Function blkioTestDevice

integration/container/update_linux_test.go:225–250

blkioTestDevice finds a usable block device on the host by examining the device backing the root filesystem. The returned path (e.g. "/dev/sda") and the decimal major:minor string are suitable for docker update flags and cgroup file lookups respectively.

(t *testing.T)

// and the decimal major:minor string are suitable for docker update flags and
// cgroup file lookups respectively.
func blkioTestDevice(t *testing.T) (devPath, majMin string) {
	t.Helper()

	var st unix.Stat_t
	assert.NilError(t, unix.Stat("/", &st), "stat /")

	major := unix.Major(st.Dev)
	minor := unix.Minor(st.Dev)

	// Resolve the device name via sysfs so we get a real /dev/… path.
	uevent, err := os.ReadFile(fmt.Sprintf("/sys/dev/block/%d:%d/uevent", major, minor))
	if err != nil {
		t.Skipf("cannot resolve block device for / from sysfs: %v", err)
	}
	var name string
	for _, line := range strings.Split(string(uevent), "\n") {
		if after, ok := strings.CutPrefix(line, "DEVNAME="); ok {
			name = strings.TrimSpace(after)
			break
		}
	}
	if name == "" {
		t.Skip("DEVNAME not found in sysfs uevent for / block device")
	}
	return "/dev/" + name, fmt.Sprintf("%d:%d", major, minor)
}

// parseIOMax returns the value of field (rbps/wbps/riops/wiops) for the given
// major:minor device from a cgroup v2 io.max file content.