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Diffstat (limited to 'meta/classes-recipe/overlayfs.bbclass')
| -rw-r--r-- | meta/classes-recipe/overlayfs.bbclass | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/meta/classes-recipe/overlayfs.bbclass b/meta/classes-recipe/overlayfs.bbclass new file mode 100644 index 0000000000..a82763ec10 --- /dev/null +++ b/meta/classes-recipe/overlayfs.bbclass @@ -0,0 +1,142 @@ +# +# 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) + lowerList = d.getVarFlag('OVERLAYFS_WRITABLE_PATHS', mountPoint) + if not lowerList: + bb.note("No mount points defined for %s flag, skipping" % (mountPoint)) + continue + for lower in lowerList.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 +} + +do_create_overlayfs_units[vardeps] += "OVERLAYFS_WRITABLE_PATHS" +addtask create_overlayfs_units before do_install |