关于rb_buffer_peek()的一个疑问。。。

chishanmingshen

from 3.7.0

1. 
   
2. 
   
3. static struct ring_buffer_event *
   
4. rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
   
5.                unsigned long *lost_events)
   
6. {
   
7.         struct ring_buffer_event *event;
   
8.         struct buffer_page *reader;
   
9.         int nr_loops = 0;
   
10. 
    
11. again:
    
12.         /*
    
13.          * We repeat when a time extend is encountered.
    
14.          * Since the time extend is always attached to a data event,
    
15.          * we should never loop more than once.
    
16.          * (We never hit the following condition more than twice).
    
17.          */
    
18.         if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))<------------------此处是2，老的版本是3！
    
19.                 return NULL;
    
20. 
    
21.         reader = rb_get_reader_page(cpu_buffer);
    
22.         if (!reader)
    
23.                 return NULL;
    
24. 
    
25.         event = rb_reader_event(cpu_buffer);
    
26. 
    
27.         switch (event->type_len) {
    
28.         case RINGBUF_TYPE_PADDING:
    
29.                 if (rb_null_event(event))
    
30.                         RB_WARN_ON(cpu_buffer, 1);
    
31.                 /*
    
32.                  * Because the writer could be discarding every
    
33.                  * event it creates (which would probably be bad)
    
34.                  * if we were to go back to "again" then we may never
    
35.                  * catch up, and will trigger the warn on, or lock
    
36.                  * the box. Return the padding, and we will release
    
37.                  * the current locks, and try again.
    
38.                  */
    
39.                 return event;
    
40. 
    
41.         case RINGBUF_TYPE_TIME_EXTEND:
    
42.                 /* Internal data, OK to advance */
    
43.                 rb_advance_reader(cpu_buffer);
    
44.                 goto again;
    
45. 
    
46.         case RINGBUF_TYPE_TIME_STAMP:
    
47.                 /* FIXME: not implemented */
    
48.                 rb_advance_reader(cpu_buffer);
    
49.                 goto again;
    
50. 
    
51.         case RINGBUF_TYPE_DATA:
    
52.                 if (ts) {
    
53.                         *ts = cpu_buffer->read_stamp + event->time_delta;
    
54.                         ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
    
55.                                                          cpu_buffer->cpu, ts);
    
56.                 }
    
57.                 if (lost_events)
    
58.                         *lost_events = rb_lost_events(cpu_buffer);
    
59.                 return event;
    
60. 
    
61.         default:
    
62.                 BUG();
    
63.         }
    
64. 
    
65.         return NULL;
    
66. }
    
67. 
    

复制代码

版本之间有些差异，奇怪。。。

chishanmingshen

有清楚这个的，请指点一下，谢谢！

灌水菜鸟

兄弟，你试试这个命令呢？
git log Path/File | grep ^commit | cut -d" " -f2 | xargs git show

希望能有用。