initramfs support in Yocto

initramfs support in Yocto

[Luo Zhenhua-B19537]

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Hello all,

Does Yocto support initramfs build?


Best Regards,

Zhenhua


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Re: initramfs support in Yocto

[Darren Hart]

Hi Zhenhua,

On 03/02/2012 01:59 AM, Luo Zhenhua-B19537 wrote:
> Hello all,
> 
> Does Yocto support initramfs build?

Can you be more specific about what you are looking for? When you build
an image with the cpio.gz image type, you can boot that as an initramfs
with the following kernel command line:

initrd=core-image-minimal-fri2.cpio.gz root=/dev/ram0

If you are looking for something beyond that, please elaborate.

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel

Re: initramfs support in Yocto

[Jeremy Puhlman]

> Can you be more specific about what you are looking for? When you build
> an image with the cpio.gz image type, you can boot that as an initramfs
> with the following kernel command line:
>
> initrd=core-image-minimal-fri2.cpio.gz root=/dev/ram0
>
> If you are looking for something beyond that, please elaborate.
>

When most people refer to initramfs support it is compiling a built
image in to the kernel binary(e.g.  CONFIG_INITRAMFS_SOURCE).
INITRAMFS_IMAGE
is part of the kernel class that should enable that in the build.

Re: initramfs support in Yocto

[Joshua Immanuel]

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Hello Darren,

On Fri, 2012-03-02 at 08:06 -0800, Darren Hart wrote:
> Can you be more specific about what you are looking for? When you
> build an image with the cpio.gz image type, you can boot that as an
> initramfs 

I find that the cpio.gz image is created by running the following
command inside ${IMAGE_ROOTFS} directory

	find . | cpio -o -H newc | gzip -c -9 > <name>.rootfs.cpio.gz

Which means that the initramfs contains the entire rootfs filesystem
including the user space applications and its related libraries. In my
case, the size of initramfs comes to 158 MB gziped to 66 MB. Most of the
files in that are not needed for initramfs.

Is there any other way of reducing the initramfs size?

Moreover, I find in the bootimg.bbclass file that it uses the INITRD and
ROOTFS variables to generate the final hddimage. And these variables
usage is seen in image-live.bbclass. So, I guess I have to point the
INITRD variable (in my custom-image.bb recipe and inherit bootimg) to
core-image-minimal-initramfs generated file in deploy images directory.

The problem with this method is 

     1. It uses syslinux bootloader by default. I have to override this
        class (bootimg.bbclass) if I want to use something else like
        grub.
     2. I have to point the INITRD variable directly to the initramfs
        file in the deploy directory. (like
        ${DEPLOY_DIR_IMAGE}/core-image-minimal-initramfs-${MACHINE}.cpio.gz). But the cpio.gz extension is based on machine configuration. It can be cpio, cpio.gz, cpio.xz or cpio.lzma

This is what I inferred from the existing code. Am I completely in the
wrong direction?

Regards
Joshua
-- 
Joshua Immanuel
HiPro IT Solutions Private Limited
http://hipro.co.in

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Re: initramfs support in Yocto

[Paul Eggleton]

On Monday 05 March 2012 12:50:03 Joshua Immanuel wrote:
> Which means that the initramfs contains the entire rootfs filesystem
> including the user space applications and its related libraries. In my
> case, the size of initramfs comes to 158 MB gziped to 66 MB. Most of the
> files in that are not needed for initramfs.

The recommendation here would be to use a separate recipe to produce the 
intramfs image - we have an example of this in recipes-core/images/core-image-
minimal-initramfs.bb. This way you can fully control the content of the 
initramfs independent of your root filesystem.

Cheers,
Paul

-- 

Paul Eggleton
Intel Open Source Technology Centre