fix: redundant zfs pool tag (#10871)

plugins/inputs/zfs/zfs_linux.go

@@ -68,13 +68,17 @@ func getPools(kstatPath string) ([]poolInfo, error) {
 }
 
 func getTags(pools []poolInfo) map[string]string {
-	var poolNames string
-
-	for _, pool := range pools {
-		if len(poolNames) != 0 {
-			poolNames += "::"
+	poolNames := ""
+	knownPools := make(map[string]struct{})
+	for _, entry := range pools {
+		name := entry.name
+		if _, ok := knownPools[name]; !ok {
+			knownPools[name] = struct{}{}
+			if poolNames != "" {
+				poolNames += "::"
+			}
+			poolNames += name
 		}
-		poolNames += pool.name
 	}
 
 	return map[string]string{"pools": poolNames}

plugins/inputs/zfs/zfs_linux_test.go

@@ -4,6 +4,7 @@
 package zfs
 
 import (
+	"fmt"
 	"os"
 	"testing"
 
@@ -323,6 +324,43 @@ func TestZfsGeneratesMetrics(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestGetTags(t *testing.T) {
+	tests := []struct {
+		name     string
+		pools    []poolInfo
+		expected map[string]string
+	}{
+		{
+			"no pools",
+			[]poolInfo{},
+			map[string]string{"pools": ""},
+		},
+		{
+			"single pool",
+			[]poolInfo{
+				{"data", "/proc/spl/kstat/zfs/data/objset-0x9288", v2},
+			},
+			map[string]string{"pools": "data"},
+		},
+		{
+			"duplicate pool names",
+			[]poolInfo{
+				{"pool", "/proc/spl/kstat/zfs/pool/objset-0x23ce1", v2},
+				{"pool", "/proc/spl/kstat/zfs/pool/objset-0x2e", v2},
+				{"data", "/proc/spl/kstat/zfs/data/objset-0x9288", v2},
+			},
+			map[string]string{"pools": "pool::data"},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(fmt.Sprintf(tc.name), func(t *testing.T) {
+			tags := getTags(tc.pools)
+			require.Equal(t, tc.expected, tags)
+		})
+	}
+}
+
 func getKstatMetricsArcOnly() map[string]interface{} {
 	return map[string]interface{}{
 		"arcstats_hits":                     int64(5968846374),