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Date: Tue, 26 Feb 2008 11:14:55 +0200
From: Adrian Bunk <bunk@kernel.org>
To: Willy Tarreau <w@1wt.eu>
Cc: Steve Brokenshire <sbrokenshire@xestia.co.uk>,
       linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org
Subject: Re: [PATCH] Compress kernel modules on installation.
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On Mon, Feb 25, 2008 at 11:21:38PM +0100, Willy Tarreau 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.
> > 
> > Unfortunately when I ran mkinitrd (CentOS version) to create the initrd
> > image to go with the kernel, I get errors saying that certain kernel
> > modules don't exist despite the fact they do actually exist. When I
> > pass --allow-missing to mkinitrd, it seems to go fine but when booting
> > up with the system with the new initrd image I get error messages
> > saying that the modules don't exist.
> > 
> > A workaround is to compile the modules, don't have MODULE_COMPRESS set 
> > in .config, install the modules, run mkinitrd and copy it to /boot, set 
> > MODULE_COMPRESS in .config and then install the modules again but
> > compressed.
> > 
> > That's about it really. The only showstopper I feel is mkinitrd not
> > working properly with the compressed kernel modules.
> 
> Have you tried keeping the module names intact (.ko, not .ko.gz) ?
> It's what I was doing with modutils in 2.4 and what I'm still doing
> with module-init-tools in 2.6. While I don't particularly use mkinitrd,
> I think that keeping the name intact is preferable and should help.

How would you see if, and if yes with what program, a module was 
compressed if the name is kept intact?

I'd assume stuff like mkinitrd simply also needs to gain knowledge about 
compressed modules.

> Regards,
> Willy

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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