fix(backup): skip loading the backingFile when doing backup or when u…

…ser request

exporting the volume without backingFile

longhorn-9209

Signed-off-by: Phan Le <phan.le@suse.com>

pkg/replica/diff_disk.go

@@ -20,7 +20,7 @@ type diffDisk struct {
 	// we don't know the location yet.
 	location []byte
 	// list of files in grandparent, parent, child, etc order.
-	// index 0 is nil or backing file and index n-1 is the active write layer
+	// index 0 is nil and index n-1 is the active write layer
 	files      []types.DiffDisk
 	sectorSize int64
 	// current size of the head file.
@@ -372,12 +372,17 @@ func (d *diffDisk) initializeSectorLocation(value byte) {
 	}
 }
 
-func (d *diffDisk) preload() error {
+func (d *diffDisk) preload(isThereBackingFile bool) error {
 	for i, f := range d.files {
 		if i == 0 {
 			continue
 		}
 
+		// Skip loading the backingFile if it exists
+		if i == int(backingFileIndex) && isThereBackingFile {
+			continue
+		}
+
 		if err := LoadDiffDiskLocationList(d, f, byte(i)); err != nil {
 			return err
 		}

pkg/replica/replica.go

@@ -1467,7 +1467,8 @@ func (r *Replica) Preload(includeBackingFileLayer bool) error {
 	} else {
 		r.volume.initializeSectorLocation(nilFileIndex)
 	}
-	return r.volume.preload()
+	isThereBackingFile := r.info.BackingFile != nil
+	return r.volume.preload(isThereBackingFile)
 }
 
 func (r *Replica) GetDataLayout(ctx context.Context) (<-chan sparse.FileInterval, <-chan error, error) {