On Wed, Jul 29, 2015 at 01:09:16PM -0700, Luis R. Rodriguez wrote: > From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx> > > 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 <geert@xxxxxxxxxxxxxx> > Cc: James Bottomley <jbottomley@xxxxxxxx> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > Cc: Paul Bolle <pebolle@xxxxxxxxxx> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Cc: Takashi Iwai <tiwai@xxxxxxx> > Cc: "Yann E. MORIN" <yann.morin.1998@xxxxxxx> > Cc: Michal Marek <mmarek@xxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: linux-kbuild@xxxxxxxxxxxxxxx > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx> 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@xxxxxxxxxxxxxxxx > 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-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
