func guessContainerCgroupPath()

in metric/system/cgroup/util.go [306:356]
40 lines of code
11 McCabe index (conditional complexity)

func guessContainerCgroupPath(v2Loc string, OurPid int) (string, error) {
	// check the cache first
	if cachePath := cgroupContainerPath.get(); cachePath != "" {
		// check the validity of the cache
		rawFile, err := os.ReadFile(filepath.Join(v2Loc, cachePath, "cgroup.procs"))
		// if we get a read error, assume the cache is invalid, move on
		if err == nil {
			if foundMatchingPidInProcsFile(OurPid, string(rawFile)) {
				return cachePath, nil
			}
		}
	}
	// pattern:
	// if in a private cgroup namespace,
	// traverse over the root cgroup path, look for *.procs files
	// go through all of the *.procs files until we have one that contains our pid
	// that path is our cgroup

	foundCgroupPath := ""
	err := filepath.WalkDir(v2Loc, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		if strings.Contains(d.Name(), "procs") {
			pidfile, err := os.ReadFile(path) //nolint: nilerr // we can get lots of weird permissions errors here, so don't fail on an error
			if err != nil {
				return nil //nolint: nilerr // we can get lots of weird permissions errors here, so don't fail on an error
			}
			if foundMatchingPidInProcsFile(OurPid, string(pidfile)) {
				foundCgroupPath = path
				return nil
			}
		}
		return nil
	})
	if err != nil {
		return "", fmt.Errorf("error traversing paths to find cgroup: %w", err)
	}

	if foundCgroupPath == "" {
		return "", nil
	}
	// strip to cgroup path
	cgroupDir := filepath.Dir(foundCgroupPath)
	relativePath := strings.TrimPrefix(cgroupDir, v2Loc)
	cgroupContainerPath.set(relativePath)
	return relativePath, nil
}