libevent源码分析：bufferevent

struct bufferevent定义在文件bufferevent_struct.h中。

 1 /**
 2   Shared implementation of a bufferevent.
 3
 4   This type is exposed only because it was exposed in previous versions,
 5   and some people‘s code may rely on manipulating it.  Otherwise, you
 6   should really not rely on the layout, size, or contents of this structure:
 7   it is fairly volatile, and WILL change in future versions of the code.
 8 **/
 9 struct bufferevent {
10     /** Event base for which this bufferevent was created. */
11     struct event_base *ev_base;
12     /** Pointer to a table of function pointers to set up how this
13         bufferevent behaves. */
14     const struct bufferevent_ops *be_ops;
15
16     /** A read event that triggers when a timeout has happened or a socket
17         is ready to read data.  Only used by some subtypes of
18         bufferevent. */
19     struct event ev_read;
20     /** A write event that triggers when a timeout has happened or a socket
21         is ready to write data.  Only used by some subtypes of
22         bufferevent. */
23     struct event ev_write;
24
25     /** An input buffer. Only the bufferevent is allowed to add data to
26         this buffer, though the user is allowed to drain it. */
27     struct evbuffer *input;
28
29     /** An input buffer. Only the bufferevent is allowed to drain data
30         from this buffer, though the user is allowed to add it. */
31     struct evbuffer *output;
32
33     struct event_watermark wm_read;
34     struct event_watermark wm_write;
35
36     bufferevent_data_cb readcb;
37     bufferevent_data_cb writecb;
38     /* This should be called ‘eventcb‘, but renaming it would break
39      * backward compatibility */
40     bufferevent_event_cb errorcb;
41     void *cbarg;
42
43     struct timeval timeout_read;
44     struct timeval timeout_write;
45
46     /** Events that are currently enabled: currently EV_READ and EV_WRITE
47         are supported. */
48     short enabled;
49 };