What is this long cylindrical white fruit called?
It appears this is a Kigela (and commonly referred to as a &quot;Sausage tree&quot; in English).

It is - as you suspected - considered inedible and even poisonous in its fresh form (but apparently it can be dried or fermented). It has, as you said, a hard shell which can make this fruit usable as a container after it is hollowed-out.
The wikipedia article on this tree says it grows throughout tropical Africa, but looking at iNaturalist, it has been observed growing all over the world: