Function ktr_drain

freebsd/kern/kern_ktrace.c:362–384

* Drain any pending ktrace records from the per-thread queue to disk. This * is used both internally before committing other records, and also on * system call return. We drain all the ones we can find at the time when * drain is requested, but don't keep draining after that as those events * may be approximately "after" the current event. */

 * may be approximately "after" the current event.
 */
static void
ktr_drain(struct thread *td)
{
	struct ktr_request *queued_req;
	STAILQ_HEAD(, ktr_request) local_queue;

	ktrace_assert(td);
	sx_assert(&ktrace_sx, SX_XLOCKED);

	STAILQ_INIT(&local_queue);

	if (!STAILQ_EMPTY(&td->td_proc->p_ktr)) {
		mtx_lock(&ktrace_mtx);
		STAILQ_CONCAT(&local_queue, &td->td_proc->p_ktr);
		mtx_unlock(&ktrace_mtx);

		while ((queued_req = STAILQ_FIRST(&local_queue))) {
			STAILQ_REMOVE_HEAD(&local_queue, ktr_list);
			ktr_writerequest(td, queued_req);
			ktr_freerequest(queued_req);
		}
	}
}

/*
 * Submit a trace record for immediate commit to disk -- to be used only