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Diffstat (limited to 'meta/classes/overlayfs.bbclass')
-rw-r--r-- | meta/classes/overlayfs.bbclass | 111 |
1 files changed, 111 insertions, 0 deletions
diff --git a/meta/classes/overlayfs.bbclass b/meta/classes/overlayfs.bbclass new file mode 100644 index 0000000000..8d9b59c9bf --- /dev/null +++ b/meta/classes/overlayfs.bbclass | |||
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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 | # The class assumes you have a data.mount systemd unit defined in your | ||
20 | # systemd-machine-units recipe and installed to the image. | ||
21 | # | ||
22 | # Then you can specify writable directories on a recipe base | ||
23 | # | ||
24 | # OVERLAYFS_WRITABLE_PATHS[data] = "/usr/share/my-custom-application" | ||
25 | # | ||
26 | # To support several mount points you can use a different variable flag. Assume we | ||
27 | # want to have a writable location on the file system, but not interested where the data | ||
28 | # survive a reboot. Then we could have a mnt-overlay.mount unit for a tmpfs file system: | ||
29 | # | ||
30 | # OVERLAYFS_MOUNT_POINT[mnt-overlay] = "/mnt/overlay" | ||
31 | # OVERLAYFS_WRITABLE_PATHS[mnt-overlay] = "/usr/share/another-application" | ||
32 | # | ||
33 | # Note: the class does not support /etc directory itself, because systemd depends on it | ||
34 | |||
35 | REQUIRED_DISTRO_FEATURES += "systemd overlayfs" | ||
36 | |||
37 | inherit systemd features_check | ||
38 | |||
39 | python do_create_overlayfs_units() { | ||
40 | CreateDirsUnitTemplate = """[Unit] | ||
41 | Description=Overlayfs directories setup | ||
42 | Requires={DATA_MOUNT_UNIT} | ||
43 | After={DATA_MOUNT_UNIT} | ||
44 | DefaultDependencies=no | ||
45 | |||
46 | [Service] | ||
47 | Type=oneshot | ||
48 | ExecStart=mkdir -p {DATA_MOUNT_POINT}/workdir{LOWERDIR} && mkdir -p {DATA_MOUNT_POINT}/upper{LOWERDIR} | ||
49 | RemainAfterExit=true | ||
50 | StandardOutput=journal | ||
51 | |||
52 | [Install] | ||
53 | WantedBy=multi-user.target | ||
54 | """ | ||
55 | MountUnitTemplate = """[Unit] | ||
56 | Description=Overlayfs mount unit | ||
57 | Requires={CREATE_DIRS_SERVICE} | ||
58 | After={CREATE_DIRS_SERVICE} | ||
59 | |||
60 | [Mount] | ||
61 | What=overlay | ||
62 | Where={LOWERDIR} | ||
63 | Type=overlay | ||
64 | Options=lowerdir={LOWERDIR},upperdir={DATA_MOUNT_POINT}/upper{LOWERDIR},workdir={DATA_MOUNT_POINT}/workdir{LOWERDIR} | ||
65 | |||
66 | [Install] | ||
67 | WantedBy=multi-user.target | ||
68 | """ | ||
69 | |||
70 | def prepareUnits(data, lower): | ||
71 | from oe.overlayfs import mountUnitName, helperUnitName | ||
72 | |||
73 | args = { | ||
74 | 'DATA_MOUNT_POINT': data, | ||
75 | 'DATA_MOUNT_UNIT': mountUnitName(data), | ||
76 | 'CREATE_DIRS_SERVICE': helperUnitName(lower), | ||
77 | 'LOWERDIR': lower, | ||
78 | } | ||
79 | |||
80 | with open(os.path.join(d.getVar('WORKDIR'), mountUnitName(lower)), 'w') as f: | ||
81 | f.write(MountUnitTemplate.format(**args)) | ||
82 | |||
83 | with open(os.path.join(d.getVar('WORKDIR'), helperUnitName(lower)), 'w') as f: | ||
84 | f.write(CreateDirsUnitTemplate.format(**args)) | ||
85 | |||
86 | overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT") | ||
87 | for mountPoint in overlayMountPoints: | ||
88 | for lower in d.getVarFlag('OVERLAYFS_WRITABLE_PATHS', mountPoint).split(): | ||
89 | prepareUnits(d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint), lower) | ||
90 | } | ||
91 | |||
92 | # we need to generate file names early during parsing stage | ||
93 | python () { | ||
94 | from oe.overlayfs import strForBash, unitFileList | ||
95 | |||
96 | unitList = unitFileList(d) | ||
97 | for unit in unitList: | ||
98 | d.appendVar('SYSTEMD_SERVICE:' + d.getVar('PN'), ' ' + unit); | ||
99 | d.appendVar('FILES:' + d.getVar('PN'), ' ' + strForBash(unit)) | ||
100 | |||
101 | d.setVar('OVERLAYFS_UNIT_LIST', ' '.join([strForBash(s) for s in unitList])) | ||
102 | } | ||
103 | |||
104 | do_install:append() { | ||
105 | install -d ${D}${systemd_system_unitdir} | ||
106 | for unit in ${OVERLAYFS_UNIT_LIST}; do | ||
107 | install -m 0444 ${WORKDIR}/${unit} ${D}${systemd_system_unitdir} | ||
108 | done | ||
109 | } | ||
110 | |||
111 | addtask create_overlayfs_units before do_install | ||