BC_WANTED
obp->b_cflags &= ~(BC_BUSY | BC_WANTED);
if (ISSET(bp->b_cflags, BC_WANTED))
CLR(bp->b_cflags, BC_WANTED|BC_AGE);
KASSERT((bp->b_cflags & BC_WANTED) == 0);
bp->b_cflags |= BC_WANTED;
bp->b_cflags |= BC_WANTED;
if (unbusybp->b_cflags & BC_WANTED)