B_BUSY
assert(!(bp->b_flags & B_BUSY));
bp->b_flags |= B_BUSY;
bp->b_flags = B_BUSY;
assert(bp->b_flags & B_BUSY);
bp->b_flags &= ~(B_BUSY | B_AGE);
if ((bp->b_flags & (B_BUSY | B_GATHERED)) || !match(fs, bp)) {
(*bpp)->b_flags |= B_BUSY;
(*(sp->bpp))->b_flags |= B_BUSY;
bp->b_flags |= B_BUSY; /* XXX */