Only fetch network stats we use.

The dynamic version using WalkPath() was expensive and we only used some
of the stats anyways.

Signed-off-by: Victor Marmol <vmarmol@google.com>

network/stats.go

@@ -2,7 +2,6 @@ package network
 
 import (
 	"io/ioutil"
-	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -25,45 +24,51 @@ func GetStats(networkState *NetworkState) (*NetworkStats, error) {
 	if networkState.VethHost == "" {
 		return &NetworkStats{}, nil
 	}
-	data, err := readSysfsNetworkStats(networkState.VethHost)
-	if err != nil {
-		return nil, err
+
+	out := &NetworkStats{}
+
+	type netStatsPair struct {
+		// Where to write the output.
+		Out *uint64
+
+		// The network stats file to read.
+		File string
 	}
 
 	// Ingress for host veth is from the container. Hence tx_bytes stat on the host veth is actually number of bytes received by the container.
-	return &NetworkStats{
-		RxBytes:   data["tx_bytes"],
-		RxPackets: data["tx_packets"],
-		RxErrors:  data["tx_errors"],
-		RxDropped: data["tx_dropped"],
-		TxBytes:   data["rx_bytes"],
-		TxPackets: data["rx_packets"],
-		TxErrors:  data["rx_errors"],
-		TxDropped: data["rx_dropped"],
-	}, nil
+	netStats := []netStatsPair{
+		{Out: &out.RxBytes, File: "tx_bytes"},
+		{Out: &out.RxPackets, File: "tx_packets"},
+		{Out: &out.RxErrors, File: "tx_errors"},
+		{Out: &out.RxDropped, File: "tx_dropped"},
+
+		{Out: &out.TxBytes, File: "rx_bytes"},
+		{Out: &out.TxPackets, File: "rx_packets"},
+		{Out: &out.TxErrors, File: "rx_errors"},
+		{Out: &out.TxDropped, File: "rx_dropped"},
+	}
+	for _, netStat := range netStats {
+		data, err := readSysfsNetworkStats(networkState.VethHost, netStat.File)
+		if err != nil {
+			return nil, err
+		}
+		*(netStat.Out) = data
+	}
+
+	return out, nil
 }
 
-// Reads all the statistics available under /sys/class/net/<EthInterface>/statistics as a map with file name as key and data as integers.
-func readSysfsNetworkStats(ethInterface string) (map[string]uint64, error) {
-	out := make(map[string]uint64)
-
-	fullPath := filepath.Join("/sys/class/net", ethInterface, "statistics/")
-	err := filepath.Walk(fullPath, func(path string, _ os.FileInfo, _ error) error {
-		// skip fullPath.
-		if path == fullPath {
-			return nil
-		}
-		base := filepath.Base(path)
-		data, err := ioutil.ReadFile(path)
+// Reads the specified statistics available under /sys/class/net/<EthInterface>/statistics
+func readSysfsNetworkStats(ethInterface, statsFile string) (uint64, error) {
+	fullPath := filepath.Join("/sys/class/net", ethInterface, "statistics", statsFile)
+	data, err := ioutil.ReadFile(fullPath)
 	if err != nil {
-			return err
+		return 0, err
 	}
 	value, err := strconv.ParseUint(strings.TrimSpace(string(data)), 10, 64)
 	if err != nil {
-			return err
+		return 0, err
 	}
-		out[base] = value
-		return nil
-	})
-	return out, err
+
+	return value, err
 }