blob: 8d9b59c9bf124cf9642e3ef0491f73ea4f4fcef1 [file] [log] [blame]
# Class for generation of overlayfs mount units
# It's often desired in Embedded System design to have a read-only rootfs.
# But a lot of different applications might want to have a read-write access to
# some parts of a filesystem. It can be especially useful when your update mechanism
# overwrites the whole rootfs, but you want your application data to be preserved
# between updates. This class provides a way to achieve that by means
# of overlayfs and at the same time keeping the base rootfs read-only.
# Usage example.
# Set a mount point for a partition overlayfs is going to use as upper layer
# in your machine configuration. Underlying file system can be anything that
# is supported by overlayfs. This has to be done in your machine configuration.
# QA check fails to catch file existence if you redefine this variable in your recipe!
# OVERLAYFS_MOUNT_POINT[data] ?= "/data"
# The class assumes you have a data.mount systemd unit defined in your
# systemd-machine-units recipe and installed to the image.
# Then you can specify writable directories on a recipe base
# OVERLAYFS_WRITABLE_PATHS[data] = "/usr/share/my-custom-application"
# To support several mount points you can use a different variable flag. Assume we
# want to have a writable location on the file system, but not interested where the data
# survive a reboot. Then we could have a mnt-overlay.mount unit for a tmpfs file system:
# OVERLAYFS_MOUNT_POINT[mnt-overlay] = "/mnt/overlay"
# OVERLAYFS_WRITABLE_PATHS[mnt-overlay] = "/usr/share/another-application"
# Note: the class does not support /etc directory itself, because systemd depends on it
REQUIRED_DISTRO_FEATURES += "systemd overlayfs"
inherit systemd features_check
python do_create_overlayfs_units() {
CreateDirsUnitTemplate = """[Unit]
Description=Overlayfs directories setup
ExecStart=mkdir -p {DATA_MOUNT_POINT}/workdir{LOWERDIR} && mkdir -p {DATA_MOUNT_POINT}/upper{LOWERDIR}
MountUnitTemplate = """[Unit]
Description=Overlayfs mount unit
def prepareUnits(data, lower):
from oe.overlayfs import mountUnitName, helperUnitName
args = {
'DATA_MOUNT_UNIT': mountUnitName(data),
'CREATE_DIRS_SERVICE': helperUnitName(lower),
'LOWERDIR': lower,
with open(os.path.join(d.getVar('WORKDIR'), mountUnitName(lower)), 'w') as f:
with open(os.path.join(d.getVar('WORKDIR'), helperUnitName(lower)), 'w') as f:
overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT")
for mountPoint in overlayMountPoints:
for lower in d.getVarFlag('OVERLAYFS_WRITABLE_PATHS', mountPoint).split():
prepareUnits(d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint), lower)
# we need to generate file names early during parsing stage
python () {
from oe.overlayfs import strForBash, unitFileList
unitList = unitFileList(d)
for unit in unitList:
d.appendVar('SYSTEMD_SERVICE:' + d.getVar('PN'), ' ' + unit);
d.appendVar('FILES:' + d.getVar('PN'), ' ' + strForBash(unit))
d.setVar('OVERLAYFS_UNIT_LIST', ' '.join([strForBash(s) for s in unitList]))
do_install:append() {
install -d ${D}${systemd_system_unitdir}
for unit in ${OVERLAYFS_UNIT_LIST}; do
install -m 0444 ${WORKDIR}/${unit} ${D}${systemd_system_unitdir}
addtask create_overlayfs_units before do_install