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Is there any way to filter out trace-cmd report based on network interface name (Eg: eth1 or eth2) ?
When i try to use "name" as EVENT_FIELD in trace-cmd report filter i get nothing.
Following is the command i used

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

But i was able to use "len" as 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

Following is the event format for netif_receive_skb

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

And in trace-cmd-report i found following details 

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.

So in short i want to know command to filter out based on "name" EVENT_FIELD

Thanks in advance,
prap4search

prap4search
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1 Answers1

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This is indeed a bug in trace-cmd .
I got following patch from Steven Rostedt(creator of trace-cmd) as a fix.

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 */

After applying patch i can filter out using interface name

[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
prap4search
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