netdev - Re: HW communication debugging interface

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Date:	Mon, 05 Oct 2015 08:47:09 -0700
From:	John Fastabend <john.fastabend@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
CC:	Andrew Lunn <andrew@...n.ch>, "Rosen, Rami" <rami.rosen@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"eladr@...lanox.com" <eladr@...lanox.com>,
	"idosch@...lanox.com" <idosch@...lanox.com>
Subject: Re: HW communication debugging interface - ideas?

On 15-10-05 08:35 AM, Jiri Pirko wrote:
> Mon, Oct 05, 2015 at 05:29:09PM CEST, john.fastabend@...il.com wrote:
>> On 15-10-05 08:18 AM, Jiri Pirko wrote:
>>> Mon, Oct 05, 2015 at 04:58:42PM CEST, andrew@...n.ch wrote:
>>>> On Mon, Oct 05, 2015 at 04:55:42PM +0200, Jiri Pirko wrote:
>>>>> Mon, Oct 05, 2015 at 04:49:41PM CEST, andrew@...n.ch wrote:
>>>>>>>> Are you referring here to messages of the EMAD protocol ?
>>>>>>
>>>>>> I know nothing about this protocol.....
>>>>>>
>>>>>> Does it at least use standard Ethernet framing? Source and Destination
>>>>>> header and an EtherType which mean EMAD?
>>>>>
>>>>> Yep, but that does not really matter. I believe we should find debugging
>>>>> interface which is protocol agnostic. Just arbitrary messages
>>>>> monitoring.
>>>>
>>>> Hi Jiri
>>>>
>>>> O.K, it is just that you mentioned wireshark. Passing the frames to
>>>> network interface taps would make this trivial.
>>>
>>> That is true. But using netlink+nlmon would do the same.
>>
>> Also I guess if you go this direction you want to make it generic
>> enough for any drivers to use it to snoop software/firmware msgs. This
>> is common across many devices.
> 
> Yes, definitelly, this should be something generic to be usable for
> every device type.
> 
> 
>>
>> In the past though I've just used ethtool dump commands and some
>> "scripts" on top of this to debug devices. And when it got really
>> bad wrote some throw away code to debug my issue. I guess it might
>> be nice to have something in the kernel to improve this but have
>> you considered using the tracing features that already exist?
> 
> Which ones do you have in mind?
> 

I was thinking something like kprobes+bpf to dump a trace and
then a lua script in wireshark to parse the input and pretty
print it for users. This might get you good-enough support without
having to carry it around in the kernel just so we can debug
the devices. We could build some libs/pkgs around it in userspace
and get it published somewhere so we can all work on it together.

I suspect the primary users for this will be developers anyways
and maybe some users who have a real nasty bug.

> 
>>
>> .John
>>
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