Initial QSfera import

Server/vendor/github.com/dgraph-io/ristretto/z/file_linux.go

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2020 Dgraph Labs, Inc. and Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package z
+
+import (
+	"fmt"
+)
+
+// Truncate would truncate the mmapped file to the given size. On Linux, we truncate
+// the underlying file and then call mremap, but on other systems, we unmap first,
+// then truncate, then re-map.
+func (m *MmapFile) Truncate(maxSz int64) error {
+	if err := m.Sync(); err != nil {
+		return fmt.Errorf("while sync file: %s, error: %v\n", m.Fd.Name(), err)
+	}
+	if err := m.Fd.Truncate(maxSz); err != nil {
+		return fmt.Errorf("while truncate file: %s, error: %v\n", m.Fd.Name(), err)
+	}
+
+	var err error
+	m.Data, err = mremap(m.Data, int(maxSz)) // Mmap up to max size.
+	return err
+}