XL: Don't return ignored errors in listDirFactory (#3935)

Previously, erasure backend's `listDirFactory` may return errors which
were explicitly ignored. With this change, it returns nil. Superfluous
checks at higher-layers for ignored errors are removed as well.

cmd/tree-walk_test.go

@@ -348,10 +348,12 @@ func TestListDir(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	// None of the disks are available, should get errDiskNotFound.
+	// None of the disks are available, should get
+	// errDiskNotFound. Since errDiskNotFound is an ignored error,
+	// we should get nil.
 	_, _, err = listDir(volume, "", "")
-	if errorCause(err) != errDiskNotFound {
-		t.Error("expected errDiskNotFound error.")
+	if err != nil {
+		t.Errorf("expected nil error but found %v.", err)
 	}
 }
 

cmd/xl-v1-list-objects-heal.go

@@ -107,10 +107,6 @@ func (xl xlObjects) listObjectsHeal(bucket, prefix, marker, delimiter string, ma
 		}
 		// For any walk error return right away.
 		if walkResult.err != nil {
-			// File not found is a valid case.
-			if walkResult.err == errFileNotFound {
-				return ListObjectsInfo{}, nil
-			}
 			return ListObjectsInfo{}, toObjectErr(walkResult.err, bucket, prefix)
 		}
 		entry := walkResult.entry
@@ -325,12 +321,6 @@ func (xl xlObjects) listMultipartUploadsHeal(bucket, prefix, keyMarker,
 		}
 		// Collect uploads until maxUploads limit is reached.
 		for walkResult := range walkerCh {
-			// Ignore errors like errDiskNotFound
-			// and errFileNotFound.
-			if isErrIgnored(walkResult.err,
-				xlTreeWalkIgnoredErrs...) {
-				continue
-			}
 			// For any error during tree walk we should
 			// return right away.
 			if walkResult.err != nil {

cmd/xl-v1-list-objects.go

@@ -27,19 +27,20 @@ func listDirFactory(isLeaf isLeafFunc, treeWalkIgnoredErrs []error, disks ...Sto
 				continue
 			}
 			entries, err = disk.ListDir(bucket, prefixDir)
-			if err == nil {
-				entries, delayIsLeaf = filterListEntries(bucket, prefixDir, entries, prefixEntry, isLeaf)
-				return entries, delayIsLeaf, nil
-			}
-			// For any reason disk was deleted or goes offline, continue
-			// and list from other disks if possible.
-			if isErrIgnored(err, treeWalkIgnoredErrs...) {
-				continue
+			if err != nil {
+				// For any reason disk was deleted or goes offline, continue
+				// and list from other disks if possible.
+				if isErrIgnored(err, treeWalkIgnoredErrs...) {
+					continue
+				}
+				return nil, false, traceError(err)
 			}
-			break
+
+			entries, delayIsLeaf = filterListEntries(bucket, prefixDir, entries, prefixEntry, isLeaf)
+			return entries, delayIsLeaf, nil
 		}
-		// Return error at the end.
-		return nil, false, traceError(err)
+		// Nothing found in all disks
+		return nil, false, nil
 	}
 	return listDir
 }
@@ -73,10 +74,6 @@ func (xl xlObjects) listObjects(bucket, prefix, marker, delimiter string, maxKey
 		}
 		// For any walk error return right away.
 		if walkResult.err != nil {
-			// File not found is a valid case.
-			if errorCause(walkResult.err) == errFileNotFound {
-				return ListObjectsInfo{}, nil
-			}
 			return ListObjectsInfo{}, toObjectErr(walkResult.err, bucket, prefix)
 		}
 		entry := walkResult.entry

cmd/xl-v1-multipart.go

@@ -349,10 +349,6 @@ func (xl xlObjects) listMultipartUploads(bucket, prefix, keyMarker, uploadIDMark
 			}
 			// For any walk error return right away.
 			if walkResult.err != nil {
-				// File not found or Disk not found is a valid case.
-				if isErrIgnored(walkResult.err, xlTreeWalkIgnoredErrs...) {
-					continue
-				}
 				return ListMultipartsInfo{}, err
 			}
 			entry := strings.TrimPrefix(walkResult.entry, retainSlash(bucket))