add support for WSL2 kernels (#18)

Dockerfile

@@ -26,7 +26,14 @@ RUN apt-get install -y                                                       \
 # Linuxkit binaries (such as fixdep) require musl
 RUN apt-get install -y musl
 
-# Linuxkit requires the ability to copy data from docker images
+# Tar can fail sometimes on overlayfs, use bsdtar as a workaround
+RUN apt-get install -y bsdtar
+
+# Add required tools for those distros that require building the kernel from source
+RUN apt-get install -y build-essential libncurses-dev bison flex libssl-dev   \
+    libelf-dev
+
+# Some distros require the ability to copy data from docker images
 RUN apt-get -y install apt-transport-https \
      ca-certificates \
      curl \

src/build.sh

@@ -19,6 +19,9 @@ function get_kernel_type() {
     linuxkit)
         echo linuxkit
         ;;
+    microsoft-standard)
+        echo wsl
+        ;;
     *)
         case $KERNEL_UNAME in
         *Ubuntu*)

src/vanilla.sh

@@ -11,8 +11,8 @@ function get_kernel_src() {
     if [ ! -d /src/linux ]; then
         curl --retry 5 -o /src/linux-$version.tar.xz -L https://www.kernel.org/pub/linux/kernel/v${version%%.*}.x/linux-$version.tar.xz
         cd /src
-        tar xf linux-$version.tar.xz
-        mv $linux-version linux
+        bsdtar xf linux-$version.tar.xz
+        mv linux-$version linux
         rm linux-$version.tar.xz
     fi
 

src/wsl.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+#
+# Copyright The Titan Project Contributors.
+#
+
+#
+# Build process for the WSL2 (Windows Service for Linux 2) kernel. The kernel is
+# available at:
+#
+# https://github.com/microsoft/WSL2-Linux-Kernel
+#
+# However, there do not appear to be any pre-built binary packages, so we need
+# to fetch the kernel source and build it ourselves. Like the vanilla kernel
+# build process, we need a config.gz file to make sure we're building with the
+# appropriate kernel parameters.
+#
+
+# Get vanilla kernel source
+function get_kernel_src() {
+    local version=$KERNEL_VERSION
+
+    # Download Kernel source
+    if [ ! -d /src/linux ]; then
+        curl --retry 5 -o /src/$KERNEL_RELEASE.tar.gz -L https://github.com/microsoft/WSL2-Linux-Kernel/archive/$KERNEL_RELEASE.tar.gz
+        cd /src
+        bsdtar xf $KERNEL_RELEASE.tar.gz
+        mv WSL2-Linux-Kernel-$KERNEL_RELEASE linux
+        rm $KERNEL_RELEASE.tar.gz
+    fi
+
+    KERNEL_SRC=/src/linux
+    KERNEL_OBJ=/src/linux
+}
+
+#
+# Build the kernel from source. We need to do a full build because in order to build the ZFS
+# kernel modules, we not only depend on specific artifacts created in that process
+# (such as utsrelease.h), but we have to link against objects and we don't have
+# those objects available within the builder image.
+#
+function build_kernel() {
+    # Set kernel configuration
+    if [ ! -f /src/linux/.config ]; then
+        if [ -f /config/config.gz ]; then
+            zcat /config/config.gz > /src/linux/.config
+        else
+            zcat /proc/config.gz > /src/linux/.config
+        fi
+    fi
+
+    cd /src/linux && make -j8
+}
+
+# Vanilla entry point
+function build() {
+    get_zfs_source
+    if [ "$ZFS_CONFIG" != "user" ]; then
+    	get_kernel_src
+    	build_kernel
+    fi
+    build_zfs
+}