Function add_execute_where_read 

pub fn add_execute_where_read(mode: u32) -> u32

Add execute wherever read is already granted — exactly chmod a+X.

A directory’s execute bit means “may be traversed”, so a directory with read but no execute can be listed and not entered, which is almost never what anyone wants. Note this deliberately does not grant execute to classes that have no read: forcing o+x on everything would widen /root (0700), ~/.ssh (0700) and /etc/ssl/private — a real security regression, not a convenience.