Date:	Sun, 14 Sep 2014 22:05:46 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	mmarek@...e.cz, arnd@...db.de, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, oleg@...hat.com,
	grant.likely@...retlab.ca, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, ktkhai@...allels.com, sam@...nborg.org
Subject: Re: [PATCH 0/3] Implement /proc/built-in file similar to /proc/modules

On 14.09.2014 21:39, Greg KH wrote:
> On Sun, Sep 14, 2014 at 09:31:58PM +0400, Kirill Tkhai wrote:
>> On 14.09.2014 19:38, Greg KH wrote:
>>> On Sun, Sep 14, 2014 at 02:18:13PM +0400, Kirill Tkhai wrote:
>>>> This series implements a possibility to show the list of built-in drivers
>>>> to userspace. The names of drivers will be the same as when they are modules.
>>>
>>> Have you looked at /sys/modules/ ?  Doesn't that show what you want
>>> here?
>>
>> There are only the drivers in "/sys/module" which have parameters.
>> Drivers without parameters do not appear there.
> 
> Ah, didn't realize that.  Should be easy to fix though, if you really
> wanted to list the modules.  Much better than a random proc file that
> you have to parse :)

But it looks like one file is better than many new directories.
Furthermore some utils already may consider /sys/module directory as
a directory where all drivers have parameters. Is it good if we add
new ones of different type there?

>>>> So, if your system has "loop" driver then it appears either in /proc/modules
>>>> or in /proc/built-in and userspace will be able to know about this.
>>>>
>>>> Now this is impossible. The only way to get kernel configuration is
>>>> /proc/config.gz, but CONFIG_* names can change from time to time. Module
>>>> names are more or less standardized.
>>>
>>> Module names aren't "standardized", we change them at times when needed,
>>> just like CONFIG_ names.
>>>
>>> What is your end goal here?  As you say, config.gz is the real kernel
>>> configuration, just having a list of modules built in isn't going to
>>> help much in getting a working kernel config without it.
>>
>> It looks like userspace applications oriented on modules names rather
>> than on CONFIG_XXX parameters. /proc/config.gz is optional and userspace
>> applications can't base on it.
>>
>> For example, when I compile "loop" module built-in and "loop" is in
>> /etc/modules, init script warns about this module is not present and
>> can't be autoloaded. The script does not store CONFIG_XXX <-> module_xxx
>> conformity. And nobody stores it.
>>
>> When iptables wants extra functionality, it requests a module. Etc.
>>
>> Nobody is oriented on CONFIG_XXX parameters. It would be simple for
>> userspace to add a support of /proc/built-in analysing. It's very
>> similar to /proc/modules.
> 
> Shouldn't userspace focus on the functionality a module provides, not
> the module name itself?  Can't a test for the loop "module" just test to
> see if the loop control device is present?  Same for iptables (there's
> modprobe rules for iptable modules I think...)
> 
> In other words, don't focus on the module names, focus on the userspace
> function a module provides, there should always be a way to check that
> at run time (if not, then the module doesn't actually do much...)

Hm, I'm not sure that anybody stores CONFIG_XXX <-> module_xxx
conformity. Everybody bases on module name. If application is seeing
CONFIG_XXX=m, but the functionality, which it want's, is not available,
what it has to do? How should it convert CONFIG_XXX to module name?
So, many applications want module name instead of CONFIG_XXX, I believe.

Kirill
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