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Message-ID: <87v9ly3a0w.fsf@intel.com>
Date: Fri, 17 Apr 2020 09:23:59 +0300
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Saeed Mahameed <saeedm@...lanox.com>,
Masahiro Yamada <masahiroy@...nel.org>,
linux-kbuild@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>, Jason Gunthorpe <jgg@...pe.ca>,
Nicolas Pitre <nico@...xnic.net>,
Saeed Mahameed <saeedm@...lanox.com>, narmstrong@...libre.com,
Laurent.pinchart@...asonboard.com, leon@...nel.org,
kieran.bingham+renesas@...asonboard.com, jonas@...boo.se,
airlied@...ux.ie, jernej.skrabec@...l.net,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
linux-rdma@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword
On Thu, 16 Apr 2020, Saeed Mahameed <saeedm@...lanox.com> wrote:
> Due to the changes to the semantics of imply keyword [1], which now
> doesn't force any config options to the implied configs any more.
>
> A module (FOO) that has a weak dependency on some other modules (BAR)
> is now broken if it was using imply to force dependency restrictions.
> e.g.: FOO needs BAR to be reachable, especially when FOO=y and BAR=m.
> Which might now introduce build/link errors.
>
> There are two options to solve this:
> 1. use IS_REACHABLE(BAR), everywhere BAR is referenced inside FOO.
> 2. in FOO's Kconfig add: depends on (BAR || !BAR)
>
> The first option is not desirable, and will leave the user confused when
> setting FOO=y and BAR=m, FOO will never reach BAR even though both are
> compiled.
>
> The 2nd one is the preferred approach, and will guarantee BAR is always
> reachable by FOO if both are compiled. But, (BAR || !BAR) is really
> confusing for those who don't really get how kconfig tristate arithmetics
> work.
>
> To solve this and hide this weird expression and to avoid repetition
> across the tree, we introduce new keyword "uses" to the Kconfig options
> family.
>
> uses BAR:
> Equivalent to: depends on symbol || !symbol
> Semantically it means, if FOO is enabled (y/m) and has the option:
> uses BAR, make sure it can reach/use BAR when possible.
>
> For example: if FOO=y and BAR=m, FOO will be forced to m.
Thanks for doing this. I think *something* needs to be done to help
people grasp the "depends on FOO || FOO=n" construct; I've seen many
experienced stumble on this, it's not a rookie mistake.
I suggested "uses" as a keyword, but I'm not hung up on it.
Grepping some Kconfigs a problem I realized with *any* new keyword is
that (FOO || FOO=n) or (FOO || !FOO) is a construct that can be part of
a larger depends on.
For example,
drivers/net/ethernet/broadcom/Kconfig: depends on PCI && (IPV6 || IPV6=n)
Which means that would have to split up to two. Not ideal, but doable. I
did not find any (FOO || FOO=n) || BAR which would not work with a new
keyword.
An alternative approach that I thought of is adding a lower level
expression to tackle this? "FOO=optional" would expand to (FOO || FOO=n)
anywhere. I have no clue how hard this would be to implement.
For example:
depends on FOO=optional
=>
depends on (FOO || FOO=n)
and:
depends on FOO=optional || BAR
=>
depends on (FOO || FOO=n) || BAR
The "optional" keyword is of course open for bikeshedding, but the key
part here I think is that the "depends on" remains, and should be
obvious. And also the =optional ties better to the actual symbol being
depended on.
Thoughts?
BR,
Jani.
>
> [1] https://lore.kernel.org/linux-doc/20200302062340.21453-1-masahiroy@kernel.org/
>
> Link: https://lkml.org/lkml/2020/4/8/839
> Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: linux-kbuild@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
> Documentation/kbuild/kconfig-language.rst | 10 ++++++++++
> scripts/kconfig/expr.h | 1 +
> scripts/kconfig/lexer.l | 1 +
> scripts/kconfig/menu.c | 4 +++-
> scripts/kconfig/parser.y | 15 +++++++++++++++
> scripts/kconfig/symbol.c | 2 ++
> 6 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index a1601ec3317b..8db8c2d80794 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -130,6 +130,16 @@ applicable everywhere (see syntax).
> bool "foo"
> default y
>
> +- uses dependencies: "uses" <symbol>
> +
> + Equivalent to: depends on symbol || !symbol
> + Semantically it means, if FOO is enabled (y/m) and has the option:
> + uses BAR, make sure it can reach/use BAR when possible.
> + For example: if FOO=y and BAR=m, FOO will be forced to m.
> +
> + Note:
> + To understand how (symbol || !symbol) is actually computed, please see `Menu dependencies`_
> +
> - reverse dependencies: "select" <symbol> ["if" <expr>]
>
> While normal dependencies reduce the upper limit of a symbol (see
> diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
> index 5c3443692f34..face672fb4b4 100644
> --- a/scripts/kconfig/expr.h
> +++ b/scripts/kconfig/expr.h
> @@ -185,6 +185,7 @@ enum prop_type {
> P_CHOICE, /* choice value */
> P_SELECT, /* select BAR */
> P_IMPLY, /* imply BAR */
> + P_USES, /* uses BAR */
> P_RANGE, /* range 7..100 (for a symbol) */
> P_SYMBOL, /* where a symbol is defined */
> };
> diff --git a/scripts/kconfig/lexer.l b/scripts/kconfig/lexer.l
> index 6354c905b006..c6a0017b10d4 100644
> --- a/scripts/kconfig/lexer.l
> +++ b/scripts/kconfig/lexer.l
> @@ -102,6 +102,7 @@ n [A-Za-z0-9_-]
> "default" return T_DEFAULT;
> "defconfig_list" return T_DEFCONFIG_LIST;
> "depends" return T_DEPENDS;
> +"uses" return T_USES;
> "endchoice" return T_ENDCHOICE;
> "endif" return T_ENDIF;
> "endmenu" return T_ENDMENU;
> diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
> index e436ba44c9c5..e26161b31a11 100644
> --- a/scripts/kconfig/menu.c
> +++ b/scripts/kconfig/menu.c
> @@ -274,7 +274,9 @@ static void sym_check_prop(struct symbol *sym)
> break;
> case P_SELECT:
> case P_IMPLY:
> - use = prop->type == P_SELECT ? "select" : "imply";
> + case P_USES:
> + use = prop->type == P_SELECT ? "select" :
> + prop->type == P_IMPLY ? "imply" : "uses";
> sym2 = prop_get_symbol(prop);
> if (sym->type != S_BOOLEAN && sym->type != S_TRISTATE)
> prop_warn(prop,
> diff --git a/scripts/kconfig/parser.y b/scripts/kconfig/parser.y
> index 708b6c4b13ca..c5e9abb49d29 100644
> --- a/scripts/kconfig/parser.y
> +++ b/scripts/kconfig/parser.y
> @@ -57,6 +57,7 @@ static struct menu *current_menu, *current_entry;
> %token T_DEF_BOOL
> %token T_DEF_TRISTATE
> %token T_DEPENDS
> +%token T_USES
> %token T_ENDCHOICE
> %token T_ENDIF
> %token T_ENDMENU
> @@ -169,6 +170,7 @@ config_option_list:
> /* empty */
> | config_option_list config_option
> | config_option_list depends
> + | config_option_list uses
> | config_option_list help
> ;
>
> @@ -261,6 +263,7 @@ choice_option_list:
> /* empty */
> | choice_option_list choice_option
> | choice_option_list depends
> + | choice_option_list uses
> | choice_option_list help
> ;
>
> @@ -360,6 +363,7 @@ menu_option_list:
> /* empty */
> | menu_option_list visible
> | menu_option_list depends
> + | menu_option_list uses
> ;
>
> source_stmt: T_SOURCE T_WORD_QUOTE T_EOL
> @@ -384,6 +388,7 @@ comment_stmt: comment comment_option_list
> comment_option_list:
> /* empty */
> | comment_option_list depends
> + | comment_option_list uses
> ;
>
> /* help option */
> @@ -418,6 +423,16 @@ depends: T_DEPENDS T_ON expr T_EOL
> printd(DEBUG_PARSE, "%s:%d:depends on\n", zconf_curname(), zconf_lineno());
> };
>
> +/* uses symbol: depends on symbol || !symbol */
> +uses: T_USES symbol T_EOL
> +{
> + struct expr *symexpr = expr_alloc_symbol($2);
> +
> + menu_add_dep(expr_alloc_two(E_OR, symexpr, expr_alloc_one(E_NOT, symexpr)));
> + printd(DEBUG_PARSE, "%s:%d: uses: depends on %s || ! %s\n",
> + zconf_curname(), zconf_lineno(), $2->name, $2->name);
> +};
> +
> /* visibility option */
> visible: T_VISIBLE if_expr T_EOL
> {
> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
> index 3dc81397d003..422f7ea47722 100644
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -1295,6 +1295,8 @@ const char *prop_get_type_name(enum prop_type type)
> return "choice";
> case P_SELECT:
> return "select";
> + case P_USES:
> + return "uses";
> case P_IMPLY:
> return "imply";
> case P_RANGE:
--
Jani Nikula, Intel Open Source Graphics Center
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