Function chunking_from_layer_committed 

fn chunking_from_layer_committed(
    repo: &Repo,
    l: &Descriptor,
    chunking: &mut Chunking,
) -> Result<()>

The way we store “chunk” layers in ostree is by writing a commit whose filenames are their own object identifier. This function parses what is written by the ImporterMode::ObjectSet logic, turning it back into a “chunked” structure that is used by the export code.