anchor.diff:                 (iobuf-end-space-length iobuf))
       (isys:ewouldblock () nil)))
   
  -(declaim (notinline %fill-ibuf/no-hang))
  +(declaim (inline %fill-ibuf/no-hang))
   (defun %fill-ibuf/no-hang (iobuf fd read-fn)
     (declare (type iobuf iobuf))
     (let ((nbytes (%read-once/no-hang fd read-fn iobuf)))
  
positive.code: ;;; Input
  ;;;-------------------------------------------------------------------------
  
  (declaim (notinline %read-once))
  (defun %read-once (fd read-fn iobuf)
    (declare (type function read-fn)
             (type iobuf iobuf))
  
negative.code:       (isys:ewouldblock ()
          (iomux:wait-until-fd-ready fd :input nil t)))))
  
  (declaim (inline %fill-ibuf))
  (defun %fill-ibuf (iobuf fd read-fn)
    (declare (type iobuf iobuf))
    (let ((nbytes (%read-once fd read-fn iobuf)))
  