[[!comment format=mdwn
 username="joey"
 subject="""comment 3"""
 date="2019-08-13T19:14:41Z"
 content="""
No, it cannot in general rely on that. Consider a file transfer program
that allocates the whole file full of 0 to start.

This needs to be reproduced in strace so we can see what it happening with
rsync.
"""]]
