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

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Message-ID: <20140914173919.GA10059@kroah.com>
Date:	Sun, 14 Sep 2014 10:39:19 -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 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 :)

> >> 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...)

thanks,

greg k-h
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