* read db_data, dmu_buf_will_dirty() before modifying it, and the
* object must be held in an assigned transaction before calling
* dmu_buf_will_dirty. You may use dmu_buf_set_user() on the bonus
* read db_data, dmu_buf_will_dirty() before modifying it, and the
* object must be held in an assigned transaction before calling
* dmu_buf_will_dirty. You may use dmu_buf_set_user() on the bonus