Add a new method to the ObjectStore that takes a path to a file
system tree, which is currently being built, and commits it to
the store and references it via a given object_id.
The tree is copied to a temporary location (co-located in the
store to enable fast copying via reflinks) and then atomically
moved into the ObjectStore's objects path via rename(3).
Extract the code from ObjectStore.new that will commit the filled
tree to the store into its own method so it can be used from a
future method to snapshot trees at random points in time.
Introduce a small `TreeObject` class that is the representation of
a tree during its construction. It supports calculating its treesum
as well initialize the new tree with an existing one.
Import modules between files using the syntax `from . import foobar`,
renaming what used to be `FooBar` to `foobar.FooBar` when moved to a
separate file.
In __init__.py only import what is meant to be public API.
Signed-off-by: Tom Gundersen <teg@jklm.no>
