dsl_dir_space_towrite
used += dsl_dir_space_towrite(dd);
uint64_t est_inflight = dsl_dir_space_towrite(dd);
static uint64_t dsl_dir_space_towrite(dsl_dir_t *dd);
est_used = dsl_dir_space_towrite(dd) + dsl_dir_phys(dd)->dd_used_bytes;
towrite = dsl_dir_space_towrite(ds->ds_dir);