1# Class for generation of overlayfs mount units 2# 3# It's often desired in Embedded System design to have a read-only rootfs. 4# But a lot of different applications might want to have a read-write access to 5# some parts of a filesystem. It can be especially useful when your update mechanism 6# overwrites the whole rootfs, but you want your application data to be preserved 7# between updates. This class provides a way to achieve that by means 8# of overlayfs and at the same time keeping the base rootfs read-only. 9# 10# Usage example. 11# 12# Set a mount point for a partition overlayfs is going to use as upper layer 13# in your machine configuration. Underlying file system can be anything that 14# is supported by overlayfs. This has to be done in your machine configuration. 15# QA check fails to catch file existence if you redefine this variable in your recipe! 16# 17# OVERLAYFS_MOUNT_POINT[data] ?= "/data" 18# 19# Per default the class assumes you have a corresponding fstab entry or systemd 20# mount unit (data.mount in this case) for this mount point installed on the 21# image, for instance via a wks script or the systemd-machine-units recipe. 22# 23# If the mount point is handled somewhere else, e.g. custom boot or preinit 24# scripts or in a initramfs, then this QA check can be skipped by adding 25# mount-configured to the related OVERLAYFS_QA_SKIP flag: 26# 27# OVERLAYFS_QA_SKIP[data] = "mount-configured" 28# 29# To use the overlayfs, you just have to specify writable directories inside 30# their recipe: 31# 32# OVERLAYFS_WRITABLE_PATHS[data] = "/usr/share/my-custom-application" 33# 34# To support several mount points you can use a different variable flag. Assume we 35# want to have a writable location on the file system, but not interested where the data 36# survive a reboot. Then we could have a mnt-overlay.mount unit for a tmpfs file system: 37# 38# OVERLAYFS_MOUNT_POINT[mnt-overlay] = "/mnt/overlay" 39# OVERLAYFS_WRITABLE_PATHS[mnt-overlay] = "/usr/share/another-application" 40# 41# If your recipe deploys a systemd service, then it should require and be 42# started after the ${PN}-overlays.service to make sure that all overlays are 43# mounted beforehand. 44# 45# Note: the class does not support /etc directory itself, because systemd depends on it 46# For /etc directory use overlayfs-etc class 47 48REQUIRED_DISTRO_FEATURES += "systemd overlayfs" 49 50inherit systemd features_check 51 52OVERLAYFS_CREATE_DIRS_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-create-dirs.service.in" 53OVERLAYFS_MOUNT_UNIT_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-unit.mount.in" 54OVERLAYFS_ALL_OVERLAYS_TEMPLATE ??= "${COREBASE}/meta/files/overlayfs-all-overlays.service.in" 55 56python do_create_overlayfs_units() { 57 from oe.overlayfs import mountUnitName 58 59 with open(d.getVar("OVERLAYFS_CREATE_DIRS_TEMPLATE"), "r") as f: 60 CreateDirsUnitTemplate = f.read() 61 with open(d.getVar("OVERLAYFS_MOUNT_UNIT_TEMPLATE"), "r") as f: 62 MountUnitTemplate = f.read() 63 with open(d.getVar("OVERLAYFS_ALL_OVERLAYS_TEMPLATE"), "r") as f: 64 AllOverlaysTemplate = f.read() 65 66 def prepareUnits(data, lower): 67 from oe.overlayfs import helperUnitName 68 69 args = { 70 'DATA_MOUNT_POINT': data, 71 'DATA_MOUNT_UNIT': mountUnitName(data), 72 'CREATE_DIRS_SERVICE': helperUnitName(lower), 73 'LOWERDIR': lower, 74 } 75 76 bb.debug(1, "Generate systemd unit %s" % mountUnitName(lower)) 77 with open(os.path.join(d.getVar('WORKDIR'), mountUnitName(lower)), 'w') as f: 78 f.write(MountUnitTemplate.format(**args)) 79 80 bb.debug(1, "Generate helper systemd unit %s" % helperUnitName(lower)) 81 with open(os.path.join(d.getVar('WORKDIR'), helperUnitName(lower)), 'w') as f: 82 f.write(CreateDirsUnitTemplate.format(**args)) 83 84 def prepareGlobalUnit(dependentUnits): 85 from oe.overlayfs import allOverlaysUnitName 86 args = { 87 'ALL_OVERLAYFS_UNITS': " ".join(dependentUnits), 88 'PN': d.getVar('PN') 89 } 90 91 bb.debug(1, "Generate systemd unit with all overlays %s" % allOverlaysUnitName(d)) 92 with open(os.path.join(d.getVar('WORKDIR'), allOverlaysUnitName(d)), 'w') as f: 93 f.write(AllOverlaysTemplate.format(**args)) 94 95 mountUnitList = [] 96 overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT") 97 for mountPoint in overlayMountPoints: 98 bb.debug(1, "Process variable flag %s" % mountPoint) 99 lowerList = d.getVarFlag('OVERLAYFS_WRITABLE_PATHS', mountPoint) 100 if not lowerList: 101 bb.note("No mount points defined for %s flag, skipping" % (mountPoint)) 102 continue 103 for lower in lowerList.split(): 104 bb.debug(1, "Prepare mount unit for %s with data mount point %s" % 105 (lower, d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint))) 106 prepareUnits(d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint), lower) 107 mountUnitList.append(mountUnitName(lower)) 108 109 # set up one unit, which depends on all mount units, so users can set 110 # only one dependency in their units to make sure software starts 111 # when all overlays are mounted 112 prepareGlobalUnit(mountUnitList) 113} 114 115# we need to generate file names early during parsing stage 116python () { 117 from oe.overlayfs import strForBash, unitFileList 118 119 unitList = unitFileList(d) 120 for unit in unitList: 121 d.appendVar('SYSTEMD_SERVICE:' + d.getVar('PN'), ' ' + unit) 122 d.appendVar('FILES:' + d.getVar('PN'), ' ' + 123 d.getVar('systemd_system_unitdir') + '/' + strForBash(unit)) 124 125 d.setVar('OVERLAYFS_UNIT_LIST', ' '.join([strForBash(s) for s in unitList])) 126} 127 128do_install:append() { 129 install -d ${D}${systemd_system_unitdir} 130 for unit in ${OVERLAYFS_UNIT_LIST}; do 131 install -m 0444 ${WORKDIR}/${unit} ${D}${systemd_system_unitdir} 132 done 133} 134 135addtask create_overlayfs_units before do_install 136