Hi Bruce,
Thanks for a quick feedback.
Hi Vyacheslav,
This looks like it could be quite useful, but a few comments came to
mind on a really quick scan.
Since this is systemd based, it should probably have
REQUIRED_DISTRO_FEATURES = "systemd", to ensure that the rest of the
system and packages are consistently enabled.
Will include it in my v2.
As part of getting this into core, it needs some sort of test cases /
test suite (and one that covers the different modes you describe in
the class) .. so something like a test image (a user) and the tests
themselves.
Could you please give me a few hints as to where current tests are
stored and how to run them? Is it meta-selftest layer?
It really also needs a maintainer entry, since otherwise the
maintenance work falls to the same already overloaded folks.
You mean just an entry like:
MAINTAINER = "Vyacheslav Yurkov <uvv.m...@gmail.com>
in the class itself?
Because meta/conf/distro/include/maintainers.inc mentions only recipe
maintainers.
Since this is intended to be used on a per-recipe basis (at least that
is my understanding from reading it), what happens if two recipes
create conflicting overlay mounts ? or if the mentioned data.mount is
not present in the image ?
These are good questions. I guess if two recipes would try to use the
same mounts, then do_rootfs should simply fail the same way when two
recipes install the same file.
As for handling a mount.unit, that has to be done on an image level, I
guess. The other question is how to do that.. Perhaps a QA-hook in
ROOTFS_POSTPROCESS_COMMAND, which checks the file existence (not
validity though!)?
Vyacheslav
Bruce
Signed-off-by: Vyacheslav Yurkov <uvv.m...@gmail.com>
---
meta/classes/overlayfs.bbclass | 132 +++++++++++++++++++++++++++++++++
1 file changed, 132 insertions(+)
create mode 100644 meta/classes/overlayfs.bbclass
diff --git a/meta/classes/overlayfs.bbclass b/meta/classes/overlayfs.bbclass
new file mode 100644
index 0000000000..7fac3e696e
--- /dev/null
+++ b/meta/classes/overlayfs.bbclass
@@ -0,0 +1,132 @@
+# 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
+#
+# OVERLAYFS_MOUNT_POINT[data] ?= "/data"
+#
+# The class assumes you have a data.mount systemd unit defined elsewhere in
your
+# BSP 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
+# what to have a writable location on the file system, but not interested
where the data
+# survive a reboot. The 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"
+
+OVERLAYFS_WRITABLE_PATHS[data] ?= ""
+
+inherit systemd
+
+def strForBash(s):
+ return s.replace('\\', '\\\\')
+
+def unitFileList(d):
+ fileList = []
+ overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT")
+ for mountPoint in overlayMountPoints:
+ for path in d.getVarFlag('OVERLAYFS_WRITABLE_PATHS',
mountPoint).split():
+ fileList.append(mountUnitName(path))
+ fileList.append(helperUnitName(path))
+
+ return fileList
+
+# this function is based on
https://github.com/systemd/systemd/blob/main/src/basic/unit-name.c
+def escapeSystemdUnitName(path):
+ escapeMap = {
+ '/': '-',
+ '-': "\\x2d",
+ '\\': "\\x5d"
+ }
+ return "".join([escapeMap.get(c, c) for c in path.strip('/')])
+
+def mountUnitName(unit):
+ return escapeSystemdUnitName(unit) + '.mount'
+
+def helperUnitName(unit):
+ return escapeSystemdUnitName(unit) + '-create-upper-dir.service'
+
+python do_create_overlayfs_units() {
+ CreateDirsUnitTemplate = """[Unit]
+Description=Overlayfs directories setup
+Requires={DATA_MOUNT_UNIT}
+After={DATA_MOUNT_UNIT}
+DefaultDependencies=no
+
+[Service]
+Type=oneshot
+ExecStart=mkdir -p {DATA_MOUNT_POINT}/workdir{LOWERDIR} && mkdir -p
{DATA_MOUNT_POINT}/upper{LOWERDIR}
+RemainAfterExit=true
+StandardOutput=journal
+
+[Install]
+WantedBy=multi-user.target
+"""
+ MountUnitTemplate = """[Unit]
+Description=Overlayfs mount unit
+Requires={CREATE_DIRS_SERVICE}
+After={CREATE_DIRS_SERVICE}
+
+[Mount]
+What=overlay
+Where={LOWERDIR}
+Type=overlay
+Options=lowerdir={LOWERDIR},upperdir={DATA_MOUNT_POINT}/upper{LOWERDIR},workdir={DATA_MOUNT_POINT}/workdir{LOWERDIR}
+
+[Install]
+WantedBy=multi-user.target
+"""
+
+ def prepareUnits(data, lower):
+ args = {
+ 'DATA_MOUNT_POINT': data,
+ '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:
+ f.write(MountUnitTemplate.format(**args))
+
+ with open(os.path.join(d.getVar('WORKDIR'), helperUnitName(lower)),
'w') as f:
+ f.write(CreateDirsUnitTemplate.format(**args))
+
+ 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 () {
+ 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}
+ done
+}
+
+addtask create_overlayfs_units before do_install
--
2.28.0
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