core: refactor clock handling

core/clock.go

@@ -1,3 +1,20 @@
+// Package core provides timing and clock functionality for traffic control operations.
+//
+// IMPORTANT: Before using any timing functions (Duration2TcTime, Time2Tick, etc.),
+// you must initialize the clock parameters by calling InitializeClock().
+//
+// Example usage:
+//   import "github.com/florianl/go-tc/core"
+//
+//   func main() {
+//       if err := core.InitializeClock(); err != nil {
+//           log.Printf("Warning: failed to initialize clock: %v", err)
+//       }
+//
+//       // Now you can use timing functions
+//       ticks := core.Time2Tick(1000)
+//   }
+
 package core
 
 import (
@@ -8,13 +25,49 @@ import (
 var (
 	tickInUSec  float64
 	clockFactor float64
+
+	// isSet indicates whether the clock parameters have been initialized.
+	isSet bool
 )
 
 const (
 	// iproute2/include/utils.h:timeUnitsPerSec
 	timeUnitsPerSec = 1000000
 )
 
+// InitializeClock initializes the clock parameters by reading from /proc/net/psched on Linux.
+// On non-Linux platforms, it sets default values (1.0 for both parameters).
+// This function must be called before using any of the timing functions.
+// It returns an error if the clock parameters cannot be read on Linux.
+func InitializeClock() error {
+	isSet = true
+	return initializeClock()
+}
+
+// SetClockParameters allows manual configuration of the clock parameters.
+// This is useful for testing or when custom clock values are needed.
+// clockFactor is the clock resolution factor, tickInUSec is the tick to microsecond conversion factor.
+func SetClockParameters(newClockFactor, newTickInUSec float64) {
+	isSet = true
+	clockFactor = newClockFactor
+	tickInUSec = newTickInUSec
+}
+
+// IsClockInitialized returns true if the clock parameters have been initialized.
+func IsClockInitialized() bool {
+	return isSet
+}
+
+// GetClockFactor returns the current clock factor value.
+func GetClockFactor() float64 {
+	return clockFactor
+}
+
+// GetTickInUSec returns the current tick in microseconds conversion factor.
+func GetTickInUSec() float64 {
+	return tickInUSec
+}
+
 // Duration2TcTime implements iproute2/tc/q_netem.c:get_ticks().
 // It converts a given duration into a time value that can be converted to ticks with Time2Tick().
 // On error it returns syscall.EINVAL.

core/clock_linux.go

@@ -8,12 +8,11 @@ import (
 	"os"
 )
 
-func init() {
+// initializeClock reads clock parameters from /proc/net/psched and initializes the global variables.
+func initializeClock() error {
 	var err error
 	clockFactor, tickInUSec, err = readPsched()
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "%s", err)
-	}
+	return err
 }
 
 func readPsched() (float64, float64, error) {

core/clock_other.go

@@ -3,7 +3,9 @@
 
 package core
 
-func init() {
+// initializeClock sets default clock parameters for non-Linux platforms.
+func initializeClock() error {
 	clockFactor = 1.0
 	tickInUSec = 1.0
+	return nil
 }

core/clock_test.go

@@ -2,12 +2,20 @@ package core
 
 import (
 	"errors"
+	"fmt"
 	"syscall"
 	"testing"
 	"time"
 )
 
 func TestClock(t *testing.T) {
+	// Initialize clock for testing
+	if err := InitializeClock(); err != nil {
+		t.Logf("Warning: failed to initialize clock: %v", err)
+		// Set fallback values for testing
+		SetClockParameters(1.0, 1.0)
+	}
+
 	t.Run("Tick", func(t *testing.T) {
 		tick := Time2Tick(0xC0FFEE)
 		time := Tick2Time(tick)
@@ -70,3 +78,29 @@ func TestDuration2TcTime(t *testing.T) {
 		})
 	}
 }
+
+// ExampleInitializeClock demonstrates the clock initialization API
+func ExampleInitializeClock() {
+	// Initialize clock parameters
+	if err := InitializeClock(); err != nil {
+		fmt.Printf("Warning: failed to initialize clock: %v\n", err)
+		// You can optionally set fallback values if initialization fails
+		SetClockParameters(1.0, 1.0)
+	}
+
+	// Set known values for predictable output
+	SetClockParameters(1.0, 1.0)
+
+	// Now you can use timing functions
+	ticks := Time2Tick(1000)
+	fmt.Printf("Time2Tick(1000) = %d\n", ticks)
+
+	// You can also get the current clock parameters
+	clockFactor := GetClockFactor()
+	tickInUSec := GetTickInUSec()
+	fmt.Printf("Clock Factor: %.1f, Tick in µs: %.1f\n", clockFactor, tickInUSec)
+
+	// Output:
+	// Time2Tick(1000) = 1000
+	// Clock Factor: 1.0, Tick in µs: 1.0
+}

example_netem_test.go

@@ -95,6 +95,12 @@ func ExampleNetem() {
 }
 
 func ExampleNetem_with_delay() {
+	// Initialize clock parameters
+	if err := core.InitializeClock(); err != nil {
+		fmt.Fprintf(os.Stderr, "could not initialize clock: %v\n", err)
+		return
+	}
+
 	tcIface := "ExampleNetemDelay"
 
 	rtnl, err := setupDummyInterface(tcIface)

q_netem_test.go

@@ -10,6 +10,13 @@ import (
 )
 
 func TestNetem(t *testing.T) {
+	// Initialize clock parameters for timing functions
+	if err := core.InitializeClock(); err != nil {
+		t.Logf("Warning: failed to initialize clock: %v", err)
+		// Set fallback values for testing
+		core.SetClockParameters(1.0, 1.0)
+	}
+
 	delayDist := []int16{9, 7, 5, 3, 1}
 	tests := map[string]struct {
 		val  Netem

q_tbf_test.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"testing"
 
+	"github.com/florianl/go-tc/core"
 	"github.com/google/go-cmp/cmp"
 )
 
@@ -30,6 +31,13 @@ func TestTbf(t *testing.T) {
 		}}},
 	}
 
+	// Initialize clock parameters for timing functions
+	if err := core.InitializeClock(); err != nil {
+		t.Logf("Warning: failed to initialize clock: %v", err)
+		// Set fallback values for testing
+		core.SetClockParameters(1.0, 1.0)
+	}
+
 	for name, testcase := range tests {
 		t.Run(name, func(t *testing.T) {
 			data, err1 := marshalTbf(&testcase.val)

ratetable.go

@@ -11,6 +11,10 @@ import (
 
 // iproute2/tc/tc_core.c:tc_calc_rtable()
 func generateRateTable(pol *Policy) ([]byte, error) {
+	if !core.IsClockInitialized() {
+		return nil, fmt.Errorf("generateRateTable: use " +
+			"github.com/florianl/go-tc/core.InitializeClock() first")
+	}
 	var rate [256]uint32
 
 	if pol == nil {

ratetable_linux_test.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"testing"
 
+	"github.com/florianl/go-tc/core"
 	"github.com/florianl/go-tc/internal/unix"
 )
 
@@ -184,6 +185,12 @@ func TestGenerateRateTable(t *testing.T) {
 			expect: rate8kbitBurst5kbPeakrate12kbitMpu64Mtu1464Drop,
 		},
 	}
+	// Initialize clock parameters for timing functions
+	if err := core.InitializeClock(); err != nil {
+		t.Logf("Warning: failed to initialize clock: %v", err)
+		// Set fallback values for testing
+		core.SetClockParameters(1.0, 1.0)
+	}
 
 	for name, testcase := range tests {
 		t.Run(name, func(t *testing.T) {