From: Saeed Mahameed <saeedm@mellanox.com>
To: "masahiroy@kernel.org" <masahiroy@kernel.org>,
"jani.nikula@linux.intel.com" <jani.nikula@linux.intel.com>,
"nico@fluxnic.net" <nico@fluxnic.net>
Cc: "Laurent.pinchart@ideasonboard.com"
<Laurent.pinchart@ideasonboard.com>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
"linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>,
"jgg@ziepe.ca" <jgg@ziepe.ca>,
"airlied@linux.ie" <airlied@linux.ie>,
"jernej.skrabec@siol.net" <jernej.skrabec@siol.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"jonas@kwiboo.se" <jonas@kwiboo.se>,
"narmstrong@baylibre.com" <narmstrong@baylibre.com>,
"kieran.bingham+renesas@ideasonboard.com"
<kieran.bingham+renesas@ideasonboard.com>,
"leon@kernel.org" <leon@kernel.org>
Subject: Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword
Date: Tue, 21 Apr 2020 04:24:10 +0000 [thread overview]
Message-ID: <45b9efec57b2e250e8e39b3b203eb8cee10cb6e8.camel@mellanox.com> (raw)
In-Reply-To: <87v9lu1ra6.fsf@intel.com>
On Mon, 2020-04-20 at 11:43 +0300, Jani Nikula wrote:
> On Sun, 19 Apr 2020, Masahiro Yamada <masahiroy@kernel.org> wrote:
> > On Sun, Apr 19, 2020 at 4:11 AM Nicolas Pitre <nico@fluxnic.net>
> > wrote:
> > > On Sun, 19 Apr 2020, Masahiro Yamada wrote:
> > >
> > > > (FOO || !FOO) is difficult to understand, but
> > > > the behavior of "uses FOO" is as difficult to grasp.
> > >
> > > Can't this be expressed as the following instead:
> > >
> > > depends on FOO if FOO
> > >
> > > That would be a little clearer.
> > >
> > >
> > > Nicolas
> >
> >
> > 'depends on' does not take the 'if <expr>'
> >
> > 'depends on A if B' is the syntax sugar of
> > 'depends on (A || !B), right ?
> >
> > I do not know how clearer it would make things.
> >
> > depends on (m || FOO != m)
> > is another equivalent, but we are always
> > talking about a matter of expression.
> >
> >
> > How important is it to stick to
> > depends on (FOO || !FOO)
> > or its equivalents?
> >
> >
> > If a driver wants to use the feature FOO
> > in most usecases, 'depends on FOO' is sensible.
> >
> > If FOO is just optional, you can get rid of the dependency,
> > and IS_REACHABLE() will do logically correct things.
>
> If by logically correct you mean the kernel builds, you're
> right. However the proliferation of IS_REACHABLE() is making the
> kernel
> config *harder* to understand. User enables FOO=m and expects BAR to
> use
> it, however if BAR=y it silently gets ignored. I have and I will
> oppose
> adding IS_REACHABLE() usage to i915 because it's just silently
> accepting
> configurations that should be flagged and forbidden at kconfig stage.
>
> > I do not think IS_REACHABLE() is too bad,
> > but if it is confusing, we can add one more
> > option to make it explicit.
> >
> >
> >
> > config DRIVER_X
> > tristate "driver x"
> >
> > config DRIVER_X_USES_FOO
> > bool "use FOO from driver X"
> > depends on DRIVER_X
> > depends on DRIVER_X <= FOO
> > help
> > DRIVER_X works without FOO, but
> > Using FOO will provide better usability.
> > Say Y if you want to make driver X use FOO.
> >
> >
> >
> > Of course,
> >
> > if (IS_ENABLED(CONFIG_DRIVER_X_USES_FOO))
> > foo_init();
> >
> > works like
> >
> > if (IS_REACHABLE(CONFIG_FOO))
> > foo_init();
> >
> >
> > At lease, it will eliminate a question like
> > "I loaded the module FOO, I swear.
> > But my built-in driver X still would not use FOO, why?"
>
and duplicate this all over just to avoid new keyword.
> Please let's not make that a more widespread problem than it already
> is. I have yet to hear *one* good rationale for allowing that in the
> first place. And if that pops up, you can make it work by using
> IS_REACHABLE() *without* the depends, simply by checking if the
> module
> is there.
>
> Most use cases increasingly solved by IS_REACHABLE() should use the
> "depends on FOO || FOO=n" construct, but the problem is that's not
> widely understood. I'd like to have another keyword for people to
> copy-paste into their Kconfigs.
>
+1
do all C developers know how the C compiler works ? of course not !
Same goes here, there is a demand for a new keyword, so people will
avoid copy and pate and can use the kconfig language in a higher
simplified level.
I just did a quick grep to find out how really people use depend on:
# All usage of depends on
$ git ls-files | grep Kconfig | xargs grep -E "depends\s+on" | wc -l
15071
# simple single symbol expression usage
$ git ls-files | grep Kconfig | xargs grep -E "depends\s+on\s+[A-Za-z0-
9_]+\s*$" | wc -l
8889
almost 60%..
people really like simple things especially for the tools they are
using "like kconfig", no one really wants to understand how it really
work under the hood if it is a one time thing that you need to setup
for your kernel project, unless it is really necessary ..
I wonder how many of those 8889 cases wanted a weak dependency but
couldn't figure out how to do it ?
Users of depends on FOO || !FOO
$ git ls-files | grep Kconfig | xargs grep -E \
"depends\s+on\s+([A-Za-z0-9_]+)\s*\|\|\s*(\!\s*\1|\1\s*=\s*n)" \
| wc -l
156
a new keyword is required :) ..
> In another mail I suggested
>
> optionally depends on FOO
>
> might be a better alternative than "uses".
>
>
how about just:
optional FOO
It is clear and easy to document ..
> BR,
> Jani.
>
next prev parent reply other threads:[~2020-04-21 4:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 1:11 [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword Saeed Mahameed
2020-04-17 1:11 ` [RFC PATCH 2/2] net/mlx5: Kconfig: Use "uses" instead of "imply" Saeed Mahameed
2020-04-17 8:08 ` Arnd Bergmann
2020-04-17 6:23 ` [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword Jani Nikula
2020-04-17 12:28 ` Jason Gunthorpe
2020-04-17 14:01 ` Jani Nikula
2020-04-17 14:07 ` Jason Gunthorpe
2020-04-17 10:24 ` Arnd Bergmann
2020-04-17 11:35 ` Saeed Mahameed
2020-04-18 19:00 ` Masahiro Yamada
2020-04-18 19:11 ` Nicolas Pitre
2020-04-18 20:07 ` Masahiro Yamada
2020-04-20 8:43 ` Jani Nikula
2020-04-20 18:42 ` Jakub Kicinski
2020-04-21 4:24 ` Saeed Mahameed [this message]
2020-04-21 13:58 ` Nicolas Pitre
2020-04-21 16:30 ` Saeed Mahameed
2020-04-21 18:23 ` Nicolas Pitre
2020-04-22 8:51 ` Jani Nikula
2020-04-22 21:13 ` Nicolas Pitre
2020-04-22 22:37 ` Randy Dunlap
2020-04-23 15:01 ` Nicolas Pitre
2020-04-23 15:05 ` Jason Gunthorpe
2020-04-23 15:11 ` Nicolas Pitre
2020-04-23 15:16 ` Jason Gunthorpe
2020-04-23 15:28 ` Arnd Bergmann
2020-04-23 15:33 ` Nicolas Pitre
2020-04-23 18:30 ` Jason Gunthorpe
2020-04-23 18:52 ` Nicolas Pitre
2020-04-20 13:53 ` Jason Gunthorpe
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