tcp_retransmit_skb的kprobe而不是tcp_retransmit_skb @tcp_states，我想kprobe __napi_schedule

问题描述

在BPF Performance Tools一书中，有tcp_retransmit_skb的kprobe实现。我想做同样的事情，而不是tcp_retransmit_skb @tcp_states，我想kprobe _ napi_schedule并包含'include / linux / netdevice.h'的枚举NAPI_STATE *。以上是我的实现：

 1 #!/usr/local/bin/bpftrace
  2
  3 #include <linux/netdevice.h>
  4
  5 kprobe:__napi_schedule
  6 {
  7         $ns = (struct napi_struct *)arg0;
  8
  9         // Poll is scheduled
 10         @napi[1] = "NAPI_STATE_SCHED";
 11         @napi[2] = "NAPI_STATE_disABLE";
 12         @napi[3] = "NAPI_STATE_NPSVC";
 13         @napi[4] = "NAPI_STATE_HASHED";
 14         @napi[5] = "NAPI_STATE_NO_BUSY_POLL";
 15
 16
 17         printf("-------------------\n");
 18         printf("\n");
 19         printf("__napi_schedule: %s pid: %d\n",comm,pid);
 20         printf("\n");
 21         $state = $ns->state;
 22         printf("$ns->state: %d\n",$state);
 23         $statestr = @napi[$state];
 24         printf("state is: %s\n",$statestr);
 25         clear(@napi);
 26         printf("--------------------\n");
 27 }

当我尝试运行它时，它在我的printf中没有显示“状态为”。

输出为：

...
__napi_schedule: tmux: server pid: 9003

$ns->state: 17
state is:
--------------------
-------------------

__napi_schedule: tmux: server pid: 9003

$ns->state: 17
state is:
--------------------
-------------------

__napi_schedule: tmux: server pid: 9003

$ns->state: 17
state is:
--------------------
...

解决方法

$ns->state是一个位数组，因此值17实际上是(1 << NAPI_STATE_SCHED) | (1 << NAPI_STATE_HASHED)。

您将需要遍历位以解析值并显示等效的字符串。