linux内核中sys_poll()的简化分析

app：poll or select;

kernel:
sys_poll();
    do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,struct timespec *end_time);
        poll_initwait(&table);
            init_poll_funcptr(&pwq->pt, __pollwait);>table->qproc =__pollwait;
        do_poll(nfds, head, &table, end_time);
            for (;;) {
                if (do_pollfd(pfd, pt)) { //mask = file->f_op->poll(file, pwait);return mask ----调用驱动中的poll函数                                    
                    count++;//如果驱动的poll函数返回非零，那么count++
                    pt = NULL;
                    }

                //break条件:count非零,超时,有信号等待处理
                if (count || ! timed_out||signal_pending(current))
                    break;

                //休眠__timeout,期间没事发生，则timed_out减为零，再次循环，break
                //休眠期间被中断唤醒等待队列，则再次循环，执行驱动中的poll,返回非零mask, 则break
                __timeout=schedule_timeout(__timeout);
          }