all: Add copy-on-write filesystem support (fixes #4271) (#6746)

lib/fs/filesystem_copy_range_method.go

@@ -0,0 +1,60 @@
+// Copyright (C) 2020 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+type CopyRangeMethod int
+
+const (
+	CopyRangeMethodStandard CopyRangeMethod = iota
+	CopyRangeMethodIoctl
+	CopyRangeMethodCopyFileRange
+	CopyRangeMethodSendFile
+	CopyRangeMethodAllWithFallback
+)
+
+func (o CopyRangeMethod) String() string {
+	switch o {
+	case CopyRangeMethodStandard:
+		return "standard"
+	case CopyRangeMethodIoctl:
+		return "ioctl"
+	case CopyRangeMethodCopyFileRange:
+		return "copy_file_range"
+	case CopyRangeMethodSendFile:
+		return "sendfile"
+	case CopyRangeMethodAllWithFallback:
+		return "all"
+	default:
+		return "unknown"
+	}
+}
+
+func (o CopyRangeMethod) MarshalText() ([]byte, error) {
+	return []byte(o.String()), nil
+}
+
+func (o *CopyRangeMethod) UnmarshalText(bs []byte) error {
+	switch string(bs) {
+	case "standard":
+		*o = CopyRangeMethodStandard
+	case "ioctl":
+		*o = CopyRangeMethodIoctl
+	case "copy_file_range":
+		*o = CopyRangeMethodCopyFileRange
+	case "sendfile":
+		*o = CopyRangeMethodSendFile
+	case "all":
+		*o = CopyRangeMethodAllWithFallback
+	default:
+		*o = CopyRangeMethodStandard
+	}
+	return nil
+}
+
+func (o *CopyRangeMethod) ParseDefault(str string) error {
+	return o.UnmarshalText([]byte(str))
+}