mufs: properly sync file size and check file size in mufs_write() and mufs_read() respectively

source/fs/mufs/file.c

@@ -96,6 +96,9 @@ size_t mufs_read(struct mufs_file *file, void *data, size_t len)
 	if (!(file->mode & MUFS_READ))
 		return 0;
 
+	if (file->va >= file->tree->file_size)
+		return 0;
+
 	if (!(ret = mufs_tree_read(file->tree, data, file->va, len)))
 		return 0;
 
@@ -122,8 +125,12 @@ size_t mufs_write(struct mufs_file *file, const void *data, size_t len)
 
 	file->va += ret;
 
-	if (file->tree->file_size <= file->va && mufs_sync_tree(file->tree) < 0)
-		return 0;
+	if (file->tree->file_size <= file->va) {
+		file->tree->file_size = file->va;
+
+		if (mufs_sync_tree(file->tree) < 0)
+			return 0;
+	}
 
 	return ret;
 }