[Buildroot] Question about kernel defconfig

[Buildroot] Question about kernel defconfig

[Thomas Petazzoni]

Hello Sam,

I am currently working on cleaning up how Buildroot handles board
configuration [1]. As part of this clean up, I'd like to move away from
full kernel .config files and instead use minimal kernel configs (only
non-default options are stored, the kernel configuration files are
produced with savedefconfig).

So, for example for the Qemu Versatile platform, I have the kernel
configuration file visible at
http://git.buildroot.net/~tpetazzoni/git/buildroot/tree/board/qemu/arm-versatile/linux-2.6.36.config?h=for-2010.11/boards-cleanup&id=8033fd6cbacfa96a3bcfce74caad8c423bf60cd1.

When Buildroot configures the kernel, it simply copies the given kernel
configuration file to .config into the kernel source tree. See
http://git.buildroot.net/buildroot/tree/linux/linux.mk#n89.

Unfortunately, with those minimal configuration files, the kernel
"Restart config" and then asks interactively for the value of all
options not specificied in the minimal configuration file.

I'd like to have the same behaviour the kernel has when using its own
internal defconfigs files from arch/$(ARCH)/configs. Is this possible ?
Did I miss something totally obvious ?

Thanks,

Thomas

[1]
http://git.buildroot.net/~tpetazzoni/git/buildroot/log/?h=for-2010.11/boards-cleanup
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

[Buildroot] Question about kernel defconfig

[Sam Ravnborg]

On Mon, Nov 22, 2010 at 06:33:27PM +0100, Thomas Petazzoni wrote:
> Hello Sam,
> 
> I am currently working on cleaning up how Buildroot handles board
> configuration [1]. As part of this clean up, I'd like to move away from
> full kernel .config files and instead use minimal kernel configs (only
> non-default options are stored, the kernel configuration files are
> produced with savedefconfig).
> 
> So, for example for the Qemu Versatile platform, I have the kernel
> configuration file visible at
> http://git.buildroot.net/~tpetazzoni/git/buildroot/tree/board/qemu/arm-versatile/linux-2.6.36.config?h=for-2010.11/boards-cleanup&id=8033fd6cbacfa96a3bcfce74caad8c423bf60cd1.
> 
> When Buildroot configures the kernel, it simply copies the given kernel
> configuration file to .config into the kernel source tree. See
> http://git.buildroot.net/buildroot/tree/linux/linux.mk#n89.
> 
> Unfortunately, with those minimal configuration files, the kernel
> "Restart config" and then asks interactively for the value of all
> options not specificied in the minimal configuration file.
> 
> I'd like to have the same behaviour the kernel has when using its own
> internal defconfigs files from arch/$(ARCH)/configs. Is this possible ?

kconfig behaves in different ways depending on what type of input it receives.
To use the minimal configs generated by "savedefconfig" you need to read
them using "--defconfig".
And there is today no way to specify your own defconfig file.

One workaround could be to copy the file to:

   arch/$ARCH/configs/buildroot_defconfig

And then use:

    make buildroot_defconfig

This will read the minimal config in the same way the kernel usually does it.

You can also experiment with calling scripts/kconfig/conf --defconfig foobar arch/$ARCH/Kconfig
But I think the solution where you use buildroot_defconfig is the easiest
to maintain.

	Sam

[Buildroot] Question about kernel defconfig

[Thomas Petazzoni]

Hello,

On Mon, 22 Nov 2010 22:33:18 +0100
Sam Ravnborg <sam@ravnborg.org> wrote:

> kconfig behaves in different ways depending on what type of input it receives.
> To use the minimal configs generated by "savedefconfig" you need to read
> them using "--defconfig".
> And there is today no way to specify your own defconfig file.
> 
> One workaround could be to copy the file to:
> 
>    arch/$ARCH/configs/buildroot_defconfig
> 
> And then use:
> 
>     make buildroot_defconfig
> 
> This will read the minimal config in the same way the kernel usually does it.

Ok, thanks. I thought about this in the past, but found it a bit hacky.
But as there's no other simple solution, I just implemented that.

Thanks!

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com