epoll源码探秘（epoll_create）

epoll源码探秘（epoll_create）

epoll系列的系统函数，很简单，但是很强大。epoll_create(),epoll_ctl() , epoll_wait()，三个就够了。

一些重要的结构：

/*
 * Each file descriptor added to the eventpoll interface will
 * have an entry of this type linked to the "rbr" RB tree.
 * Avoid increasing the size of this struct, there can be many thousands
 * of these on a server and we do not want this to take another cache line.（红黑树单节点）
 */
struct epitem {
	union {
		/* RB tree node links this structure to the eventpoll RB tree */
		struct rb_node rbn;
		/* Used to free the struct epitem */
		struct rcu_head rcu;
	};

	/* List header used to link this structure to the eventpoll ready list （列表头用于连接结构的eventpoll就绪列表）*/
	struct list_head rdllink;

	/*
	 * Works together "struct eventpoll"->ovflist in keeping the
	 * single linked chain of items.
	 */
	struct epitem *next;

	/* The file descriptor information this item refers to （关联的文件描述符）*/
	struct epoll_filefd ffd;

	/* Number of active wait queue attached to poll operations (轮询操作)*/
	int nwait;

	/* List containing poll wait queues */
	struct list_head pwqlist;

	/* The "container" of this item */
	struct eventpoll *ep;

	/* List header used to link this item to the "struct file" items list */
	struct list_head fllink;