Fix format migration regression (#5668)

Migration regression got introduced in 9083bc152e
adding more unit tests to catch this scenario, we need to fix this by
re-writing the formats after the migration to 'V3'.

This bug only happens when a user is migrating directly from V1 to V3,
not from V1 to V2 and V2 to V3.

Added additional unit tests to cover these situations as well.

Fixes #5667

cmd/format-xl_test.go

@@ -18,10 +18,12 @@ package cmd
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"os"
+	"reflect"
 	"testing"
+
+	"github.com/minio/minio/pkg/errors"
 )
 
 // Test get offline/online uuids.
@@ -74,6 +76,73 @@ func TestGetUUIDs(t *testing.T) {
 	}
 }
 
+// tests fixFormatXLV3 - fix format.json on all disks.
+func TestFixFormatV3(t *testing.T) {
+	xlDirs, err := getRandomDisks(8)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, xlDir := range xlDirs {
+		defer os.RemoveAll(xlDir)
+	}
+	endpoints := mustGetNewEndpointList(xlDirs...)
+
+	format := newFormatXLV3(1, 8)
+	formats := make([]*formatXLV3, 8)
+
+	for j := 0; j < 8; j++ {
+		newFormat := *format
+		newFormat.XL.This = format.XL.Sets[0][j]
+		formats[j] = &newFormat
+	}
+
+	if err = initFormatXLMetaVolume(endpoints, formats); err != nil {
+		t.Fatal(err)
+	}
+
+	formats[1] = nil
+	expThis := formats[2].XL.This
+	formats[2].XL.This = ""
+	if err := fixFormatXLV3(endpoints, formats); err != nil {
+		t.Fatal(err)
+	}
+	newFormats, errs := loadFormatXLAll(endpoints)
+	for _, err := range errs {
+		if err != nil && errors.Cause(err) != errUnformattedDisk {
+			t.Fatal(err)
+		}
+	}
+	gotThis := newFormats[2].XL.This
+	if expThis != gotThis {
+		t.Fatalf("expected uuid %s, got %s", expThis, gotThis)
+	}
+}
+
+// tests formatXLV3ThisEmpty conditions.
+func TestFormatXLEmpty(t *testing.T) {
+	format := newFormatXLV3(1, 16)
+	formats := make([]*formatXLV3, 16)
+
+	for j := 0; j < 16; j++ {
+		newFormat := *format
+		newFormat.XL.This = format.XL.Sets[0][j]
+		formats[j] = &newFormat
+	}
+
+	// empty format to indicate disk not found, but this
+	// empty should return false.
+	formats[0] = nil
+
+	if ok := formatXLV3ThisEmpty(formats); ok {
+		t.Fatalf("expected value false, got %t", ok)
+	}
+
+	formats[2].XL.This = ""
+	if ok := formatXLV3ThisEmpty(formats); !ok {
+		t.Fatalf("expected value true, got %t", ok)
+	}
+}
+
 // Tests format xl get version.
 func TestFormatXLGetVersion(t *testing.T) {
 	// Get test root.
@@ -201,7 +270,25 @@ func TestFormatXLMigrate(t *testing.T) {
 		t.Fatal(err)
 	}
 	if migratedVersion != formatXLVersionV3 {
-		t.Fatal(fmt.Sprintf("expected version: %s, got: %s", formatXLVersionV3, migratedVersion))
+		t.Fatalf("expected version: %s, got: %s", formatXLVersionV3, migratedVersion)
+	}
+
+	b, err = ioutil.ReadFile(pathJoin(rootPath, minioMetaBucket, formatConfigFile))
+	if err != nil {
+		t.Fatal(err)
+	}
+	formatV3 := &formatXLV3{}
+	if err = json.Unmarshal(b, formatV3); err != nil {
+		t.Fatal(err)
+	}
+	if formatV3.XL.This != m.XL.Disk {
+		t.Fatalf("expected disk uuid: %s, got: %s", m.XL.Disk, formatV3.XL.This)
+	}
+	if len(formatV3.XL.Sets) != 1 {
+		t.Fatalf("expected single set after migrating from v1 to v3, but found %d", len(formatV3.XL.Sets))
+	}
+	if !reflect.DeepEqual(formatV3.XL.Sets[0], m.XL.JBOD) {
+		t.Fatalf("expected disk uuid: %v, got: %v", m.XL.JBOD, formatV3.XL.Sets[0])
 	}
 
 	m = &formatXLV1{}