Rebuilding OLPC kernel

This document describes building an OLPC kernel from the olpc-2.6 git repository or SRPM. You will want to do this on a Fedora Core 6 machine.

The OLPC kernel sources

The first step involves grabbing the kernel sources; either do a 'git clone' of the kernel git repository, or install the kernel SRPM. Both steps are described on the Kernel page.

Installing the SRPM will place the sources in /usr/src/redhat/SOURCES/olpc-2.6.tar.bz2

Building the RPM (the easy way)

The simplest way to build the kernel RPM involves downloading the SRPM, installing it, and then running the rpmbuild command. The "dist", "olpc", and "head" macros should be defined when building:

• rpm -ivh kernel-2.6.*-20061026_dc5079fafb767e4olpc1.src.rpm
• rpmbuild -ba --define "dist olpc1" --define "olpc 1" --define "head dc5079fafb767e4" --target=i586 /usr/src/redhat/SPECS/olpc-2.6.spec

After the build finishes, the newly build RPMs will be in /usr/src/redhat/RPMS, and the build tree that was used will be in /usr/src/redhat/BUILD. To make quick changes to the source, for example you can:

# cd /usr/src/redhat/BUILD/kernel-2.6.18/linux-2.6.18.i586
# vi drivers/video/geode/gxfb_dcon.c
# make
# scp drivers/video/geode/gxfb_dcon.ko testboard:
# ssh testboard "rmmod gxfb_dcon; insmod ./gxfb_dcon.ko"

Building the RPM (from scratch)

This is the way that the official kernel RPMs are built. Note that this allows you to build within a subdirectory somewhere (rather than using /usr/src/redhat).

First, grab the kernel sources:

git clone --quiet git://dev.laptop.org/olpc-2.6 linux-2.6.22

Note that the name of the directory these sources are cloned into is important. It must start with linux.2.6., followed by two numbers identifying the sublevel. These must match the sublevel defined in olpc-2.6/Makefile. Optionally check out a particular branch using:

git checkout origin/stable

Now construct the build directory structure:

BASE=`pwd`/build; CUR=0
git clone --quiet git://dev.laptop.org/users/dilinger/olpc-2.6-rpm $BASE
(cd $BASE && mkdir -p BUILD  RPMS  SOURCES  SPECS  SRPMS)
tar -jc --exclude=.git -f $BASE/SOURCES/olpc-2.6.tar.bz2 linux-2.6.22

You need to build a config file for the kernel. This is done in the source directory checked out using git:

make ARCH=i386 -C linux-2.6.22 olpc_defconfig
cp linux-2.6.22/.config $BASE/SOURCES/kernel-olpc-custom.config

If building for a school server, make xs_defconfig instead:

make ARCH=i386 -C linux-2.6.22 xs_defconfig
cp linux-2.6.22/.config $BASE/SOURCES/kernel-olpc-custom.config

Now you can actually build the kernel and package it into an RPM:

rpmbuild -ba --define "dist 1.olpc" --define "olpc 1" --define "head `echo $CUR|cut -b1-15`" --target=i586 --define "_topdir $BASE" $BASE/SPECS/olpc-2.6.spec

The git://dev.laptop.org/users/dilinger/olpc-2.6-rpm repository contains the RPM SPEC file and other things necessary to bootstrap the RPM. When complete, the RPMs will be in build/RPMS/i586/.

Upgrading your kernel build

You will first need to pull down the newest kernel sources, and tar them up:

BASE=`pwd`/build; CUR=0
pushd linux-2.6.22; git pull ; popd
tar -jc --exclude=.git -f $BASE/SOURCES/olpc-2.6.tar.bz2 linux-2.6.22

You need to build a new config file for the kernel. This is done in the source directory checked out using git:

make ARCH=i386 -C linux-2.6.22 olpc_defconfig
cp linux-2.6.22/.config $BASE/SOURCES/kernel-olpc-custom.config

Don't forget to delete the directory from a previous build!

rm -r $BASE/BUILD/*

Now you can actually build the kernel and package it into an RPM:

rpmbuild -ba --define "dist 1.olpc" --define "olpc 1" --define "head `echo $CUR|cut -b1-15`" --target=i586 --define "_topdir $BASE" $BASE/SPECS/olpc-2.6.spec