Function ng_upgrade_write

lib/ff_ng_base.c:2097–2160

#if 0
static __inline item_p
ng_upgrade_write(node_p node, item_p item)
{
    struct ng_queue *ngq = &node->nd_input_queue;
    KASSERT(node != &ng_deadnode,
        ("%s: working on deadnode", __func__));

    NGI_SET_WRITER(item);

    NG_QUEUE_LOCK(ngq);

    /*
     * There will never be no readers as we are there ourselves.
     * Set the WRITER_ACTIVE flags ASAP to block out fast track readers.
     * The caller we are running from will call ng_leave_read()
     * soon, so we must account for that. We must leave again with the
     * READER lock. If we find other readers, then
     * queue the request for later. However "later" may be rignt now
     * if there are no readers. We don't really care if there are queued
     * items as we will bypass them anyhow.
     */
    atomic_add_int(&ngq->q_flags, WRITER_ACTIVE - READER_INCREMENT);
    if ((ngq->q_flags & (NGQ_WMASK & ~OP_PENDING)) == WRITER_ACTIVE) {
        NG_QUEUE_UNLOCK(ngq);
        
        /* It's just us, act on the item. */
        /* will NOT drop writer lock when done */
        ng_apply_item(node, item, 0);

        /*
         * Having acted on the item, atomically
         * downgrade back to READER and finish up.
          */
        atomic_add_int(&ngq->q_flags, READER_INCREMENT - WRITER_ACTIVE);

        /* Our caller will call ng_leave_read() */
        return;
    }
    /*
     * It's not just us active, so queue us AT THE HEAD.
     * "Why?" I hear you ask.
     * Put us at the head of the queue as we've already been
     * through it once. If there is nothing else waiting,
     * set the correct flags.
     */
    if (STAILQ_EMPTY(&ngq->queue)) {
        /* We've gone from, 0 to 1 item in the queue */
        atomic_set_int(&ngq->q_flags, OP_PENDING);

        CTR3(KTR_NET, "%20s: node [%x] (%p) set OP_PENDING", __func__,
            node->nd_ID, node);
    };
    STAILQ_INSERT_HEAD(&ngq->queue, item, el_next);
    CTR4(KTR_NET, "%20s: node [%x] (%p) requeued item %p as WRITER",
        __func__, node->nd_ID, node, item );

    /* Reverse what we did above. That downgrades us back to reader */
    atomic_add_int(&ngq->q_flags, READER_INCREMENT - WRITER_ACTIVE);