Merge pull request #1348 from ncdc/fix-dmsetup-status-parsing-for-thin-ls

Fix detection of devmapper metadata reservation

devicemapper/thin_pool_watcher.go

@@ -150,8 +150,8 @@ func (w *ThinPoolWatcher) Refresh() error {
 }
 
 const (
-	thinPoolDmsetupStatusTokens           = 11
 	thinPoolDmsetupStatusHeldMetadataRoot = 6
+	thinPoolDmsetupStatusMinFields        = thinPoolDmsetupStatusHeldMetadataRoot + 1
 )
 
 // checkReservation checks to see whether the thin device is currently holding
@@ -163,14 +163,14 @@ func (w *ThinPoolWatcher) checkReservation(poolName string) (bool, error) {
 		return false, err
 	}
 
-	tokens := strings.Split(string(output), " ")
-	// Split returns the input as the last item in the result, adjust the
-	// number of tokens by one
-	if len(tokens) != thinPoolDmsetupStatusTokens+1 {
-		return false, fmt.Errorf("unexpected output of dmsetup status command; expected 11 fields, got %v; output: %v", len(tokens), string(output))
+	// we care about the field at fields[thinPoolDmsetupStatusHeldMetadataRoot],
+	// so make sure we get enough fields
+	fields := strings.Fields(string(output))
+	if len(fields) < thinPoolDmsetupStatusMinFields {
+		return false, fmt.Errorf("unexpected output of dmsetup status command; expected at least %d fields, got %v; output: %v", thinPoolDmsetupStatusMinFields, len(fields), string(output))
 	}
 
-	heldMetadataRoot := tokens[thinPoolDmsetupStatusHeldMetadataRoot]
+	heldMetadataRoot := fields[thinPoolDmsetupStatusHeldMetadataRoot]
 	currentlyReserved := heldMetadataRoot != "-"
 	return currentlyReserved, nil
 }

devicemapper/thin_pool_watcher_test.go

@@ -45,6 +45,18 @@ func TestRefresh(t *testing.T) {
 			},
 			expectedError: true,
 		},
+		{
+			name: "no existing reservation - ok with minimum # of fields",
+			dmsetupCommands: []fake.DmsetupCommand{
+				{"status", "0 75497472 thin-pool 65 327/524288 14092/589824 -", nil}, // status check
+				{"message", "", nil},                                                 // make reservation
+				{"message", "", nil},                                                 // release reservation
+			},
+			thinLsOutput:  usage,
+			expectedError: false,
+			deviceId:      "2",
+			expectedUsage: 23456,
+		},
 		{
 			name: "no existing reservation - ok",
 			dmsetupCommands: []fake.DmsetupCommand{
@@ -182,11 +194,6 @@ func TestCheckReservation(t *testing.T) {
 			statusResult:   "0 75 thin-pool 65 327/12345 14092/589824 - rw no_discard_passdown queue_if_no_space - ",
 			expectedResult: false,
 		},
-		{
-			name:         "malformed input",
-			statusResult: "0 12345 14092/45678 36 rw discard_passdown error_if_no_space needs_check ",
-			expectedErr:  fmt.Errorf("not gonna work"),
-		},
 	}
 
 	for _, tc := range cases {