Subject: Re: [PATCH net-next 5/5] xdp: get tracepoints xdp_exception and xdp_redirect in sync

From: Daniel Borkmann <[email-masked]>
Date: Wed, 23 Aug 2017 10:54:16 +0200

On 08/23/2017 09:41 AM, Jesper Dangaard Brouer wrote:
> On Tue, 22 Aug 2017 23:30:21 +0200
> Daniel Borkmann <[email-masked]> wrote:
>> On 08/22/2017 10:47 PM, Jesper Dangaard Brouer wrote:
>>> Remove the net_device string name from the xdp_exception tracepoint,
>>> like the xdp_redirect tracepoint.
>>>
>>> Align the TP_STRUCT to have common entries between these two
>>> tracepoint.
>>>
>>> Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
>>> ---
>>>    include/trace/events/xdp.h |   24 ++++++++++++------------
>>>    1 file changed, 12 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
>>> index 7511bed80558..6495b0d9d5c7 100644
>>> --- a/include/trace/events/xdp.h
>>> +++ b/include/trace/events/xdp.h
>>> @@ -31,22 +31,22 @@ TRACE_EVENT(xdp_exception,
>>>    	TP_ARGS(dev, xdp, act),
>>>
>>>    	TP_STRUCT__entry(
>>> -		__string(name, dev->name)
>>>    		__array(u8, prog_tag, 8)
>>>    		__field(u32, act)
>>> +		__field(int, ifindex)
>>>    	),
>>>
>>>    	TP_fast_assign(
>>>    		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
>>>    		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
>>> -		__assign_str(name, dev->name);
>>> -		__entry->act = act;
>>> +		__entry->act		= act;
>>> +		__entry->ifindex	= dev->ifindex;
>>>    	),
>>>
>> [...]
>>>    TRACE_EVENT(xdp_redirect,
>>> @@ -57,26 +57,26 @@ TRACE_EVENT(xdp_redirect,
>>>    	TP_ARGS(from_index, to_index, xdp, act, err),
>>>
>>>    	TP_STRUCT__entry(
>>> -		__field(int, from_index)
>>> -		__field(int, to_index)
>>>    		__array(u8, prog_tag, 8)
>>>    		__field(u32, act)
>>> +		__field(int, from_index)
>>> +		__field(int, to_index)
>>>    		__field(int, err)
>>>    	),
>>>
>>>    	TP_fast_assign(
>>>    		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
>>>    		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
>>> +		__entry->act		= act;
>>>    		__entry->from_index	= from_index;
>>>    		__entry->to_index	= to_index;
>>> -		__entry->act = act;
>>
>> If you already get them in sync, could you also make it consistent
>> that for both tracepoints in TP_ARGS() we use either ifindex
>> directly or device pointer and extract it from TP_fast_assign().
>> Right now, it's mixed.
>
> I did this because, in the (bpf_redirect)_map case, I was hoping that
> "from_index" could be come the index from the map.  Looking closer at
> the devmap design, I cannot see how we can ever know what (the bpf_prog
> thinks) is the corresponding map-ingress/from_index.
>
> Based on that, I think we can/should use the device pointer as arg (as
> you suggested). And then rename "from_index" to "ifindex", where
> ifindex is the XDP ifindex the xdp_buff arrived on.
>
> I guess we can keep the "to_index".  We also need to extend the
> tracepoint args with a "map", to let the trace user tell whether the
> "to_index" is an ifindex or a map-index.

Yeah, makes sense, right now we cannot differentiate between that.

> I'll code this up and submit at V2.

Thanks!