func ensureThinLsKernelVersion()

in container/docker/factory.go [245:303]
39 lines of code
11 McCabe index (conditional complexity)

func ensureThinLsKernelVersion(kernelVersion string) error {
	// kernel 4.4.0 has the proper bug fixes to allow thin_ls to work without corrupting the thin pool
	minKernelVersion := semver.MustParse("4.4.0")
	// RHEL 7 kernel 3.10.0 release >= 366 has the proper bug fixes backported from 4.4.0 to allow
	// thin_ls to work without corrupting the thin pool
	minRhel7KernelVersion := semver.MustParse("3.10.0")

	matches := VersionRe.FindStringSubmatch(kernelVersion)
	if len(matches) < 4 {
		return fmt.Errorf("error parsing kernel version: %q is not a semver", kernelVersion)
	}

	sem, err := semver.Make(matches[0])
	if err != nil {
		return err
	}

	if sem.GTE(minKernelVersion) {
		// kernel 4.4+ - good
		return nil
	}

	// Certain RHEL/Centos 7.x kernels have a backport to fix the corruption bug
	if !strings.Contains(kernelVersion, ".el7") {
		// not a RHEL 7.x kernel - won't work
		return fmt.Errorf("kernel version 4.4.0 or later is required to use thin_ls - you have %q", kernelVersion)
	}

	// RHEL/Centos 7.x from here on
	if sem.Major != 3 {
		// only 3.x kernels *may* work correctly
		return fmt.Errorf("RHEL/Centos 7.x kernel version 3.10.0-366 or later is required to use thin_ls - you have %q", kernelVersion)
	}

	if sem.GT(minRhel7KernelVersion) {
		// 3.10.1+ - good
		return nil
	}

	if sem.EQ(minRhel7KernelVersion) {
		// need to check release
		releaseRE := regexp.MustCompile(`^[^-]+-([0-9]+)\.`)
		releaseMatches := releaseRE.FindStringSubmatch(kernelVersion)
		if len(releaseMatches) != 2 {
			return fmt.Errorf("unable to determine RHEL/Centos 7.x kernel release from %q", kernelVersion)
		}

		release, err := strconv.Atoi(releaseMatches[1])
		if err != nil {
			return fmt.Errorf("error parsing release %q: %v", releaseMatches[1], err)
		}

		if release >= 366 {
			return nil
		}
	}

	return fmt.Errorf("RHEL/Centos 7.x kernel version 3.10.0-366 or later is required to use thin_ls - you have %q", kernelVersion)
}