BYOK - Build Your Own Kernel
============================

What's this?
~~~~~~~~~~~~

In the BetterLinux releases for CentOS, some features are provided as
binary-only kernel modules. These modules cannot be used with custom kernels,
because binary compatibility across different kernel versions and
configurations is not guaranteed. Build-Your-Own-Kernel gives you the ability
to recompile the BetterLinux kernel modules for your own custom-built kernels.

How does it work?
~~~~~~~~~~~~~~~~~

Each BetterLinux kernel module is implemented as a binary-only part and some
open-source glue that provides a compatibility layer for the binary-only part
across different kernel versions and configurations. The binary-only part is
provided as a non-linked object file (.o) and the open-source part as a source
file (.c). When the whole module is recompiled on the client side, the
compatibility layer is built as usual and linked with the binary-only part.

Which kernels are supported
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Theoretically with BYOK all kernels are supported. However we can't test all
the potential kernels (especially if you are using custom patches).

In practice we support CentOS/RHEL 6.x and all LTS vanilla kernels running on CentOS/RHEL 6.x.
We will periodically update the betterlinux-byok RPM, so check if there's an update in our repos
before performing this process.  We will only support BYOK kernel patchsets for the kernels
they were designed for.

Example #1: build a BetterLinux kernel from a 3.14 vanilla kernel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following instructions document the steps to build a customized BetterLinux
kernel based on 3.14.27, on an otherwise CentOS 6.6 system.

- Create an account on the BetterLinux website (http://www.betterlinux.com/)
  and perform a standard installation.  You can later remove our stock CentOS
  kernel, although we recommend against it to ensure a stable environment
  while you establish your own kernel from our patchsets.

- Install our BYOK RPM

$ yum --disableexcludes=all install betterlinux-byok

- Download the Linux kernel source code from http://www.kernel.org/:

$ wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.14.27.tar.xz

- Extract the kernel source tarball:

$ tar xJf linux-3.14.27.tar.xz
$ cd linux-3.14.27

- Apply the corresponding BetterLinux patch:

$ patch -p1 < /etc/betterlinux/byok/patches/betterlinux-3.14-v1.2.3.patch

- Adjust your kernel .config (options required by BetterLinux are enabled by
default)

$ make menuconfig

- Build the custom BetterLinux kernel:

$ make

- Build the BetterLinux kernel modules:

$ rpmbuild --rebuild -D "kversion 3.14.27" -D "kbuilddir $PWD" \
/etc/betterlinux/byok/betterlinux-kernel-modules-1.2.3-1.src.rpm

- Install BetterLinux kernel:

$ sudo make modules_install
$ sudo new-kernel-pkg --make-default --host-only --mkinitrd --dracut --depmod --install 3.14.27

- Install BetterLinux kernel modules:

$ sudo rpm -ivh ~/rpmbuild/RPMS/x86_64/betterlinux-kernel-modules*

Example #2: build a BetterLinux kernel from a stock CentOS 6.6 kernel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Get the latest CentOS rpm from http://vault.centos.org

- Install the source rpm:

$ rpm -ivh kernel-2.6.32-504.3.3.el6.src.rpm

- Copy the all-in-one BetterLinux patch to your source rpm build directory:

$ cp betterlinux-centos6-2.6.32-504.3.3.el6-v1.2.3.patch ~/rpmbuild/SOURCES/

- Edit the stock kernel.spec file to apply the BetterLinux patch during the
kernel build process:

$ vi ~/rpmbuild/SPEC/kernel.spec

- Add the following line:

>>> Patch000001: betterlinux-centos6-2.6.32-504.3.3.el6-v1.2.3.patch

# empty final patch file to facilitate testing of kernel patches
Patch999999: linux-kernel-test.patch

- Add the following line (NOTE: must be before make configs):

>>> ApplyOptionalPatch betterlinux-centos6-2.6.32-504.3.3.el6-v1.2.3.patch

# Dynamically generate kernel .config files from config-* files
make -f %{SOURCE20} VERSION=%{version} configs

ApplyOptionalPatch linux-kernel-test.patch

- Recompile the kernel

$ cd ~/rpmbuild/SPEC
$ rpmbuild -bb --target=`uname -m` --with baseonly --without debug --without debuginfo --without kabichk kernel.spec

- Install kernel and kernel-devel packages:

$ cd ~/rpmbuild/RPMS/x86_64
$ sudo rpm -ivh kernel-2.6.32-504.3.3.el6.x86_64.rpm kernel-devel-2.6.32-504.3.3.el6.x86_64.rpm

- Build BetterLinux kernel modules (ignore git warnings):

$ rpmbuild --rebuild -D "kversion 2.6.32-504.3.3.el6.x86_64" betterlinux-kernel-modules-1.2.3-1.src.rpm

- Install BetterLinux kernel modules:

$ cd ~/rpmbuild/RPMS/x86_64
$ sudo rpm -ivh betterlinux-kernel-modules-1.2.3-1_2.6.32_504.3.3.el6.x86_64.rpm

- Reboot into the new BetterLinux kernel (2.6.32_504.3.3.el6.x86_64)

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