Rebuilding OLPC kernel

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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. These instructions do not work for FC8, but reportedly work on FC7.

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 built 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

Building a kernel module

From Problems compiling bluetooth module e-mail thread

Some hardware requires kernel support, such as a USB display or USB Bluetooth adapter. This may only involve adding a kernel module.

It's easiest to recompile the entire kernel and then use only the module you need from the build.

Steps

• determine the kernel your XO is using, for example if you are using kernel 2.6.25-20090223.1.olpc.69098d87d56945c, get the corresponding src.rpm from http://dev.laptop.org/~dilinger/testing/
• install kernel support packages and tools such as kernel-devel, kernel-headers, gcc, glibc, glibc-devel, glibc-headers and make.
• at the top level directory, run make menuconfig.
• enable what you need, for example navigate to Network > Bluetooth and Network > Bluetooth > Bluetooth Drivers.
  • when in doubt, turn it on — you don't have to put the module on your XO, but if you need it, you'd rather not build again.
• after saving your new config, type "make".

Sample commands

make ARCH=i386 INSTALL_MOD_STRIP=1 olpc_defconfig
make ARCH=i386 INSTALL_MOD_STRIP=1 menuconfig
activate bluetooth
make ARCH=i386 INSTALL_MOD_STRIP=1 modules
make ARCH=i386 INSTALL_MOD_STRIP=1 modules_install

See also the forum post Inserting a kernel module - the "easy way" HowTo