Function vfs_allocate_syncvnode

freebsd/kern/vfs_subr.c:4968–5021

* Create a new filesystem syncer vnode for the specified mount point. */

 * Create a new filesystem syncer vnode for the specified mount point.
 */
void
vfs_allocate_syncvnode(struct mount *mp)
{
	struct vnode *vp;
	struct bufobj *bo;
	static long start, incr, next;
	int error;

	/* Allocate a new vnode */
	error = getnewvnode("syncer", mp, &sync_vnodeops, &vp);
	if (error != 0)
		panic("vfs_allocate_syncvnode: getnewvnode() failed");
	vp->v_type = VNON;
	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
	vp->v_vflag |= VV_FORCEINSMQ;
	error = insmntque(vp, mp);
	if (error != 0)
		panic("vfs_allocate_syncvnode: insmntque() failed");
	vp->v_vflag &= ~VV_FORCEINSMQ;
	VOP_UNLOCK(vp);
	/*
	 * Place the vnode onto the syncer worklist. We attempt to
	 * scatter them about on the list so that they will go off
	 * at evenly distributed times even if all the filesystems
	 * are mounted at once.
	 */
	next += incr;
	if (next == 0 || next > syncer_maxdelay) {
		start /= 2;
		incr /= 2;
		if (start == 0) {
			start = syncer_maxdelay / 2;
			incr = syncer_maxdelay;
		}
		next = start;
	}
	bo = &vp->v_bufobj;
	BO_LOCK(bo);
	vn_syncer_add_to_worklist(bo, syncdelay > 0 ? next % syncdelay : 0);
	/* XXX - vn_syncer_add_to_worklist() also grabs and drops sync_mtx. */
	mtx_lock(&sync_mtx);
	sync_vnode_count++;
	if (mp->mnt_syncer == NULL) {
		mp->mnt_syncer = vp;
		vp = NULL;
	}
	mtx_unlock(&sync_mtx);
	BO_UNLOCK(bo);
	if (vp != NULL) {
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
		vgone(vp);
		vput(vp);
	}
}

void
vfs_deallocate_syncvnode(struct mount *mp)