Man page 9 : skb_complete_tx_timestamp

skb_complete_tx_timestamp - deliver cloned skb with tx timestamps

void skb_complete_tx_timestamp(struct sk_buff *  skb , struct skb_shared_hwtstamps *  hwtstamps );

skb
    clone of the the original outgoing packet

hwtstamps
    hardware time stamps, may be NULL if not available

PHY drivers may accept clones of transmitted packets for timestamping via their phy_driver.txtstamp method. These drivers must call this function to return the skb back to the stack, with or without a timestamp.