).si_then([this, FNAME, offset, &t](auto result) -> ref_ret {
DEBUGT("extent refcount is decremented to {} -- {}~{}, {}",
t, result.refcount, offset, result.length, result.addr);
).si_then([this, FNAME, offset, &t](auto result) -> ref_ret {
DEBUGT("extent refcount is decremented to {} -- {}~{}, {}",
t, result.refcount, offset, result.length, result.addr);