linux-kernel - Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword

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Date:   Mon, 20 Apr 2020 10:53:13 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nicolas Pitre <nico@...xnic.net>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Leon Romanovsky <leon@...nel.org>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        jonas@...boo.se, David Airlie <airlied@...ux.ie>,
        jernej.skrabec@...l.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, linux-rdma@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword

On Sun, Apr 19, 2020 at 04:00:43AM +0900, Masahiro Yamada wrote:

> People would wonder, "what 'uses FOO' means?",
> then they would find the explanation in kconfig-language.rst:
> 
>   "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."
> 
> To understand this correctly, people must study
> the arithmetic of (symbol || !symbol) anyway.

I think people will just cargo-cult copy it and not think too hard
about how kconfig works.

The descriptions in kconfig-language.rst can be improved to better
guide C people using kconfig without entirely understanding
it. Something like:

 BAR depends on FOO // BAR selects FOO: BAR requires functionality from
 FOO

 BAR uses FOO: BAR optionally consumes functionality from FOO using
 IS_ENABLED

 BAR implies FOO: BAR optionally consumes functionality from FOO using
 IS_REACHABLE

Now someone adding IS_ENABLED or IS_REACHABLE checks to C code knows
exactly what to put in the kconfig.

Jason