linux2.6.9 epoll系统调用源码分析

linux2.6.9 epoll系统调用源码分析一、相关的数据结构1、struct eventpollstruct eventpoll {/* Protect the this structure access *//*读写锁*/rwlock_t lock;/** This semaphore is used to ensure that files are not removed* while epoll is using them. This is read-held during the event* collection loop and it is write-held during the file cleanup* path, the epoll file exit code and the ctl operations.*//*读写信号量*/struct rw_semaphore sem;/* Wait queue used by sys_epoll_wait() */wait_queue_head_t wq;/* Wait queue used by file->poll() */wait_queue_head_t poll_wait;/* List of ready file descriptors *//*已完成的操作时间队列*/struct list_head rdllist;/* RB-Tree root used to store monitored fd structs *//*红黑树的跟，保存epoll监视的文件描述符*/struct rb_root rbr;};该结构体用来保存与epoll节点关联的多个文件描述符，保存的方式是使用红黑树实现的hash表。

2、struct ep_pqueue/* Wrapper struct used by poll queueing */struct ep_pqueue {poll_table pt;struct epitem *epi;};这个结构体类似于select/poll中的struct poll_wqueues。

由于epoll需要在内核态保存大量信息，所以光光一个回调函数指针已经不能满足要求，所以在这里引入了一个新的结构体struct epitem。

3、struct epoll_eventstruct epoll_event {__u32events;__u64data;} EPOLL_PACKED;4、struct epitem/** Each file descriptor added to the eventpoll interface will* have an entry of this type linked to the hash.*/struct epitem {/* RB-Tree node used to link this structure to the eventpoll rb-tree *//*红黑树节点，将本节点挂载到eventpoll 所对应的红黑树*/ struct rb_node rbn;/* List header used to link this structure to the eventpoll ready list *//*双向链表，用来将该节点链接到已完成队列上*/struct list_head rdllink;/* The file descriptor information this item refers to *//*这个结构体对应被监听的文件描叙符信息*/struct epoll_filefd ffd;/* Number of active wait queue attached to poll operations *//*poll操作中事件的个数*/int nwait;/* List containing poll wait queues *//*双向链表，保存着被监视文件的等待队列，功能*//*类似于select/poll中的poll_table*/struct list_head pwqlist;/* The "container" of this item *//*指向eventpoll，多个epitem对应一个eventpoll*/struct eventpoll *ep;/* The structure that describe the interested events and the source fd *//*记录发生的时间和对应fd*/struct epoll_event event;/** Used to keep track of the usage count of the structure. This avoids* that the structure will desappear from underneath our processing.*//*引用计数*/atomic_t usecnt;/* List header used to link this item to the "struct file" items list *//*双向链表，用来链接被监视的文件描述符对应的struct file。

因为file 里有f_ep_link，用来保存所有监视这个文件的epoll节点*/struct list_head fllink;/* List header used to link the item to the transfer list *//*双向链表，用来保存传输队列*/struct list_head txlink;/** This is used during the collection/transfer of events to userspace* to pin items empty events set.*//*文件描述符的状态，在收集和传输时用来锁住空的事件集合*/unsigned int revents;};5、eppoll_entry/* Wait structure used by the poll hooks */struct eppoll_entry {/* List header used to link this structure to the "struct epitem" */struct list_head llink;/* The "base" pointer is set to the container "struct epitem" */void *base;/** Wait queue item that will be linked to the target file wait* queue head.*/wait_queue_t wait;/* The wait queue head that linked the "wait" wait queue item */wait_queue_head_t *whead;};6、epoll_filefdstruct epoll_filefd {struct file *file;int fd;};二、源码分析1、eventpoll_init函数源码static int__init eventpoll_init(void){int error;init_MUTEX(&epsem);/* Initialize the structure used to perform safe poll wait head wake ups */ep_poll_safewake_init(&psw);/* Allocates slab cache used to allocate "struct epitem" items */epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC,NULL, NULL);/* Allocates slab cache used to allocate "struct eppoll_entry" */pwq_cache = kmem_cache_create("eventpoll_pwq",sizeof(struct eppoll_entry), 0,EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL);/** Register the virtual file system that will be the source of inodes* for the eventpoll files*//*注册了一个新的文件系统，叫"eventpollfs"（在eventpoll_fs_type结构里），然后挂载此文件系统*/error = register_filesystem(&eventpoll_fs_type);if (error)goto epanic;/* Mount the above commented virtual file system */eventpoll_mnt = kern_mount(&eventpoll_fs_type);error = PTR_ERR(eventpoll_mnt);if (IS_ERR(eventpoll_mnt))goto epanic;DNPRINTK(3, (KERN_INFO"[%p] eventpoll: successfully initialized.\n",current));return 0;epanic:panic("eventpoll_init() failed\n");}epoll是个module，所以先看看module的入口eventpoll_init。

这个module在初始化时注册了一个新的文件系统，叫"eventpollfs"（在eventpoll_fs_type结构里），然后挂载此文件系统。