Build a fedora kernel rpm using docker and git checkouted sources instead of a src.rpm

README.md

Build a fedora kernel rpm

Rationale:

• I need a custom kernel (because sound won't work with vanilla)
• I want to use Fedora Atomic Host
• The only way to override the kernel with Fedora Atomic Host is to install a kernel package using ostree-rpm
• I have a metered network connection and want to avoid downloading the kernel sources too many times
• The powerful machine that can build the kernel is nor running Fedora or Red-hat based system with rpmbuild available

Start by creating a docker base image

You need the following Dockerfile in an empty directory:

FROM fedora:27

RUN dnf -y groupinstall 'Development Tools'
RUN dnf -y install fedora-packager
RUN dnf -y install rpmdevtools
RUN dnf -y install dnf-utils
RUN dnf -y install numactl-devel pesign
RUN dnf -y install sudo
RUN dnf builddep -y kernel
RUN dnf -y install flex bison

RUN sed -i.bak -n -e '/^Defaults.*requiretty/ { s/^/# /;};/^%wheel.*ALL$/ { s/^/# / ;} ;/^#.*wheel.*NOPASSWD/ { s/^#[ ]*//;};p' /etc/sudoers

RUN useradd -s /bin/bash -G adm,wheel,systemd-journal -m rpm
WORKDIR /home/rpm
USER rpm

RUN rpmdev-setuptree
WORKDIR /home/rpm/rpmbuild
RUN echo HOME=$HOME

Then, create a docker image by building it: docker build -t rpmbuild .

Clone the repository containing kernel.spec and update it

Clone the repository: git clone https://src.fedoraproject.org/git/rpms/kernel.git rpms-kernel

Update the kernel.spec according to your kernel version. in my case I have a kernel v4.14.24 and I want to suffix it with .4102.gec2d27324588.mildred (a chromiumos kernel):

-%global released_kernel 0
+%global released_kernel 1

-# define buildid .local
+%define buildid .4102.gec2d27324588.mildred

-%define base_sublevel 15
+%define base_sublevel 14

-%define stable_update 0
+%define stable_update 24

Then update the %build section to use .config instead of copying from configs/*, and avoid running make mrproper before the build if you want to save on some build time:

@@ -1226,14 +1226,15 @@ BuildKernel() {
 
     # and now to start the build process
 
-    make %{?make_opts} mrproper
-    cp configs/$Config .config
+    #make %{?make_opts} mrproper
+    #cp configs/$Config .config
 
     %if %{signkernel}%{signmodules}
     cp %{SOURCE11} certs/.
     %endif
 
     Arch=`head -1 .config | cut -b 3-`
+    Arch=x86_64
     echo USING ARCH=$Arch
 
     make %{?make_opts} ARCH=$Arch olddefconfig >/dev/null

(You need to manually specify the Arch because it may not be in the .config file)

Build your rpm

Run rpmbuild through docker:

mkdir -p BUILD/kernel-4.14.fc27 && \
docker run -ti --name=rpmbuild \
  -v $PWD/rpms-kernel/kernel.spec:/home/rpm/rpmbuild/SPECS/kernel.spec \
  -v $PWD/rpms-kernel:/home/rpm/rpmbuild/SOURCES \
  -v $PWD/RPMS:/home/rpm/rpmbuild/RPMS \
  -v $PWD/SRPMS:/home/rpm/rpmbuild/SRPMS \
  -v $PWD/BUILD:/home/rpm/rpmbuild/BUILD \
  -v $PWD/linux:/home/rpm/rpmbuild/BUILD/kernel-4.14.fc27/linux-4.14.24-1.4102.gec2d27324588.mildred.fc27.x86_64/ \
  -v /dev/zero:/home/rpm/rpmbuild/SOURCES/linux-4.14.tar.xz:ro \
  rpmbuild \
  rpmbuild -bb \
  --without debug --without doc --without perf --without tools --without debuginfo \
  --without kdump --without bootwrapper --without cross_headers \
  --nocheck --noclean --noprep \
  SPECS/kernel.spec

Here $PWD/linux contains the git checkout of the linux source tree. The name inside the container has to be adjusted too. $PWD/rpms-kernel is the checkout containing the kernel.spec you adjusted.

The BUILD/kernel-* directory must be owned by the rpm user inside the docker container so it won't fail after the build.