B_WANTED
SET(bp->b_flags, B_WANTED);
CLR(bp->b_flags, B_WANTED);
CLR(bp->b_flags, B_WANTED);
if (ISSET(bp->b_flags, B_WANTED)) {
CLR(bp->b_flags, B_WANTED);
if (ISSET(bp->b_flags, B_WANTED)) {
CLR(bp->b_flags, B_WANTED);
bp->b_flags |= B_WANTED;
bp->b_flags |= B_WANTED;