rootfs-builder: support provisioning existing rootfs

Add the use case of provisioning an existing rootfs directory with the
components / configurations needed to generate a Kata compatible images.
This supports use cases such as using a rootfs built outside of
osbuilder, and providing a overlay for dracut built initrds.

Signed-off-by: Marco Vedovati <mvedovati@suse.com>

rootfs-builder/README.md

@@ -1,4 +1,8 @@
+* [Building a Guest OS rootfs for Kata Containers](#building-a-guest-os-rootfs-for-kata-containers)
   * [Supported base OSs](#supported-base-oss)
+     * [Extra features](#extra-features)
+        * [Supported distributions list](#supported-distributions-list)
+        * [Generate Kata specific files](#generate-kata-specific-files)
   * [Rootfs requirements](#rootfs-requirements)
   * [Creating a rootfs](#creating-a-rootfs)
   * [Creating a rootfs with kernel modules](#creating-a-rootfs-with-kernel-modules)
@@ -21,10 +25,25 @@ The `rootfs.sh` script builds a rootfs based on a particular Linux\*
 distribution. The script supports multiple distributions and can be extended
 to add further ones.
 
-To list the supported distributions, run:
+### Extra features
-
+#### Supported distributions list
+Supported distributions can be listed with:
 ```
-$ ./rootfs.sh -h
+$ ./rootfs.sh -l
+```
+
+#### Generate Kata specific files
+`rootfs.sh` can be used to only populate a target directory with the set of Kata
+specific files and components integrable into a generic Linux rootfs to generate
+a Kata guest OS image.
+This feature can be used when creating a rootfs with a distribution not officially
+supported by osbuilder.
+It is also used when building the rootfs using the 'dracut' build method.
+
+To obtain this, simply invoke `rootfs.sh` without specifying a target rootfs, e.g.:
+```
+mkdir kata-overlay
+./rootfs.sh -r `pwd`/kata-overlay
 ```
 
 ## Rootfs requirements

rootfs-builder/rootfs.sh

@@ -52,18 +52,31 @@ typeset -r CONFIG_ARCH_SH="config_${ARCH}.sh"
 # build_rootfs() function.
 typeset -r LIB_SH="rootfs_lib.sh"
 
+# rootfs distro name specified by the user
+typeset distro=
+
+# Absolute path to the rootfs root folder
+typeset ROOTFS_DIR
+
+# Absolute path in the rootfs to the "init" executable / symlink.
+# Typically something like "${ROOTFS_DIR}/init
+typeset init=
+
 #$1: Error code if want to exit different to 0
 usage()
 {
 	error="${1:-0}"
 	cat <<EOT
 
-Usage: ${script_name} [options] <distro>
+Usage: ${script_name} [options] [DISTRO]
 
-Build a rootfs based on <distro> OS, to be included in a Kata Containers
+Build and setup a rootfs directory based on DISTRO OS, used to create
-image.
+Kata Containers images or initramfs.
 
-Supported <distro> values:
+When no DISTRO is provided, an existing base rootfs at ROOTFS_DIR is provisioned
+with the Kata specific components and configuration.
+
+Supported DISTRO values:
 $(get_distros | tr "\n" " ")
 
 Options:
@@ -75,7 +88,7 @@ Options:
                     yaml description.
   -r <directory>    Specify the rootfs base directory. Overrides the ROOTFS_DIR
                     environment variable.
-  -t                Print the test configuration for <distro> and exit
+  -t DISTRO         Print the test configuration for DISTRO and exit
                     immediately.
 
 Environment Variables:
@@ -100,7 +113,7 @@ DISTRO_REPO         Use host repositories to install guest packages.
 GO_AGENT_PKG        URL of the Git repository hosting the agent package.
                     Default value: ${GO_AGENT_PKG}
 
-GRACEFUL_EXIT       If set, and if the <distro> configuration specifies a
+GRACEFUL_EXIT       If set, and if the DISTRO configuration specifies a
                     non-empty BUILD_CAN_FAIL variable, do not return with an
                     error code in case any of the build step fails.
                     This is used when running CI jobs, to tolerate failures for
@@ -112,7 +125,7 @@ KERNEL_MODULES_DIR  Path to a directory containing kernel modules to include in
                     Default value: <empty>
 
 ROOTFS_DIR          Path to the directory that is populated with the rootfs.
-                    Default value: <${script_name} path>/rootfs-<distro-name>
+                    Default value: <${script_name} path>/rootfs-<DISTRO-name>
 
 USE_DOCKER          If set, build the rootfs inside a container (requires
                     Docker).
@@ -137,7 +150,9 @@ get_distros() {
 }
 
 get_test_config() {
-	local distro="$1"
+	local -r distro="$1"
+	[ -z "$distro" ] && die "No distro name specified"
+
 	local config="${script_dir}/${distro}/config.sh"
 	source ${config}
 
@@ -330,20 +345,8 @@ compare_versions()
 	true
 }
 
-while getopts a:hlo:r:t: opt
+check_env_variables()
-do
+{
-	case $opt in
-		a)	AGENT_VERSION="${OPTARG}" ;;
-		h)	usage ;;
-		l)	get_distros | sort && exit 0;;
-		o)	OSBUILDER_VERSION="${OPTARG}" ;;
-		r)	ROOTFS_DIR="${OPTARG}" ;;
-		t)	get_test_config "${OPTARG}" && exit 0;;
-	esac
-done
-
-shift $(($OPTIND - 1))
-
 	# Fetch the first element from GOPATH as working directory
 	# as go get only works against the first item in the GOPATH
 	[ -z "$GOPATH" ] && die "GOPATH not set"
@@ -353,10 +356,12 @@ GOPATH_LOCAL="${GOPATH%%:*}"
 
 	[ -n "${KERNEL_MODULES_DIR}" ] && [ ! -d "${KERNEL_MODULES_DIR}" ] && die "KERNEL_MODULES_DIR defined but is not an existing directory"
 
-[ -z "${OSBUILDER_VERSION}" ] && die "need osbuilder version"
+	[ -n "${OSBUILDER_VERSION}" ] || die "need osbuilder version"
-
+}
-distro="$1"
 
+# Builds a rootfs based on the distro name provided as argument
+build_rootfs_distro()
+{
 	[ -n "${distro}" ] || usage 1
 	distro_config_dir="${script_dir}/${distro}"
 
@@ -376,8 +381,6 @@ if [ -z "$ROOTFS_DIR" ]; then
 		 ROOTFS_DIR="${script_dir}/rootfs-${OS_NAME}"
 	fi
 
-init="${ROOTFS_DIR}/sbin/init"
-
 	if [ -e "${distro_config_dir}/${LIB_SH}" ];then
 		rootfs_lib="${distro_config_dir}/${LIB_SH}"
 		info "rootfs_lib.sh file found. Loading content"
@@ -471,13 +474,31 @@ else
 	fi
 
 	build_rootfs ${ROOTFS_DIR}
+}
+
+# Used to create a minimal directory tree where the agent can be instaleld.
+# This is used when a distro is not specified.
+prepare_overlay()
+{
 	pushd "${ROOTFS_DIR}" >> /dev/null
-if [ "$PWD" != "/" ] ; then
+	mkdir -p ./etc ./lib/systemd ./sbin ./var
-	rm -rf ./var/cache/ ./var/lib ./var/log
+	ln -sf  ./usr/lib/systemd/systemd ./init
-fi
+	ln -sf  ../../init ./lib/systemd/systemd
+	ln -sf  ../init ./sbin/init
+	popd  >> /dev/null
+}
+
+# Setup an existing rootfs directory, based on the OPTIONAL distro name
+# provided as argument
+setup_rootfs()
+{
+	[ -z "$distro" ] && prepare_overlay
 
 	info "Create symlink to /tmp in /var to create private temporal directories with systemd"
-rm -rf ./var/tmp
+	pushd "${ROOTFS_DIR}" >> /dev/null
+	if [ "$PWD" != "/" ] ; then
+		rm -rf ./var/cache/ ./var/lib ./var/log ./var/tmp
+	fi
 	ln -s ../tmp ./var/
 
 	# For some distros tmp.mount may not be installed by default in systemd paths
@@ -493,7 +514,7 @@ popd  >> /dev/null
 	[ -n "${KERNEL_MODULES_DIR}" ] && copy_kernel_modules ${KERNEL_MODULES_DIR} ${ROOTFS_DIR}
 
 	chrony_conf_file="${ROOTFS_DIR}/etc/chrony.conf"
-if [ ${distro} == ubuntu ] || [ ${distro} == debian ] ; then
+	if [ "${distro}" == "ubuntu" ] || [ "${distro}" == "debian" ] ; then
 		chrony_conf_file="${ROOTFS_DIR}/etc/chrony/chrony.conf"
 	fi
 
@@ -512,18 +533,9 @@ EOT
 	# Reference:  https://chrony.tuxfamily.org/doc/3.4/chrony.conf.html
 	sed -i 's/^\(server \|pool \|peer \)/# &/g'  ${chrony_conf_file}
 
-chrony_systemd_service="${ROOTFS_DIR}/usr/lib/systemd/system/chronyd.service"
-if [ ${distro} == ubuntu ] || [ ${distro} == debian ] ; then
-	chrony_systemd_service="${ROOTFS_DIR}/lib/systemd/system/chrony.service"
-fi
-
-if [ -f "$chrony_systemd_service" ]; then
-	sed -i '/^\[Unit\]/a ConditionPathExists=\/dev\/ptp0' ${chrony_systemd_service}
-fi
-
 	# The CC on s390x for fedora needs to be manually set to gcc when the golang is downloaded from the main page.
 	# See issue: https://github.com/kata-containers/osbuilder/issues/217
-[ "$distro" == fedora ] && [ "$ARCH" == "s390x" ] && export CC=gcc
+	[ "$distro" == "fedora" ] && [ "$ARCH" == "s390x" ] && export CC=gcc
 
 	AGENT_DIR="${ROOTFS_DIR}/usr/bin"
 	AGENT_DEST="${AGENT_DIR}/${AGENT_BIN}"
@@ -556,3 +568,41 @@ OK "init is installed"
 
 	info "Creating summary file"
 	create_summary_file "${ROOTFS_DIR}"
+}
+
+parse_arguments()
+{
+	while getopts a:hlo:r:t: opt
+	do
+		case $opt in
+			a)	AGENT_VERSION="${OPTARG}" ;;
+			h)	usage ;;
+			l)	get_distros | sort && exit 0;;
+			o)	OSBUILDER_VERSION="${OPTARG}" ;;
+			r)	ROOTFS_DIR="${OPTARG}" ;;
+			t)	get_test_config "${OPTARG}" && exit -1;;
+			*)  die "Found an invalid option";;
+		esac
+	done
+
+	shift $(($OPTIND - 1))
+	distro="$1"
+}
+
+main()
+{
+	parse_arguments $*
+	check_env_variables
+	init="${ROOTFS_DIR}/sbin/init"
+
+	if [ -n "$distro" ]; then
+		build_rootfs_distro
+	else
+		#Make sure ROOTFS_DIR is set correctly
+		[ -d "${ROOTFS_DIR}" ] || die "Invalid rootfs directory: '$ROOTFS_DIR'"
+	fi
+
+	setup_rootfs
+}
+
+main $*