向事件设置为零的 epoll 添加文件描述符是否有效？

Question

将 epoll_event.events 设置为零的文件描述符添加到 epoll 是否有效？调用 epoll_wait 时预期会发生什么？请参阅简化示例：

struct epoll_event event = {};
event.data.fd = fd;
event.events = 0;

epoll_ctl(efd, EPOLL_CTL_ADD, fd, &event);
epoll_wait(efd, &event, 1, -1);

在此实例中，我可以从 epoll_wait 调用中依赖什么语义？是否有任何事件即使在事件 = 0 时仍会传送？

Answer 1

它应该是有效的，而且 EPOLLERR 和 EPOLLHUP 总是包括在内，即使您没有请求它们，所以设置 events = 0 仍然会响应这两个事件。不过记得检查 epoll_ctl 的 return 值。

文档指出：

The events member is a bit mask composed by ORing together zero or more of the following available event types:

EPOLLERR Error condition happened on the associated file descriptor. This event is also reported for the write end of a pipe when the read end has been closed. epoll_wait(2) will always report for this event; it is not nec‐ essary to set it in events.

EPOLLHUP Hang up happened on the associated file descriptor. epoll_wait(2) will always wait for this event; it is not necessary to set it in events.

向事件设置为零的 epoll 添加文件描述符是否有效？

Is it valid to add a file descriptor to epoll with events set to zero?

c

c++

linux

epoll