Function flushbufqueues

freebsd/kern/vfs_bio.c:3473–3605

    "Number of buffers flushed with dependecies that require rollbacks");

static int
flushbufqueues(struct vnode *lvp, struct bufdomain *bd, int target,
    int flushdeps)
{
	struct bufqueue *bq;
	struct buf *sentinel;
	struct vnode *vp;
	struct mount *mp;
	struct buf *bp;
	int hasdeps;
	int flushed;
	int error;
	bool unlock;

	flushed = 0;
	bq = &bd->bd_dirtyq;
	bp = NULL;
	sentinel = malloc(sizeof(struct buf), M_TEMP, M_WAITOK | M_ZERO);
	sentinel->b_qindex = QUEUE_SENTINEL;
	BQ_LOCK(bq);
	TAILQ_INSERT_HEAD(&bq->bq_queue, sentinel, b_freelist);
	BQ_UNLOCK(bq);
	while (flushed != target) {
		maybe_yield();
		BQ_LOCK(bq);
		bp = TAILQ_NEXT(sentinel, b_freelist);
		if (bp != NULL) {
			TAILQ_REMOVE(&bq->bq_queue, sentinel, b_freelist);
			TAILQ_INSERT_AFTER(&bq->bq_queue, bp, sentinel,
			    b_freelist);
		} else {
			BQ_UNLOCK(bq);
			break;
		}
		/*
		 * Skip sentinels inserted by other invocations of the
		 * flushbufqueues(), taking care to not reorder them.
		 *
		 * Only flush the buffers that belong to the
		 * vnode locked by the curthread.
		 */
		if (bp->b_qindex == QUEUE_SENTINEL || (lvp != NULL &&
		    bp->b_vp != lvp)) {
			BQ_UNLOCK(bq);
			continue;
		}
		error = BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL);
		BQ_UNLOCK(bq);
		if (error != 0)
			continue;

		/*
		 * BKGRDINPROG can only be set with the buf and bufobj
		 * locks both held.  We tolerate a race to clear it here.
		 */
		if ((bp->b_vflags & BV_BKGRDINPROG) != 0 ||
		    (bp->b_flags & B_DELWRI) == 0) {
			BUF_UNLOCK(bp);