printk 的问题

shi_wen_qiang

下面的文字是 LDD3 里面的：

If the circular buffer fills up, printk wraps around and starts adding new data to the beginning of the buffer, overwriting the oldest data. Therefore, the logging process loses the oldest data. This problem is negligible compared with the advantages of using such a circular buffer. For example, a circular buffer allows the system to run even without a logging process, while minimizing memory waste by overwriting old data should nobody read it. Another feature of the Linux approach to messaging is that printk can be invoked from anywhere, even from an interrupt handler, with no limit on how much data can be printed. The only disadvantage is the possibility of losing some data.

(1) even from an interrupt handler
-------------------------------------------
      这句话的意思就是：
      
      interrupt handler 里面一般都会上锁(spinlock)，那就是说即使在上锁(spinlock)后，printk 也是可以使用的？

(2) The only disadvantage is the possibility of losing some data
--------------------------------------------
这句话的意思不太明白，麻烦大家指点下. tks.

shi_wen_qiang

哦，关于第 (2) 个问题应该是这样的：

printk 因为会把信息 print 到 kernel 的“环回 buffer"，这样的缺点便是可能导致 log 信息的丢失.

dreamice

回复 2# shi_wen_qiang


    是的，printk的信息有可能会丢失的

shi_wen_qiang

谢谢大家. 但是 ‘第一个’ 问题还没人给予回答，请大家多多指点.

garyv

回复 4# shi_wen_qiang


    这几句话里面没有提到自旋锁啊，提到了printk可以用于任何上下文包括中断上下文。