[Yaffs] The issues about porting yaffs2 to STM32

Dear all,

I'm a newcomer to Yaffs2. Now I want to port yaffs2 to STM32. But I met an issue which confused me.

struct yaffs_dev {
                struct yaffs_param param;
                struct yaffs_driver drv;
                struct yaffs_tags_handler tagger;
...
}

When I port, I need to add some access functions. What's the difference between drv->write_chunk_fn and tagger->write_chunk_tags_fn (The same question is about read function)?
I think that the access function seems to be all WriteChunkToNandWithTags.
In the initialization code, the code check the drv's functions and tagger's functions for Yaffs2.

Best Regards,
Ray Li