linux-kernel - Re: [RFC PATCH 0/5] Add CONFIG symbol as module attribute

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Date:   Fri, 19 Aug 2016 11:07:36 +0200
From:   Michal Marek <mmarek@...e.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Cristina Moraru <cristina.moraru09@...il.com>,
        "vegard.nossum@...il.com" <vegard.nossum@...il.com>,
        Valentin Rothberg <valentinrothberg@...il.com>,
        Hannes Reinecke <hare@...e.de>, Sam Ravnborg <sam@...nborg.org>
Cc:     linux-kernel@...r.kernel.org, teg@...m.no, kay@...y.org,
        rusty@...tcorp.com.au, akpm@...ux-foundation.org,
        backports@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "rafael.j.wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Takashi Iwai <tiwai@...e.de>, Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Johannes Berg <johannes@...solutions.net>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Paul Bolle <pebolle@...cali.nl>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Sathya Prakash Veerichetty <sathya.prakash@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Laurence Oberman <loberman@...hat.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Tejun Heo <tj@...nel.org>,
        Jej B <James.Bottomley@...senpartnership.com>,
        Theodore Ts'o <tytso@....edu>, danijons@...dent.chalmers.se,
        Andrzej Wasowski <wasowski@....dk>
Subject: Re: [RFC PATCH 0/5] Add CONFIG symbol as module attribute

On 2016-08-18 19:55, Luis R. Rodriguez wrote:
> On Wed, Aug 17, 2016 at 09:26:58PM +0200, Cristina Moraru wrote:
> 
>> This patchset implements dynamic pegging of kconfig symbol
>> into driver modinfo section
> 
> First a little bit of motivation here helps, so let me try to
> help fill in some gaps. This may help explain what you have
> been working on a bit more.
> 
> First, for those that were not Cc'd but curious about this work
> so far, you can read the patches here:
> 
> Original cover letter:
> 
> https://lkml.kernel.org/r/1471462023-119645-1-git-send-email-cristina.moraru09@gmail.com
> 
> https://marc.info/?l=linux-kernel&m=147146213519750&w=2 - patch 1
> https://marc.info/?l=linux-kernel&m=147146209019744&w=2 - patch 2
> https://marc.info/?l=linux-kernel&m=147146211819747&w=2 - patch 3
> https://marc.info/?l=linux-kernel&m=147146209119745&w=2 - patch 4
> https://marc.info/?l=linux-kernel&m=147146209519746&w=2 - patch 5
> 
> There are a few situations in which you may want to extract a
> subset of Kconfig CONFIG_* symbols for a system. At least when
> only considering modules:
> 
>  a) When optimizing build requirements for a kernel for a system.
>     That is you boot into a distro kernel and then want to build
>     a slim kernel only with sensible kernel configuration options.
> 
>  b) When you are on a distribution kernel but the distribution
>     kernel provided lacks hardware support for your device, you
>     may either want to upgrade the full kernel in which case you
>     want to do a) or -- you may want to just a backports release
>     which provides just the modules you need, you'd use it on top
>     of the distribution kernel.

c) Having the mapping in sysfs would allow to simplify
streamline_config.pl avoid parsing Makefiles in perl. Only if the patch
did not depend on streamline_config.pl :). One idea would be to generate
the Module.ksymb in a similar way we generate the modules.builtin file:
Generate an alternate include/config/*.conf with all CONFIG_FOO=m
replaced with

CONFIG_FOO=m-CONFIG_FOO

and in the Makefile, iterate over $(filter m-CONFIG_%, $(.VARIABLES)) to
create the mapping. This would also properly cover cases where we build
the $(obj-m) list from another list. It would certainly create other
corner cases, but it's worth trying IMO.

Another thing is that we do not necessarily need to record this
information in .modinfo, but we can generate a list in
/lib/modules/`uname -r`/ for consumption. It could also include drivers
that are builtin in the current configuration.

Michal