Add sync mode for 'xl.json' (#6798)

xl.json is the source of truth for all erasure
coded objects, without which we won't be able to
read the objects properly. This PR enables sync
mode for writing `xl.json` such all writes go hit
the disk and are persistent under situations such
as abrupt power failures on servers running Minio.

cmd/naughty-disk_test.go

@@ -159,6 +159,13 @@ func (d *naughtyDisk) DeleteFile(volume string, path string) (err error) {
 	return d.disk.DeleteFile(volume, path)
 }
 
+func (d *naughtyDisk) WriteAll(volume string, path string, buf []byte) (err error) {
+	if err := d.calcError(); err != nil {
+		return err
+	}
+	return d.disk.WriteAll(volume, path, buf)
+}
+
 func (d *naughtyDisk) ReadAll(volume string, path string) (buf []byte, err error) {
 	if err := d.calcError(); err != nil {
 		return nil, err

cmd/posix.go

@@ -847,7 +847,7 @@ func (s *posix) ReadFile(volume, path string, offset int64, buffer []byte, verif
 	return int64(len(buffer)), nil
 }
 
-func (s *posix) createFile(volume, path string) (f *os.File, err error) {
+func (s *posix) openFile(volume, path string, mode int) (f *os.File, err error) {
 	defer func() {
 		if err == errFaultyDisk {
 			atomic.AddInt32(&s.ioErrCount, 1)
@@ -896,7 +896,7 @@ func (s *posix) createFile(volume, path string) (f *os.File, err error) {
 		}
 	}
 
-	w, err := os.OpenFile(filePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0666)
+	w, err := os.OpenFile(filePath, mode, 0666)
 	if err != nil {
 		// File path cannot be verified since one of the parents is a file.
 		switch {
@@ -941,7 +941,7 @@ func (s *posix) PrepareFile(volume, path string, fileSize int64) (err error) {
 	}
 
 	// Create file if not found
-	w, err := s.createFile(volume, path)
+	w, err := s.openFile(volume, path, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
 	if err != nil {
 		return err
 	}
@@ -972,6 +972,30 @@ func (s *posix) PrepareFile(volume, path string, fileSize int64) (err error) {
 	return nil
 }
 
+func (s *posix) WriteAll(volume, path string, buf []byte) (err error) {
+	defer func() {
+		if err == errFaultyDisk {
+			atomic.AddInt32(&s.ioErrCount, 1)
+		}
+	}()
+
+	if atomic.LoadInt32(&s.ioErrCount) > maxAllowedIOError {
+		return errFaultyDisk
+	}
+
+	// Create file if not found
+	w, err := s.openFile(volume, path, os.O_CREATE|os.O_SYNC|os.O_WRONLY)
+	if err != nil {
+		return err
+	}
+
+	if _, err = w.Write(buf); err != nil {
+		return err
+	}
+
+	return w.Close()
+}
+
 // AppendFile - append a byte array at path, if file doesn't exist at
 // path this call explicitly creates it.
 func (s *posix) AppendFile(volume, path string, buf []byte) (err error) {
@@ -986,15 +1010,18 @@ func (s *posix) AppendFile(volume, path string, buf []byte) (err error) {
 	}
 
 	// Create file if not found
-	w, err := s.createFile(volume, path)
+	w, err := s.openFile(volume, path, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
 	if err != nil {
 		return err
 	}
-	_, err = w.Write(buf)
-	w.Close()
+
+	if _, err = w.Write(buf); err != nil {
 		return err
 	}
 
+	return w.Close()
+}
+
 // StatFile - get file info.
 func (s *posix) StatFile(volume, path string) (file FileInfo, err error) {
 	defer func() {

cmd/storage-interface.go

@@ -47,6 +47,9 @@ type StorageAPI interface {
 	StatFile(volume string, path string) (file FileInfo, err error)
 	DeleteFile(volume string, path string) (err error)
 
+	// Write all data, syncs the data to disk.
+	WriteAll(volume string, path string, buf []byte) (err error)
+
 	// Read all.
 	ReadAll(volume string, path string) (buf []byte, err error)
 }

cmd/storage-rest-client.go

@@ -221,6 +221,17 @@ func (client *storageRESTClient) AppendFile(volume, path string, buffer []byte)
 	return err
 }
 
+// WriteAll - write all data to a file.
+func (client *storageRESTClient) WriteAll(volume, path string, buffer []byte) error {
+	values := make(url.Values)
+	values.Set(storageRESTVolume, volume)
+	values.Set(storageRESTFilePath, path)
+	reader := bytes.NewBuffer(buffer)
+	respBody, err := client.call(storageRESTMethodWriteAll, values, reader)
+	defer CloseResponse(respBody)
+	return err
+}
+
 // StatFile - stat a file.
 func (client *storageRESTClient) StatFile(volume, path string) (info FileInfo, err error) {
 	values := make(url.Values)

cmd/storage-rest-common.go

@@ -28,6 +28,7 @@ const (
 
 	storageRESTMethodPrepareFile = "preparefile"
 	storageRESTMethodAppendFile  = "appendfile"
+	storageRESTMethodWriteAll    = "writeall"
 	storageRESTMethodStatFile    = "statfile"
 	storageRESTMethodReadAll     = "readall"
 	storageRESTMethodReadFile    = "readfile"

cmd/storage-rest-server.go

@@ -179,6 +179,33 @@ func (s *storageRESTServer) AppendFileHandler(w http.ResponseWriter, r *http.Req
 	}
 }
 
+// WriteAllHandler - write to file all content.
+func (s *storageRESTServer) WriteAllHandler(w http.ResponseWriter, r *http.Request) {
+	if !s.IsValid(w, r) {
+		return
+	}
+	vars := mux.Vars(r)
+	volume := vars[storageRESTVolume]
+	filePath := vars[storageRESTFilePath]
+
+	if r.ContentLength < 0 {
+		s.writeErrorResponse(w, errInvalidArgument)
+		return
+	}
+
+	buf := make([]byte, r.ContentLength)
+	_, err := io.ReadFull(r.Body, buf)
+	if err != nil {
+		s.writeErrorResponse(w, err)
+		return
+	}
+
+	err = s.storage.WriteAll(volume, filePath, buf)
+	if err != nil {
+		s.writeErrorResponse(w, err)
+	}
+}
+
 // StatFileHandler - stat a file.
 func (s *storageRESTServer) StatFileHandler(w http.ResponseWriter, r *http.Request) {
 	if !s.IsValid(w, r) {
@@ -336,6 +363,8 @@ func registerStorageRESTHandlers(router *mux.Router, endpoints EndpointList) {
 			Queries(restQueries(storageRESTVolume, storageRESTFilePath, storageRESTLength)...)
 		subrouter.Methods(http.MethodPost).Path("/" + storageRESTMethodAppendFile).HandlerFunc(httpTraceHdrs(server.AppendFileHandler)).
 			Queries(restQueries(storageRESTVolume, storageRESTFilePath)...)
+		subrouter.Methods(http.MethodPost).Path("/" + storageRESTMethodWriteAll).HandlerFunc(httpTraceHdrs(server.WriteAllHandler)).
+			Queries(restQueries(storageRESTVolume, storageRESTFilePath)...)
 		subrouter.Methods(http.MethodPost).Path("/" + storageRESTMethodStatFile).HandlerFunc(httpTraceHdrs(server.StatFileHandler)).
 			Queries(restQueries(storageRESTVolume, storageRESTFilePath)...)
 		subrouter.Methods(http.MethodPost).Path("/" + storageRESTMethodReadAll).HandlerFunc(httpTraceHdrs(server.ReadAllHandler)).

cmd/xl-v1-metadata.go

@@ -423,8 +423,9 @@ func writeXLMetadata(ctx context.Context, disk StorageAPI, bucket, prefix string
 		logger.LogIf(ctx, err)
 		return err
 	}
+
 	// Persist marshaled data.
-	err = disk.AppendFile(bucket, jsonFile, metadataBytes)
+	err = disk.WriteAll(bucket, jsonFile, metadataBytes)
 	logger.LogIf(ctx, err)
 	return err
 }