support flag file to runtime switch to cgroupv1 #35
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Pass a custom init commands (init.wrapper) to 'systemctl switch-root' when leaving the initramfs. This init.wrapper is responsible for disabling all cgroup controllers and unmounting cgroup2, and injecting (by means of a bind mount) custom kernel arguments so that sysroot systemd sets up cgroupv1. We're adding this so that Flatcar users don't have to reboot to switch back to cgroupv1, which is disruptive in many deployments. The usage of init.wrapper is conditional on two things: * initramfs used up cgroupv2. * user opted into to this behavior by creating the `/etc/flatcar-cgroupv1` flag file There is a reason to not go through init.wrapper unconditionally, and decide whether to take action-or-not there. When systemd runs in sysroot and initramfs, it serializes some data structures and passes them from the initramfs to allow some introspection. I believe this is primarily systemd-analyze timing information. This doesn't work when we inject a custom init between sysroot and initramfs (init.wrapper), so ensure we only use the custom init when we really need to. This is accomplished by passing the init.wrapper path through an INIT environment variable, which is only defined when '/etc/flatcar-cgroupv1' exists in the sysroot. An alternative would have been to conditionally symlink the override snippet, which would get applied in the 'systemctl daemon-reload' in 'initrd-parse-etc.service'. Neither option is particularly obvious, but this one seems slightly easier to follow.
…fault Moving controllers between cgroup v1 and v2 is difficult once they have been used. So create a system.conf.d snippet that sets the Default*Accounting=no so that moving controllers becomes possible.
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…ange This pulls in flatcar/bootengine#35 and flatcar/init#62, which enable boot time switching back to legacy cgroups by creating a flag files (/etc/flatcar-cgroupv1) from ignition.
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…ange This pulls in flatcar/bootengine#35 and flatcar/init#62, which enable boot time switching back to legacy cgroups by creating a flag files (/etc/flatcar-cgroupv1) from ignition.
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…ange This pulls in flatcar/bootengine#35 and flatcar/init#62, which enable boot time switching back to legacy cgroups by creating a flag files (/etc/flatcar-cgroupv1) from ignition.
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support flag file to runtime switch to cgroupv1
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…ange This pulls in flatcar/bootengine#35 and flatcar/init#62, which enable boot time switching back to legacy cgroups by creating a flag files (/etc/flatcar-cgroupv1) from ignition. Also contains the subsequent bugfix to coreos-init: c21ee83 "coreos-base/coreos-init: move processes to root cgroup before unbinding controllers"
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…ange This pulls in flatcar/bootengine#35 and flatcar/init#62, which enable boot time switching back to legacy cgroups by creating a flag files (/etc/flatcar-cgroupv1) from ignition. Also contains the subsequent bugfix to coreos-init: c21ee83df0a2302c0b7cfa375a5f191c14800ec8 "coreos-base/coreos-init: move processes to root cgroup before unbinding controllers"
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support flag file to runtime switch to cgroupv1
The idea is to detect the presence of a flag file (
/etc/flatcar-cgroupv1), to callsystemctl switch-rootwithinit.wrapperas an argument.init.wrappertakes care of unmounting the currently mounted cgroup after initramfs, allowing sysroot systemd to remount cgroupv1.The detection is done at the end of initrd-parse-etc.service, and the parameters are passed to initrd-switch-root.service through a temporary environment file.
How to use
To be used with flatcar/init#62.
Testing done
changelog/directory (user-facing change, bug fix, security fix, update)