linux - 如何根据网络接口(interface)名称获取 trace-cmd 报告(例如 : eth2)?

Question

有什么方法可以根据网络接口(interface)名称(例如:eth1 或 eth2)过滤掉 trace-cmd 报告？
当我尝试在 trace-cmd 报告过滤器中使用“名称”作为 EVENT_FIELD 时，我什么也没得到。
以下是我使用的命令

  [prap4test]$trace-cmd report -F 'net/netif_receive_skb:name=="eth1"'
  version = 6
  cpus=2
  [prap4test]$

但我能够使用“len”作为 EVENT_FIELD

[prap4test]$trace-cmd report -F 'net/netif_receive_skb'
version = 6
cpus=2
       trace-cmd-19979 [000] 499726.602505: netif_receive_skb:    dev=eth2 skbaddr=0xffff8800e9bb0e00 len=84
            sshd-21184 [000] 499726.603209: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e9bb0f00 len=52
       trace-cmd-19978 [000] 499727.809932: netif_receive_skb:    dev=eth2 skbaddr=0xffff8800e9bb5000 len=46
       trace-cmd-19979 [001] 499728.105372: netif_receive_skb:    dev=eth2 skbaddr=0xffff8800e753cc00 len=328
       trace-cmd-19978 [000] 499728.780571: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e9bb0700 len=100
[prap4test]$trace-cmd report -F 'net/netif_receive_skb:len >= 50'
version = 6
cpus=2
       trace-cmd-19979 [000] 499726.602505: netif_receive_skb:    dev=eth2 skbaddr=0xffff8800e9bb0e00 len=84
            sshd-21184 [000] 499726.603209: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e9bb0f00 len=52
       trace-cmd-19979 [001] 499728.105372: netif_receive_skb:    dev=eth2 skbaddr=0xffff8800e753cc00 len=328
       trace-cmd-19978 [000] 499728.780571: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e9bb0700 len=100

netif_receive_skb的事件格式如下

name: netif_receive_skb
ID: 991
format:
        field:unsigned short common_type;       offset:0;       size:2; signed:0;
        field:unsigned char common_flags;       offset:2;       size:1; signed:0;
        field:unsigned char common_preempt_count;       offset:3;       size:1; signed:0;
        field:int common_pid;   offset:4;       size:4; signed:1;

        field:void * skbaddr;   offset:8;       size:8; signed:0;
        field:unsigned int len; offset:16;      size:4; signed:0;
        field:__data_loc char[] name;   offset:20;      size:4; signed:1;

print fmt: "dev=%s skbaddr=%p len=%u", __get_str(name), REC->skbaddr, REC->len

在 trace-cmd-report 中我发现了以下细节

Note, the EVENT_FIELD is the field name as shown by an events format
(as displayed with *--events*), and not what is found in the output.
If the output shows "ID:foo" but the field that "foo" belongs to was
called "name" in the event format, then "name" must be used in the filter.
The same is true about values. If the value that is displayed is converted
by to a string symbol, the filter checks the original value and not the
value displayed. For example, to filter on all tasks that were in the
running state at a context switch:

    -F 'sched/sched_switch : prev_state==0'

Although the output displays 'R', having 'prev_stat=="R"' will not work.

简而言之，我想知道根据“名称”EVENT_FIELD 过滤掉的命令

提前致谢，
prap4search

Answer 1

这确实是 trace-cmd 中的一个错误。
我从 Steven Rostedt(trace-cmd 的创建者)那里获得了以下补丁作为修复。

diff --git a/parse-filter.c b/parse-filter.c
index c2fd26f..8e302c4 100644
--- a/parse-filter.c
+++ b/parse-filter.c
@@ -1880,17 +1880,25 @@ static const char *get_field_str(struct filter_arg *arg, struct pevent_record *r
    struct pevent *pevent;
    unsigned long long addr;
    const char *val = NULL;
+    unsigned int size;
    char hex[64];

    /* If the field is not a string convert it */
    if (arg->str.field->flags & FIELD_IS_STRING) {
        val = record->data + arg->str.field->offset;
+        size = arg->str.field->size;
+
+        if (arg->str.field->flags & FIELD_IS_DYNAMIC) {
+            addr = *(unsigned int *)val;
+            val = record->data + (addr & 0xffff);
+            size = addr >> 16;
+        }

        /*
        * We need to copy the data since we can't be sure the field
        * is null terminated.
        */
-        if (*(val + arg->str.field->size - 1)) {
+        if (*(val + size - 1)) {
            /* copy it */
            memcpy(arg->str.buffer, val, arg->str.field->size);
            /* the buffer is already NULL terminated */

应用补丁后，我可以使用接口(interface)名称过滤掉

[prap4test]$../trace-cmd/trace-cmd report -F 'net/netif_receive_skb:name=="eth1"'
cpus=2
       trace-cmd-1108  [000] 1111798.397704: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e9f5ee00 len=52
       trace-cmd-1108  [000] 1111798.428998: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e867b400 len=392
       trace-cmd-1108  [000] 1111798.989447: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e743ed00 len=46
       trace-cmd-1108  [000] 1111799.450838: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800eab94b00 len=576
       trace-cmd-1108  [000] 1111799.549737: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800eab94700 len=576
       trace-cmd-1108  [000] 1111800.263439: netif_receive_skb:    dev=eth1 skbaddr=0xffff8800e87c4e00 len=100