Writes bytes from the source `VmReader` to the user space of the current process. If the writing is completely successful, returns `Ok`. Otherwise, it returns `Err`. If the source `VmReader` (`src`) is empty, this function still checks if the current task and user space are available. If they are, it returns `Ok`.
(&self, dest: Vaddr, src: &mut VmReader<'_, Infallible>)
source not stored for this graph (policy: none)