func createAndAssignCgroups()

in main/vmWatch.go [418:487]
53 lines of code
7 McCabe index (conditional complexity)

func createAndAssignCgroups(lg *slog.Logger, vmwatchSettings *vmWatchSettings, vmWatchPid int) error {
	// get our process and use this to determine the appropriate mount points for the cgroups
	myPid := os.Getpid()
	memoryLimitInBytes := int64(vmwatchSettings.MemoryLimitInBytes)

	telemetry.SendEvent(telemetry.InfoEvent, telemetry.StartVMWatchTask, "Assigning VMWatch process to cgroup")

	// check cgroups mode
	if cgroups.Mode() == cgroups.Unified {
		telemetry.SendEvent(telemetry.InfoEvent, telemetry.StartVMWatchTask, "cgroups v2 detected")
		// in cgroup v2, we need to set the period and quota relative to one another.
		// Quota is the number of microseconds in the period that process can run
		// Period is the length of the period in microseconds
		period := uint64(CGroupV2PeriodMs)
		cpuQuota := int64(vmwatchSettings.MaxCpuPercentage * 10000)
		resources := cgroup2.Resources{
			CPU: &cgroup2.CPU{
				Max: cgroup2.NewCPUMax(&cpuQuota, &period),
			},
			Memory: &cgroup2.Memory{
				Max: &memoryLimitInBytes,
			},
		}

		// in cgroup v2, it appears that a process already in a cgroup can't create a sub group that limits the same
		// kind of resources so we have to do it at the root level.  Reference https://manpath.be/f35/7/cgroups#L557
		manager, err := cgroup2.NewManager("/sys/fs/cgroup", "/vmwatch.slice", &resources)
		if err != nil {
			return err
		}
		err = manager.AddProc(uint64(vmWatchPid))
		if err != nil {
			return err
		}
	} else {
		telemetry.SendEvent(telemetry.InfoEvent, telemetry.StartVMWatchTask, "cgroups v1 detected")
		p := cgroup1.PidPath(myPid)

		cpuPath, err := p("cpu")
		if err != nil {
			return err
		}

		// in cgroup v1, the interval is implied, 1000 == 1 %
		cpuQuota := int64(vmwatchSettings.MaxCpuPercentage * 1000)
		memoryLimitInBytes := int64(vmwatchSettings.MemoryLimitInBytes)

		s := specs.LinuxResources{
			CPU: &specs.LinuxCPU{
				Quota: &cpuQuota,
			},
			Memory: &specs.LinuxMemory{
				Limit: &memoryLimitInBytes,
			},
		}

		control, err := cgroup1.New(cgroup1.StaticPath(cpuPath+"/vmwatch.slice"), &s)
		if err != nil {
			return err
		}
		err = control.AddProc(uint64(vmWatchPid))
		if err != nil {
			return err
		}

		defer control.Delete()
	}

	return nil
}