TDP_BUFNEED
curthread->td_pflags |= TDP_NORUNNINGBUF | TDP_BUFNEED;
(curthread->td_pflags & TDP_BUFNEED) != 0)
(td->td_pflags & TDP_BUFNEED) == 0 &&
norunbuf = ~(TDP_BUFNEED | TDP_NORUNNINGBUF) |
td->td_pflags |= TDP_BUFNEED | TDP_NORUNNINGBUF;