fuse_lowlevel implemention

`fuse_lowlevel`几乎所有的接口都需要一个`inode号（unsigned long）`作为参数，不同于本地文件系统的是，在BFS中好像是通过文件的`路径名（BfsFileInfo.name）`来唯一确定一个文件，并没有inode号这个概念，是否可以使用文件路径名的ASCII码来作为fuse_lowlevel接口需要的inode号？但是这样的问题是BFS从根本上不支持link操作。

Start by reviewing the fuse_lowlevel interfaces and the BFS file identity represented by BfsFileInfo.name. Determine whether a stable inode mapping can support the required operations, including link, and document the chosen identity and its limitations; the issue mentions no specific files or tests.

Written by the indexing model from the issue text.