api: Introduce metadata update APIs to update only metadata (#11962)

Current implementation heavily relies on readAllFileInfo
but with the advent of xl.meta inlined with data, we cannot
easily avoid reading data when we are only interested is
updating metadata, this leads to invariably write
amplification during metadata updates, repeatedly reading
data when we are only interested in updating metadata.

This PR ensures that we implement a metadata only update
API at storage layer, that handles updates to metadata alone
for any given version - given the version is valid and
present.

This helps reduce the chattiness for following calls..

- PutObjectTags
- DeleteObjectTags
- PutObjectLegalHold
- PutObjectRetention
- ReplicateObject (updates metadata on replication status)

cmd/xl-storage.go

@@ -897,6 +897,44 @@ func (s *xlStorage) DeleteVersion(ctx context.Context, volume, path string, fi F
 	return err
 }
 
+// Updates only metadata for a given version.
+func (s *xlStorage) UpdateMetadata(ctx context.Context, volume, path string, fi FileInfo) error {
+	if len(fi.Metadata) == 0 {
+		return errInvalidArgument
+	}
+
+	buf, err := s.ReadAll(ctx, volume, pathJoin(path, xlStorageFormatFile))
+	if err != nil {
+		if err == errFileNotFound {
+			if fi.VersionID != "" {
+				return errFileVersionNotFound
+			}
+		}
+		return err
+	}
+
+	if !isXL2V1Format(buf) {
+		return errFileVersionNotFound
+	}
+
+	var xlMeta xlMetaV2
+	if err = xlMeta.Load(buf); err != nil {
+		logger.LogIf(ctx, err)
+		return err
+	}
+
+	if err = xlMeta.UpdateObjectVersion(fi); err != nil {
+		return err
+	}
+
+	buf, err = xlMeta.AppendTo(nil)
+	if err != nil {
+		return err
+	}
+
+	return s.WriteAll(ctx, volume, pathJoin(path, xlStorageFormatFile), buf)
+}
+
 // WriteMetadata - writes FileInfo metadata for path at `xl.meta`
 func (s *xlStorage) WriteMetadata(ctx context.Context, volume, path string, fi FileInfo) error {
 	buf, err := s.ReadAll(ctx, volume, pathJoin(path, xlStorageFormatFile))
@@ -936,7 +974,6 @@ func (s *xlStorage) WriteMetadata(ctx context.Context, volume, path string, fi F
 	}
 
 	return s.WriteAll(ctx, volume, pathJoin(path, xlStorageFormatFile), buf)
-
 }
 
 func (s *xlStorage) renameLegacyMetadata(volumeDir, path string) (err error) {
@@ -1044,7 +1081,7 @@ func (s *xlStorage) ReadVersion(ctx context.Context, volume, path, versionID str
 
 		// Reading data for small objects when
 		// - object has not yet transitioned
-		// - object size lesser than 32KiB
+		// - object size lesser than 128KiB
 		// - object has maximum of 1 parts
 		if fi.TransitionStatus == "" && fi.DataDir != "" && fi.Size <= smallFileThreshold && len(fi.Parts) == 1 {
 			// Enable O_DIRECT optionally only if drive supports it.
@@ -1891,7 +1928,7 @@ func (s *xlStorage) RenameData(ctx context.Context, srcVolume, srcPath, dataDir,
 		if isXL2V1Format(dstBuf) {
 			if err = xlMeta.Load(dstBuf); err != nil {
 				logger.LogIf(s.ctx, err)
-				return errFileCorrupt
+				return err
 			}
 		} else {
 			// This code-path is to preserve the legacy data.