poll：do_sys_poll---》do_poll---linux-6.0.2\fs\select.c

• static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,struct timespec64 *end_time)
  {
      ......
  	len = min_t(unsigned int, nfds, N_STACK_PPS);
  	for (;;) {
  	.....
          //copy_from_user从用户空间拷贝fds
  		if (copy_from_user(walk->entries, ufds + nfds-todo,
  					sizeof(struct pollfd) * walk->len))
  			goto out_fds;
  	.....
  	}
  	.....
  out_fds:
  	//没有拷贝成功
      .....
  	return err;
  	.....
  }
  

• static int do_poll(struct poll_list *list, struct poll_wqueues *wait,struct timespec64 *end_time)
  {
  	......
      //poll底层处理流程
  	for (;;) {
  		struct poll_list *walk;
  		bool can_busy_loop = false;
  		//这个写法，似乎是链表
  		for (walk = list; walk != NULL; walk = walk->next) {
  			struct pollfd * pfd, * pfd_end;
  
  			pfd = walk->entries;
  			pfd_end = pfd + walk->len;
  			for (; pfd != pfd_end; pfd++) {
  				if (do_pollfd(pfd, pt, &can_busy_loop,
  					      busy_flag)) {
  					count++;
  					pt->_qproc = NULL;
  					/* found something, stop busy polling */
  					busy_flag = 0;
  					can_busy_loop = false;
  				}
  			}
  		}
  		pt->_qproc = NULL;
  		if (!count) {
  			count = wait->error;
  			if (signal_pending(current))
  				count = -ERESTARTNOHAND;
  		}
  		if (count || timed_out)
  			break;
  		if (can_busy_loop && !need_resched()) {
  			if (!busy_start) {
  				busy_start = busy_loop_current_time();
  				continue;
  			}
  			if (!busy_loop_timeout(busy_start))
  				continue;
  		}
  		busy_flag = 0;
  
  		if (end_time && !to) {
  			expire = timespec64_to_ktime(*end_time);
  			to = &expire;
  		}
  
  		if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
  			timed_out = 1;
  	}
  	return count;
  }