fusefrontend: report an error if all files in a directory were invalid

Just presenting an empty directory means that the user does not know
that things went wrong unless he checks the syslog or tries to delete
the directory.

It would be nice to report the error even if only some files were
invalid. However, go-fuse does not allow returning the valid
directory entries AND an error.

internal/fusefrontend/fs_dir.go

@@ -226,8 +226,11 @@ func (fs *FS) OpenDir(dirName string, context *fuse.Context) ([]fuse.DirEntry, f
 			return nil, fuse.ToStatus(err)
 		}
 	}
-	// Filter and decrypt filenames
+
+	// Decrypted directory entries
 	var plain []fuse.DirEntry
+	var errorCount int
+	// Filter and decrypt filenames
 	for i := range cipherEntries {
 		cName := cipherEntries[i].Name
 		if dirName == "" && cName == configfile.ConfDefaultName {
@@ -244,29 +247,44 @@ func (fs *FS) OpenDir(dirName string, context *fuse.Context) ([]fuse.DirEntry, f
 			continue
 		}
 
+		// Handle long file name
+		isLong := nametransform.LongNameNone
 		if fs.args.LongNames {
-			isLong := nametransform.NameType(cName)
-			if isLong == nametransform.LongNameContent {
-				cNameLong, err := nametransform.ReadLongName(filepath.Join(cDirAbsPath, cName))
-				if err != nil {
-					toggledlog.Warn.Printf("Could not read long name for file %s, skipping file", cName)
-					continue
-				}
-				cName = cNameLong
-			} else if isLong == nametransform.LongNameFilename {
-				// ignore "gocryptfs.longname.*.name"
+			isLong = nametransform.NameType(cName)
+		}
+		if isLong == nametransform.LongNameContent {
+			cNameLong, err := nametransform.ReadLongName(filepath.Join(cDirAbsPath, cName))
+			if err != nil {
+				toggledlog.Warn.Printf("Skipping file %q in dir %q: Could not read .name: %v",
+					cName, cDirName, err)
+				errorCount++
 				continue
 			}
+			cName = cNameLong
+		} else if isLong == nametransform.LongNameFilename {
+			// ignore "gocryptfs.longname.*.name"
+			continue
 		}
+
 		name, err := fs.nameTransform.DecryptName(cName, cachedIV)
 		if err != nil {
-			toggledlog.Warn.Printf("Skipping invalid name '%s' in dir '%s': %s",
+			toggledlog.Warn.Printf("Skipping invalid name %q in dir %q: %s",
 				cName, cDirName, err)
+			errorCount++
 			continue
 		}
 
 		cipherEntries[i].Name = name
 		plain = append(plain, cipherEntries[i])
 	}
+
+	if errorCount > 0 && len(plain) == 0 {
+		// Don't let the user stare on an empty directory. Report that things went
+		// wrong.
+		toggledlog.Warn.Printf("All %d entries in directory %q were invalid, returning EIO",
+			errorCount, cDirName)
+		status = fuse.EIO
+	}
+
 	return plain, status
 }