Automatically fetch and [cross] compile MPTCP for Raspberry Pi, yielding an easy-to-use install script.

rpi-mptcp-build.sh

#! /usr/bin/env bash

RPI_BRANCH=rpi-4.14.y
MPTCP_BRANCH=mptcp_v0.94

# For Pi 1, Pi 0, Pi 0 W, or Compute Module:
#KERNEL=kernel
#DEFCONFIG=bcmrpi_defconfig
# Or, for Pi 2, Pi 3, or Compute Module 3:
KERNEL=kernel7
DEFCONFIG=bcm2709_defconfig

sudo apt update && sudo apt install -y build-essential git bc

case $(uname -m) in
    *arm*)
    HOST=arm
    ;;
    *)
    HOST=$(uname -m)
    ;;
esac

if [ "$HOST" != "arm" ]; then
    git clone --depth 1 https://github.com/raspberrypi/tools rpi-tools
    if [ "$HOST" == "x86_64" ]; then
        export PATH=$PATH:$(pwd)/rpi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin
    else
        export PATH=$PATH:$(pwd)/rpi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin
    fi
fi

git clone -b $RPI_BRANCH --single-branch https://github.com/raspberrypi/linux.git
cd linux
git remote add -t $MPTCP_BRANCH mptcp https://github.com/multipath-tcp/mptcp.git
git fetch mptcp $MPTCP_BRANCH
git merge mptcp/$MPTCP_BRANCH -m "Merge $RPI_BRANCH and $MPTCP_BRANCH"

if [ "$?" -ne 0 ]; then
    echo "Merge was unsuccessful. Stopping."
    echo "Please resolve the conflict, commit, and then re-run the script."
    exit 1
fi

if [ "$HOST" != "arm" ]; then
    ARCH=arm
    CROSS_COMPILE=arm-linux-gnueabihf-
    MAKE_ARGS="ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE -j $(nproc)"
else
    MAKE_ARGS="-j $(nproc)"
fi

make $MAKE_ARGS $DEFCONFIG

tee << EOF > .config-mptcp
CONFIG_TCP_CONG_LIA=m
CONFIG_TCP_CONG_OLIA=m
CONFIG_TCP_CONG_WVEGAS=m
CONFIG_TCP_CONG_BALIA=m
CONFIG_IPV6=y
CONFIG_MPTCP=y
CONFIG_MPTCP_PM_ADVANCED=y
CONFIG_MPTCP_FULLMESH=y
CONFIG_MPTCP_NDIFFPORTS=m
CONFIG_MPTCP_BINDER=m
CONFIG_DEFAULT_FULLMESH=y
# CONFIG_DEFAULT_DUMMY is not set
CONFIG_DEFAULT_MPTCP_PM="fullmesh"
CONFIG_MPTCP_SCHED_ADVANCED=y
CONFIG_MPTCP_ROUNDROBIN=m
CONFIG_MPTCP_REDUNDANT=m
CONFIG_DEFAULT_SCHEDULER=y
CONFIG_DEFAULT_MPTCP_SCHED="default"
EOF

./scripts/kconfig/merge_config.sh -m .config .config-mptcp

make $MAKE_ARGS zImage modules dtbs

MOD_OUTPUT_DIR=output/
rm -rf $MOD_OUTPUT_DIR
mkdir -p $MOD_OUTPUT_DIR
make $MAKE_ARGS INSTALL_MOD_PATH=$MOD_OUTPUT_DIR modules_install

KERNEL_VERSION=$(ls output/lib/modules/)

rm $MOD_OUTPUT_DIR/lib/modules/$KERNEL_VERSION/build $MOD_OUTPUT_DIR/lib/modules/$KERNEL_VERSION/source

BOOT_DIR=output/boot
rm -rf $BOOT_DIR
mkdir -p $BOOT_DIR/overlays
cp arch/arm/boot/zImage $BOOT_DIR/$KERNEL.img
cp arch/arm/boot/dts/*.dtb $BOOT_DIR/
cp arch/arm/boot/dts/overlays/*.dtb* $BOOT_DIR/overlays/
cp arch/arm/boot/dts/overlays/README $BOOT_DIR/overlays/

tar -cvJf rpi-$KERNEL_VERSION-mptcp.tar.xz -C output/ .

tee << EOF > rpi-$KERNEL_VERSION-mptcp.sh
#! /usr/bin/env bash

if [ -z \$1 ]; then
    DIR=
else
    DIR=\$1
fi

TEMP_DIR=\$(mktemp -d)
cp \$DIR/boot/$KERNEL.img \$DIR/boot/$KERNEL-original.img
tail -n+16 \$BASH_SOURCE | tar -xvJf - -C \$TEMP_DIR
cp -R \$TEMP_DIR/* \$DIR/
rm -rf \$TEMP_DIR

exit 0
EOF

cat rpi-$KERNEL_VERSION-mptcp.tar.xz >> rpi-$KERNEL_VERSION-mptcp.sh
chmod a+x rpi-$KERNEL_VERSION-mptcp.sh

exactly what I was looking for. Thanks!
Hopefully MPTCP will make it into the kernel soon!!!

Is it working on latest RPI 4, and Rasbian Buster ?