org, zack@upsilon.cc, "Luis R. Rodriguez" Subject: Re: [PATCH] kbuild: document recursive dependency limitation / resolution Message-ID: <20150729205407.GC15480@cloud> References: <1438200556-13842-1-git-send-email-mcgrof@do-not-panic.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438200556-13842-1-git-send-email-mcgrof@do-not-panic.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4416 Lines: 96 On Wed, Jul 29, 2015 at 01:09:16PM -0700, Luis R. Rodriguez wrote: > From: "Luis R. Rodriguez" > > Recursive dependency issues with kconfig are unavoidable due to > some limitations with kconfig, since these issues are recurring > provide a hint to the user how they can resolve these dependency > issues and also document why such limitation exists. > > Cc: Geert Uytterhoeven > Cc: James Bottomley > Cc: Josh Triplett > Cc: Paul Bolle > Cc: Herbert Xu > Cc: Takashi Iwai > Cc: "Yann E. MORIN" > Cc: Michal Marek > Cc: Jonathan Corbet > Cc: linux-kbuild@vger.kernel.org > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Luis R. Rodriguez As a minor nit, I would suggest saying that making Kbuild handle this might require a full SAT solver, rather than the current phrasing that suggests that a SAT solver is the right solution to this problem. Let's wait to make that conclusion until a kbuild patch shows up. Otherwise, this seems quite sensible; thanks for documenting this bit of tribal knowledge. - Josh Triplett > I've cc'd Roberto and Stefano as I think we might be able to in the > long term use some of their work on package dependency and solvers for > this problem [0] [1] [2]. This last part -- just consider it long term > focused. > > [0] https://upsilon.cc/~zack/research/publications/splc2010-fd-deps.pdf > [1] https://ocaml.org/meetings/ocaml/2014/preferences-2014-09-05-slides.pdf > [2] https://www.youtube.com/watch?v=GSOcRQvZg8w > > Documentation/kbuild/kconfig-language.txt | 22 ++++++++++++++++++++++ > scripts/kconfig/symbol.c | 2 ++ > 2 files changed, 24 insertions(+) > > diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt > index 350f733bf2c7..7e0510d1cef7 100644 > --- a/Documentation/kbuild/kconfig-language.txt > +++ b/Documentation/kbuild/kconfig-language.txt > @@ -393,3 +393,25 @@ config FOO > depends on BAR && m > > limits FOO to module (=m) or disabled (=n). > + > +Kconfig recursive dependency limitations > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +If you've hit the Kconfig error: "recursive dependency detected" you've run > +into a recursive dependency issue with Kconfig. Kconfig does not do recursive > +dependency resolution, this has a few implications for Kconfig file writers. In > +practice it means that for instance if a driver A selects a few kconfig symbols > +another driver B which selects any of these symbols cannot negate any of the > +symbols the driver A selected. Because of this current limitation developers > +who run into this type of recursive dependency issue have two diverging > +options: > + > + a) Either swap all "select FOO" to "depends on FOO" or, > + b) Change the offending "depends on FOO" to "select FOO" > + > +Kconfig's limitations can be addressed by implementing a SAT solver for it, > +but until then, Kconfig is limitted to require developers to use one of > +the above two mechanisms to address recursive dependency issues. For more > +details you can refer to this thread and discussion: > + > +http://lkml.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com > diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c > index 70c5ee189dce..4d61b7490dad 100644 > --- a/scripts/kconfig/symbol.c > +++ b/scripts/kconfig/symbol.c > @@ -1117,6 +1117,8 @@ static void sym_check_print_recursive(struct symbol *last_sym) > if (stack->sym == last_sym) > fprintf(stderr, "%s:%d:error: recursive dependency detected!\n", > prop->file->name, prop->lineno); > + fprintf(stderr, "For a resolution refer to Documentation/kbuild/kconfig-language.txt\n"); > + fprintf(stderr, "section \"Kconfig recursive dependency limitations\"\n"); > if (stack->expr) { > fprintf(stderr, "%s:%d:\tsymbol %s %s value contains %s\n", > prop->file->name, prop->lineno, > -- > 2.3.2.209.gd67f9d5.dirty > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/