inomap: fix spillBit not set on 2nd hit

Also add a test for this.

Thanks @slackner for the comment.

internal/inomap/inomap.go

@@ -27,6 +27,8 @@ const (
 	maxPassthruIno = 1<<48 - 1
 	// max value of 63 bit spill inode number
 	maxSpillIno = 1<<63 - 1
+	// bit 63 is used as the spill bit
+	spillBit = 1 << 63
 )
 
 // InoMap stores the maps using for inode number translation.
@@ -57,7 +59,7 @@ func New() *InoMap {
 func (m *InoMap) spill(in QIno) (out uint64) {
 	out, found := m.spillMap[in]
 	if found {
-		return out
+		return out | spillBit
 	}
 	if m.spillNext >= maxSpillIno {
 		log.Panicf("spillMap overflow: spillNext = 0x%x", m.spillNext)
@@ -65,7 +67,7 @@ func (m *InoMap) spill(in QIno) (out uint64) {
 	out = m.spillNext
 	m.spillNext++
 	m.spillMap[in] = out
-	return 1<<63 | out
+	return out | spillBit
 }
 
 // Translate maps the passed-in (device, inode) pair to a unique inode number.

internal/inomap/inomap_test.go

@@ -99,6 +99,23 @@ func TestTranslateStress(t *testing.T) {
 	}
 }
 
+func TestSpill(t *testing.T) {
+	m := New()
+	var q QIno
+	q.Ino = maxPassthruIno + 1
+	out1 := m.Translate(q)
+	if out1|spillBit == 0 {
+		t.Error("spill bit not set")
+	}
+	out2 := m.Translate(q)
+	if out2|spillBit == 0 {
+		t.Error("spill bit not set")
+	}
+	if out1 != out2 {
+		t.Errorf("unstable mapping: %d vs %d", out1, out2)
+	}
+}
+
 // TestUniqueness checks that unique (Dev, Flags, Ino) tuples get unique inode
 // numbers
 func TestUniqueness(t *testing.T) {