utils: Move FC's function to revert bytes to utils

Firecracker's revertBytes function, now called "RevertBytes", can be
exposed as part of the virtcontainers' utils file, as this function will
be reused by Cloud Hypervisor, when adding the rate limiter logic there.

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

src/runtime/virtcontainers/fc.go

@@ -938,7 +938,7 @@ func (fc *firecracker) fcAddNetDevice(ctx context.Context, endpoint Endpoint) {
 
 		// kata-defined rxSize is in bits with scaling factors of 1000, but firecracker-defined
 		// rxSize is in bytes with scaling factors of 1024, need reversion.
-		rxSize = revertBytes(rxSize / 8)
+		rxSize = utils.RevertBytes(rxSize / 8)
 		rxTokenBucket := models.TokenBucket{
 			RefillTime: &refillTime,
 			Size:       &rxSize,
@@ -955,7 +955,7 @@ func (fc *firecracker) fcAddNetDevice(ctx context.Context, endpoint Endpoint) {
 
 		// kata-defined txSize is in bits with scaling factors of 1000, but firecracker-defined
 		// txSize is in bytes with scaling factors of 1024, need reversion.
-		txSize = revertBytes(txSize / 8)
+		txSize = utils.RevertBytes(txSize / 8)
 		txTokenBucket := models.TokenBucket{
 			RefillTime: &refillTime,
 			Size:       &txSize,
@@ -1266,15 +1266,3 @@ func (fc *firecracker) GenerateSocket(id string) (interface{}, error) {
 func (fc *firecracker) IsRateLimiterBuiltin() bool {
 	return true
 }
-
-// In firecracker, it accepts the size of rate limiter in scaling factors of 2^10(1024)
-// But in kata-defined rate limiter, for better Human-readability, we prefer scaling factors of 10^3(1000).
-// func revertByte reverts num from scaling factors of 1000 to 1024, e.g. 10000000(10MB) to 10485760.
-func revertBytes(num uint64) uint64 {
-	a := num / 1000
-	b := num % 1000
-	if a == 0 {
-		return num
-	}
-	return 1024*revertBytes(a) + b
-}

src/runtime/virtcontainers/fc_test.go

@@ -50,17 +50,6 @@ func TestFCTruncateID(t *testing.T) {
 	assert.Equal(expectedID, id)
 }
 
-func TestRevertBytes(t *testing.T) {
-	assert := assert.New(t)
-
-	//10MB
-	testNum := uint64(10000000)
-	expectedNum := uint64(10485760)
-
-	num := revertBytes(testNum)
-	assert.Equal(expectedNum, num)
-}
-
 func TestFCParseVersion(t *testing.T) {
 	assert := assert.New(t)
 

src/runtime/virtcontainers/utils/utils.go

@@ -458,3 +458,19 @@ func getAllParentPaths(path string) []string {
 	// remove the "/" or "." from the return result
 	return paths[1:]
 }
+
+// In Cloud Hypervisor, as well as in Firecracker, the crate used by the VMMs
+// accepts the size of rate limiter in scaling factors of 2^10(1024).
+// But in kata-defined rate limiter, for better Human-readability, we prefer
+// scaling factors of 10^3(1000).
+//
+// func revertBytes reverts num from scaling factors of 1000 to 1024, e.g.
+// 10000000(10MB) to 10485760.
+func RevertBytes(num uint64) uint64 {
+	a := num / 1000
+	b := num % 1000
+	if a == 0 {
+		return num
+	}
+	return 1024*RevertBytes(a) + b
+}

src/runtime/virtcontainers/utils/utils_test.go

@@ -569,3 +569,14 @@ func TestGetAllParentPaths(t *testing.T) {
 		assert.Equal(tc.parents, getAllParentPaths(tc.targetPath))
 	}
 }
+
+func TestRevertBytes(t *testing.T) {
+	assert := assert.New(t)
+
+	//10MB
+	testNum := uint64(10000000)
+	expectedNum := uint64(10485760)
+
+	num := RevertBytes(testNum)
+	assert.Equal(expectedNum, num)
+}