VFS_SYNC
VFS_SYNC(mp, MNT_NOWAIT | MNT_LAZY);
error = VFS_SYNC(mp, MNT_WAIT);
VFS_SYNC(mp, MNT_NOWAIT);
VFS_SYNC(mp, MNT_WAIT);
error = VFS_SYNC(mp, MNT_WAIT);
(error = VFS_SYNC(vp->v_rdev->si_mountpoint, MNT_WAIT)) != 0)
VFS_SYNC(mp, MNT_WAIT);