What is an efficient way to get all blobs / trees that have notes attached?

[Sebastian Schuberth <sschuberth@gmail.com>]

Hi,

I'm curious whether there's a more efficient way to get a list of blobs 
/ trees (and their names) that have notes attached than doing this:

1) Get all notes refs I'm interested in (git-for-each-ref).

2) For each notes ref, get the list of notes (git-notes list) and store 
them in a hash table that maps object hashes to notes.

3) Recursively list all blobs / trees (git-ls-tree) and look whether an 
object's hash is conatined in our table to get its notes.

In particular 3) could be expensive for repos with a lot of files as 
we're looking at all of them just to see whether they have notes attached.

Regards,
Sebastian