add layer meta-netboot to enable network boot over NBD (Network Block Device)

To enable the build of network bootable images, the following line must be
added to conf/local.conf:

   INHERIT += "netboot"

This layer contains recipes for the following components:
* busybox: activate the built-in NBD client
* initramfs-netboot: contains the init script started by the kernel,
  responsible for mounting the remote root filesystem then pivoting and
  exec'ing systemd
* initramfs-netboot-image: image to specify for building the initrd

More details are available in meta-netboot/README.

Bug-AGL: SPEC-175

Change-Id: Id2328dd9233d238cde77311e64e58344be244988
Signed-off-by: Stephane Desneux <stephane.desneux@iot.bzh>

2 files changed, 168 insertions, 0 deletions

diff --git a/meta-netboot/recipes-core/initramfs-netboot/files/init.sh b/meta-netboot/recipes-core/initramfs-netboot/files/init.sh
new file mode 100644
index 000000000..dae9a85cb
--- /dev/null
+++ b/meta-netboot/recipes-core/initramfs-netboot/files/init.sh
@@ -0,0 +1,149 @@
+#!/bin/sh
+
+################################################################################
+#
+# Init script to boot over network through NBD
+#
+# Contact: Stéphane Desneux <stephane.desneux@iot.bzh>
+#
+################################################################################
+
+# banner generator: echo "AGL - Netboot" | figlet -f slant -w 80 -c
+cat <<'EOF' >&2
+________________________________________________________________________________
+         ___   ________                _   __     __  __                __
+        /   | / ____/ /               / | / /__  / /_/ /_  ____  ____  / /_
+       / /| |/ / __/ /      ______   /  |/ / _ \/ __/ __ \/ __ \/ __ \/ __/
+      / ___ / /_/ / /___   /_____/  / /|  /  __/ /_/ /_/ / /_/ / /_/ / /_
+     /_/  |_\____/_____/           /_/ |_/\___/\__/_.___/\____/\____/\__/
+________________________________________________________________________________
+EOF
+
+# global variables
+
+SMACK=n
+NBD_SERVER=
+NBD_PORT=10809
+NBD_DEV=/dev/nbd0
+DEBUG=n
+
+# -------------------------------------------
+
+log_info() { echo "$0[$$]: $@" >&2; }
+log_error() { echo "$0[$$]: ERROR $@" >&2; }
+
+do_mount_fs() {
+	log_info "mounting FS: $@"
+	[[ -e /proc/filesystems ]] && { grep -q "$1" /proc/filesystems || { log_error "Unknown filesystem"; return 1; } }
+	[[ -d "$2" ]] || mkdir -p "$2"
+	[[ -e /proc/mounts ]] && { grep -q -e "^$1 $2 $1" /proc/mounts && { log_info "$2 ($1) already mounted"; return 0; } }
+	mount -t "$1" "$1" "$2"
+}
+
+bail_out() {
+	log_error "$@"
+	check_debug "Reboot will occur after exiting this shell."
+	log_info "Rebooting..."
+	exec reboot -f
+}
+
+check_debug() {
+	case $DEBUG in
+		Y|y|yes|1|true)
+			log_info "$@"
+			/bin/sh -i
+			;;
+	esac
+}
+
+# -------------------------------------------
+
+export PATH=/sbin:/usr/sbin:/bin:/usr/bin
+
+log_info "starting initrd script"
+
+do_mount_fs proc /proc
+do_mount_fs sysfs /sys
+do_mount_fs devtmpfs /dev
+do_mount_fs devpts /dev/pts
+do_mount_fs tmpfs /dev/shm
+do_mount_fs tmpfs /tmp
+do_mount_fs tmpfs /run
+
+# parse kernel commandline to get NBD server
+for x in $(cat /proc/cmdline); do
+	case $x in
+		nbd.server=*) NBD_SERVER=${x/*=/};;
+		nbd.port=*) NBD_PORT=${x/*=/};;
+		nbd.dev=*)  NBD_DEV=/dev/${x/*=/};;
+		nbd.debug=*) DEBUG=${x/*=/};;
+	esac
+done
+
+check_debug "Debug point 1. Exit to continue initrd script (mount NBD device)."
+
+log_info "NBD parameters: device $NBD_DEV, server $NBD_SERVER:$NBD_PORT"
+
+# check if smack is active (and if so, mount smackfs)
+grep -q smackfs /proc/filesystems && {
+	SMACK=y
+
+	do_mount_fs smackfs /sys/fs/smackfs
+
+	# adjust current label and network label
+	echo System >/proc/self/attr/current
+	echo System >/sys/fs/smackfs/ambient
+}
+
+# start nbd client
+try=5
+while :;do
+	log_info "Starting NBD client"
+	nbd-client $NBD_SERVER $NBD_PORT $NBD_DEV && { log_info "NBD client successfully started"; break; }
+	log_info "NBD client failed"
+	[[ $try -gt 0 ]] && { log_info "Retrying ($try trie(s) left)..."; sleep 3; try=$(( try - 1 )); continue; }
+
+	bail_out "Unable to mount NBD device $NBD_DEV using server $NBD_SERVER:$NBD_PORT"
+done
+
+# mount NBD device
+mkdir -p /sysroot
+mount $NBD_DEV /sysroot || bail_out "Unable to mount root NBD device"
+
+# move mounted devices to new root
+cd /sysroot
+for x in dev proc sys tmp run; do
+	log_info "Moving /$x to new rootfs"
+	mount -o move /$x $x
+done
+
+# switch to new rootfs
+log_info "Switching to new rootfs"
+mkdir -p run/initramfs
+pivot_root . run/initramfs || bail_out "pivot_root failed."
+
+# workaround for connman (avoid bringing down the network interface used for booting)
+if [[ -f /lib/systemd/system/connman.service ]]; then
+	log_info "Adjusting Connman configuration"
+	iface=$(ip -o link show up | tr ':' ' ' | awk '{print $2}' | grep -v -e "^lo$" | head -1)
+	sed -i "s|connmand -n\$|connmand -n -I $iface|g" /lib/systemd/system/connman.service
+fi
+
+# finally, run systemd
+check_debug "Debug point 2. Exit to continue initrd script (run systemd)."
+
+log_info "Exec'ing systemd"
+# banner generator: echo "AGL Booting . . ." | figlet -f slant -w 80 -c
+cat <<'EOF' >&2
+________________________________________________________________________________
+      ___   ________       ____              __  _
+     /   | / ____/ /      / __ )____  ____  / /_(_)___  ____ _
+    / /| |/ / __/ /      / __  / __ \/ __ \/ __/ / __ \/ __ `/
+   / ___ / /_/ / /___   / /_/ / /_/ / /_/ / /_/ / / / / /_/ /   _     _     _
+  /_/  |_\____/_____/  /_____/\____/\____/\__/_/_/ /_/\__, /   (_)   (_)   (_)
+_____________________________________________________/____/_____________________
+EOF
+
+exec /lib/systemd/systemd </dev/console >/dev/console 2>&1
+bail_out
+
diff --git a/meta-netboot/recipes-core/initramfs-netboot/initramfs-netboot_1.0.bb b/meta-netboot/recipes-core/initramfs-netboot/initramfs-netboot_1.0.bb
new file mode 100644
index 000000000..5c85bee8f
--- /dev/null
+++ b/meta-netboot/recipes-core/initramfs-netboot/initramfs-netboot_1.0.bb
@@ -0,0 +1,19 @@
+SUMMARY = "Extremely basic live image init script"
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
+SRC_URI = "file://init.sh"
+
+S = "${WORKDIR}"
+
+do_install() {
+	install -dm 0755 ${D}/etc
+	touch ${D}/etc/initrd-release
+	install -dm 0755 ${D}/dev
+	install -dm 0755 ${D}/sbin
+        install -m 0755 ${WORKDIR}/init.sh ${D}/sbin/init
+}
+
+inherit allarch
+
+FILES_${PN} += " /dev /etc/initrd-release /sbin/init "
+