Long running trills are made with \startTrillSpan and
\stopTrillSpan,
\new Voice {
<< { c1 \startTrillSpan }
{ s2. \grace { d16[\stopTrillSpan e] } } >>
c4 }
\startTrillSpan,
\stopTrillSpan.
Program reference: TrillSpanner, TrillSpanEvent.
This page is for LilyPond-2.4.5 (stable-branch).