fix(agent): use nvethernet MAC counters (#2090)

Co-authored-by: hank <hank@henrygd.me>

agent/network_counters_linux.go

@@ -0,0 +1,71 @@
+//go:build linux
+
+package agent
+
+import (
+	"log/slog"
+	"math"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/safchain/ethtool"
+	psutilNet "github.com/shirou/gopsutil/v4/net"
+)
+
+// correctNvethernetCounters replaces the inflated sysfs byte counters of an
+// nvethernet NIC with its MAC octet counters.
+func correctNvethernetCounters(v *psutilNet.IOCountersStat) {
+	tx, rx, ok := readEthtoolMACOctets(v.Name)
+	if !ok {
+		return
+	}
+	v.BytesSent = tx
+	v.BytesRecv = rx
+}
+
+func isNvidiaEthernet(name string) bool {
+	if name == "" || strings.Contains(name, "/") {
+		return false
+	}
+
+	driverPath := filepath.Join("/sys/class/net", name, "device/driver")
+	target, err := os.Readlink(driverPath)
+	if err != nil {
+		return false
+	}
+	return filepath.Base(target) == "nvethernet"
+}
+
+func readEthtoolMACOctets(name string) (tx, rx uint64, ok bool) {
+	stats, err := ethtool.Stats(name)
+	if err != nil {
+		slog.Debug("Failed to read ethtool network counters", "interface", name, "err", err)
+		return 0, 0, false
+	}
+
+	tx, okTx := ethtoolCounter(stats, "mmc_tx_octetcount_gb", "mmc_tx_octetcount_gb_h")
+	rx, okRx := ethtoolCounter(stats, "mmc_rx_octetcount_gb", "mmc_rx_octetcount_gb_h")
+	if !okTx || !okRx {
+		return 0, 0, false
+	}
+	return tx, rx, true
+}
+
+// ethtoolCounter combines nvethernet's split MMC counters. The driver accumulates
+// the low and high registers into independent 64-bit fields, so the low value can
+// exceed 32 bits and must be added rather than OR'd into the shifted high word.
+func ethtoolCounter(stats map[string]uint64, lowKey, highKey string) (uint64, bool) {
+	low, ok := stats[lowKey]
+	if !ok {
+		return 0, false
+	}
+	high, hasHigh := stats[highKey]
+	if !hasHigh {
+		return low, true
+	}
+	if high > (math.MaxUint64-low)>>32 {
+		return 0, false
+	}
+	return high<<32 + low, true
+}