vcap_chain_offset
diff = vcap_chain_offset(vctrl, f->common.chain_index, to_cid);
diff = vcap_chain_offset(vctrl, from_cid, to_cid);
EXPORT_SYMBOL_GPL(vcap_chain_offset);
int vcap_chain_offset(struct vcap_control *vctrl, int from_cid, int to_cid);