Add kernel conntrack counters (#3434)

client/internal/netflow/conntrack/sysctl.go

@@ -0,0 +1,73 @@
+//go:build linux && !android
+
+package conntrack
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	// conntrackAcctPath is the sysctl path for conntrack accounting
+	conntrackAcctPath = "net.netfilter.nf_conntrack_acct"
+)
+
+// EnableAccounting ensures that connection tracking accounting is enabled  in the kernel.
+func (c *ConnTrack) EnableAccounting() {
+	// haven't restored yet
+	if c.sysctlModified {
+		return
+	}
+
+	modified, err := setSysctl(conntrackAcctPath, 1)
+	if err != nil {
+		log.Warnf("Failed to enable conntrack accounting: %v", err)
+		return
+	}
+	c.sysctlModified = modified
+}
+
+// RestoreAccounting restores the connection tracking accounting setting to its original value.
+func (c *ConnTrack) RestoreAccounting() {
+	if !c.sysctlModified {
+		return
+	}
+
+	if _, err := setSysctl(conntrackAcctPath, 0); err != nil {
+		log.Warnf("Failed to restore conntrack accounting: %v", err)
+		return
+	}
+
+	c.sysctlModified = false
+}
+
+// setSysctl sets a sysctl configuration and returns whether it was modified.
+func setSysctl(key string, desiredValue int) (bool, error) {
+	path := fmt.Sprintf("/proc/sys/%s", strings.ReplaceAll(key, ".", "/"))
+
+	currentValue, err := os.ReadFile(path)
+	if err != nil {
+		return false, fmt.Errorf("read sysctl %s: %w", key, err)
+	}
+
+	currentV, err := strconv.Atoi(strings.TrimSpace(string(currentValue)))
+	if err != nil && len(currentValue) > 0 {
+		return false, fmt.Errorf("convert current value to int: %w", err)
+	}
+
+	if currentV == desiredValue {
+		return false, nil
+	}
+
+	// nolint:gosec
+	if err := os.WriteFile(path, []byte(strconv.Itoa(desiredValue)), 0644); err != nil {
+		return false, fmt.Errorf("write sysctl %s: %w", key, err)
+	}
+
+	log.Debugf("Set sysctl %s from %d to %d", key, currentV, desiredValue)
+	return true, nil
+}