Message-Id: <20080401204247.068aaa22.sbrokenshire@xestia.co.uk>
Date:	Tue, 1 Apr 2008 20:42:47 +0100
From:	Steve Brokenshire <sbrokenshire@...tia.co.uk>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] Compress kernel modules on installation.

On Tue, 26 Feb 2008 12:28:40 +0100
Sam Ravnborg <sam@...nborg.org> wrote:

> On Mon, Feb 25, 2008 at 09:42:09PM +0000, Steve Brokenshire wrote:
> > Hi,
> > 
> > (I've sent this to the linux-kbuild and linux-kernel lists as this
> > patch modifies the Makefile.modinst file. I also don't subscribe to the 
> > linux-kbuild and linux-kernel mailing lists so can I have any replies
> > CC'ed to me please)
> > 
> > This patch allows kernel modules to be compressed when 'make
> > modules_install' is run after being copied to
> > the /lib/module/<version>/<...> directory which is useful if you have
> > module-init-tools installed with --enable-zlib. This patch adds an
> > option (MODULE_COMPRESS) to the kernel configuration file (specifically
> > init/Kconfig) so that the kernel modules will compressed if
> > MODULE_COMPRESS is set.
> > 
> > When MODULE_COMPRESS is set the output of 'make modules_install' will
> > go as the following:
> > 
> > INSTALL  drivers/fs/xfs/xfs.ko
> > COMPRESS drivers/fs/xfs/xfs.ko
> > INSTALL  drivers/fs/fat/fat.ko
> > COMPRESS drivers/fs/fat/fat.ko
> > ...
> > 
> > I've tested my patch on kernel versions 2.6.24.2, 2.6.24-git12, 2.6.23.14 and
> > 2.6.19 and they compile, install and compress into the respective
> > module directories without any errors.
> > 
> > I've also tested this with the uvcvideo (linux-uvc) kernel module (from
> > the SVN branch and with kernel versions 2.6.24.2, 2.6.24-git12, 2.6.23.14 and
> > 2.6.19) as that uses Kbuild properly when installing the module and
> > after installing the uvcvideo the module is then compressed.
> > Unfortunately, I couldn't find any other kernel modules which used the
> > Kbuild system for installing their kernel modules. :(
> > 
> > I've included include/config/auto.conf in Makefile.modinst so that it
> > can check if MODULE_COMPRESS is set when installing the kernel modules.
> 
> Should we mention this possibility in Documentation/kbuild/modules.txt also?
> 
> Otherwise from a quick scan it looks OK.
> As module-init-tols are our userspae counterpart we should align the
> functionality with that tool.
> I assume this gives us a simple choice of compression method and naming.
> 
> 	Sam

(Sorry for my lazy replying...)

I think it should be mentioned in Documentation/kbuild/modules.txt at
Chapter 2.2. The following should be added to the modules_install
target part:

If MODULES_COMPRESS is set when the modules_install target is run then
the module is compressed after it has been copied to 
/lib/modules/<kernel-version>. Compressed modules require 
module-init-tools installed with --zlib-enabled.

Does that sound right?

Anyway, as it currently is with the patch, MODULE_COMPRESS isn't as scalable as it perhaps could be and I've been thinking I should try and make a better version of the patch which is scalable (So depending on how module-init-tools is updated in the future each option would also give which version of module-init-tools is required to use that compression method in the init/KConfig file)

Steve
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