rootfs: add alpine rootfs support

Fixes: #52
Signed-off-by: Peng Tao <bergwolf@gmail.com>

rootfs-builder/alpine/Dockerfile.in

@@ -0,0 +1,3 @@
+From golang:@GO_VERSION@-alpine3.7
+
+RUN apk update && apk add git make bash gcc musl-dev linux-headers apk-tools-static

rootfs-builder/alpine/config.sh

@@ -0,0 +1,23 @@
+# This is a configuration file add extra variables to
+# be used by build_rootfs() from rootfs_lib.sh the variables will be
+# loaded just before call the function.
+
+# Here there are a couple of variables you may need.
+# Remove them or add more
+
+# alpine version
+OS_VERSION=${OS_VERSION:-v3.7}
+
+# Essential base packages
+BASE_PACKAGES="alpine-base"
+
+# Alpine mirror to use
+# See a list of mirrors at http://nl.alpinelinux.org/alpine/MIRRORS.txt
+MIRROR=http://dl-5.alpinelinux.org/alpine
+
+# Default Architecture
+ARCH=${ARCH:-x86_64}
+
+# Mandatory Packages that must be installed
+#  - iptables: Need by Kata agent
+PACKAGES="iptables"

rootfs-builder/alpine/rootfs_lib.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+#
+# Copyright (c) 2018 HyperHQ Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+check_root()
+{
+	if [ "$(id -u)" != "0" ]; then
+		echo "Root is needed"
+		exit 1
+	fi
+}
+
+# - Arguments
+# rootfs_dir=$1
+#
+# - Optional environment variables
+#
+# EXTRA_PKGS: Variable to add extra PKGS provided by the user
+#
+# BIN_AGENT: Name of the Kata-Agent binary
+#
+# Any other configuration variable for a specific distro must be added
+# and documented on its own config.sh
+#
+# - Expected result
+#
+# rootfs_dir populated with rootfs pkgs
+# It must provide a binary in /sbin/init
+build_rootfs() {
+	# Mandatory
+	local ROOTFS_DIR=$1
+
+	# In case of support EXTRA packages, use it to allow
+	# users add more packages to the base rootfs
+	local EXTRA_PKGS=${EXTRA_PKGS:-}
+
+	# Populate ROOTFS_DIR
+	check_root
+	mkdir -p "${ROOTFS_DIR}"
+
+	/sbin/apk.static \
+	    -X ${MIRROR}/${OS_VERSION}/main \
+	    -U \
+	    --allow-untrusted \
+	    --root ${ROOTFS_DIR}\
+	    --initdb add ${BASE_PACKAGES} ${EXTRA_PKGS} ${PACKAGES}
+
+	mkdir -p ${ROOTFS_DIR}{/root,/etc/apk,/proc}
+	echo "${MIRROR}/${OS_VERSION}/main" >  ${ROOTFS_DIR}/etc/apk/repositories
+}

rootfs-builder/rootfs.sh

@@ -104,6 +104,7 @@ ENV PATH=\$PATH:\$GOROOT/bin:\$GOPATH/bin
 	pushd ${dir}
 	[ -f "${dockerfile_template}" ] || die "${dockerfile_template}: file not found"
 	sed \
+		-e "s|@GO_VERSION@|${GO_VERSION}|g" \
 		-e "s|@OS_VERSION@|${OS_VERSION}|g" \
 		-e "s|@INSTALL_GO@|${install_go//$'\n'/\\n}|g" \
 		${dockerfile_template} > Dockerfile
@@ -209,6 +210,7 @@ OK "Pull Agent source code"
 
 info "Build agent"
 pushd "${GOPATH}/src/${GO_AGENT_PKG}"
+make clean
 make INIT=${AGENT_INIT}
 make install DESTDIR="${ROOTFS_DIR}" INIT=${AGENT_INIT}
 popd