archiver: only store deviceID for hardlinks

The deviceID can change e.g. when backing up from filesystem snapshot.
It is only used for hardlink detection. Thus there it is not necessary
to store it for everything else.

internal/archiver/archiver.go

@@ -188,6 +188,12 @@ func (arch *Archiver) nodeFromFileInfo(snPath, filename string, fi os.FileInfo)
 	if !arch.WithAtime {
 		node.AccessTime = node.ModTime
 	}
+	if node.Links == 1 || node.Type == "dir" {
+		// the DeviceID is only necessary for hardlinked files
+		// when using subvolumes or snapshots their deviceIDs tend to change which causes
+		// restic to upload new tree blobs
+		node.DeviceID = 0
+	}
 	// overwrite name to match that within the snapshot
 	node.Name = path.Base(snPath)
 	if err != nil {

internal/archiver/archiver_test.go

@@ -2153,6 +2153,7 @@ func TestMetadataChanged(t *testing.T) {
 	sn, node2 := snapshot(t, repo, fs, nil, "testfile")
 
 	// set some values so we can then compare the nodes
+	want.DeviceID = 0
 	want.Content = node2.Content
 	want.Path = ""
 	if len(want.ExtendedAttributes) == 0 {

internal/restic/node.go

@@ -82,7 +82,7 @@ type Node struct {
 	User       string      `json:"user,omitempty"`
 	Group      string      `json:"group,omitempty"`
 	Inode      uint64      `json:"inode,omitempty"`
-	DeviceID   uint64      `json:"device_id,omitempty"` // device id of the file, stat.st_dev
+	DeviceID   uint64      `json:"device_id,omitempty"` // device id of the file, stat.st_dev, only stored for hardlinks
 	Size       uint64      `json:"size,omitempty"`
 	Links      uint64      `json:"links,omitempty"`
 	LinkTarget string      `json:"linktarget,omitempty"`