dmu_buf_set_user
return (dmu_buf_set_user(db_fake, user));
winner = dmu_buf_set_user(&db->db, &dnc->dnc_dbu);
void *dmu_buf_set_user(dmu_buf_t *db, dmu_buf_user_t *user);
VERIFY3P(NULL, ==, dmu_buf_set_user(l->l_dbuf, &l->l_dbu));
zap_leaf_t *winner = dmu_buf_set_user(db, &l->l_dbu);
winner = dmu_buf_set_user(db, &zap->zap_dbu);