linux-kernel - Re: [PATCH 0/3] Implement /proc/built-in file similar to /proc/modules

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Date:	Sun, 14 Sep 2014 11:13:53 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
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 Sun, Sep 14, 2014 at 10:05:46PM +0400, Kirill Tkhai wrote:
> 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.

Why?

> 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?

What would break if you add new directories there with no parameters?

> >>>> 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?

Why would an application ever care about CONFIG_XXX at runtime?

> So, many applications want module name instead of CONFIG_XXX, I believe.

No, they want the functionality that a module provides, not the module
name, or some random configuation option.

It seems like you are trying to solve a problem that isn't there.  What
program is broken right now that this new proc file (or sysfs directory)
would fix?

thanks,

greg k-h
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