> What I'm looking for:
> 
>   - Whether you like it or not;
>   - Comments on the interface and possible improvements;
>   - Anything else you have in mind.

- "metahook" sounds like a confusing name.  (sorry, no alternative suggestion.)
- it's better to make metahhook-id an opaque type rather than a plain int.
- how does it handle fileid recycles?
- "inode" is a filesystem dependent term.
- using dev_t here seems weird to me.  isn't it better to use
  a pointer to struct mount?
- why ignore hashmask returned by hashinit?
- what's a locking strategy?  "leave it callers"?
- metahook_inode_delete and metahook_table_delete seem to use
  "mhe" after freeing.
- i don't think M_TEMP is appropriate.
- 0 and 1 should be METAHOOK_CLEANUP_* ?

YAMAMOTO Takashi