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#
# Copyright OpenEmbedded Contributors
#
# SPDX-License-Identifier: MIT
#
# 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"
#
# Per default the class assumes you have a corresponding fstab entry or systemd
# mount unit (data.mount in this case) for this mount point installed on the
# image, for instance via a wks script or the systemd-machine-units recipe.
#
# If the mount point is handled somewhere else, e.g. custom boot or preinit
# scripts or in a initramfs, then this QA check can be skipped by adding
# mount-configured to the related OVERLAYFS_QA_SKIP flag:
#
# OVERLAYFS_QA_SKIP[data] = "mount-configured"
#
# To use the overlayfs, you just have to specify writable directories inside
# their recipe:
#
# 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"
#
# If your recipe deploys a systemd service, then it should require and be
# started after the ${PN}-overlays.service to make sure that all overlays are
# mounted beforehand.
#
# Note: the class does not support /etc directory itself, because systemd depends on it
# For /etc directory use overlayfs-etc class
REQUIRED_DISTRO_FEATURES += "systemd overlayfs"
inherit systemd features_check
OVERLAYFS_CREATE_DIRS_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-create-dirs.service.in"
OVERLAYFS_MOUNT_UNIT_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-unit.mount.in"
OVERLAYFS_ALL_OVERLAYS_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-all-overlays.service.in"
python do_create_overlayfs_units() {
from oe.overlayfs import mountUnitName
with open(d.getVar("OVERLAYFS_CREATE_DIRS_TEMPLATE"), "r") as f:
CreateDirsUnitTemplate = f.read()
with open(d.getVar("OVERLAYFS_MOUNT_UNIT_TEMPLATE"), "r") as f:
MountUnitTemplate = f.read()
with open(d.getVar("OVERLAYFS_ALL_OVERLAYS_TEMPLATE"), "r") as f:
AllOverlaysTemplate = f.read()
def prepareUnits(data, lower):
from oe.overlayfs import helperUnitName
args = {
'DATA_MOUNT_POINT': data,
'DATA_MOUNT_UNIT': mountUnitName(data),
'CREATE_DIRS_SERVICE': helperUnitName(lower),
'LOWERDIR': lower,
}
bb.debug(1, "Generate systemd unit %s" % mountUnitName(lower))
with open(os.path.join(d.getVar('WORKDIR'), mountUnitName(lower)), 'w') as f:
f.write(MountUnitTemplate.format(**args))
bb.debug(1, "Generate helper systemd unit %s" % helperUnitName(lower))
with open(os.path.join(d.getVar('WORKDIR'), helperUnitName(lower)), 'w') as f:
f.write(CreateDirsUnitTemplate.format(**args))
def prepareGlobalUnit(dependentUnits):
from oe.overlayfs import allOverlaysUnitName
args = {
'ALL_OVERLAYFS_UNITS': " ".join(dependentUnits),
'PN': d.getVar('PN')
}
bb.debug(1, "Generate systemd unit with all overlays %s" % allOverlaysUnitName(d))
with open(os.path.join(d.getVar('WORKDIR'), allOverlaysUnitName(d)), 'w') as f:
f.write(AllOverlaysTemplate.format(**args))
mountUnitList = []
overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT")
for mountPoint in overlayMountPoints:
bb.debug(1, "Process variable flag %s" % mountPoint)
for lower in d.getVarFlag('OVERLAYFS_WRITABLE_PATHS', mountPoint).split():
bb.debug(1, "Prepare mount unit for %s with data mount point %s" %
(lower, d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint)))
prepareUnits(d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint), lower)
mountUnitList.append(mountUnitName(lower))
# set up one unit, which depends on all mount units, so users can set
# only one dependency in their units to make sure software starts
# when all overlays are mounted
prepareGlobalUnit(mountUnitList)
}
# 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'), ' ' +
d.getVar('systemd_system_unitdir') + '/' + 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}
done
}
addtask create_overlayfs_units before do_install
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