linux-kernel - Re: [PATCH] usb: gadget: functions: add ftrace export over USB

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Message-ID: <87fudz5x1j.fsf@linux.intel.com>
Date:   Fri, 14 Jul 2017 09:53:44 +0300
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Pratyush Anand <panand@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Linux USB <linux-usb@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Chunyan Zhang <zhang.chunyan@...aro.org>
Subject: Re: [PATCH] usb: gadget: functions: add ftrace export over USB


Hi,

Pratyush Anand <panand@...hat.com> writes:
> On Friday 09 June 2017 03:58 PM, Felipe Balbi wrote:
>> Felipe Balbi <felipe.balbi@...ux.intel.com> writes:
>>
>>> Allow for ftrace data to be exported over a USB Gadget
>>> Controller. With this, we have a potentially very fast pipe for
>>> transmitting ftrace data to a Host PC for further analysis.
>>>
>>> Note that in order to decode the data, one needs access to kernel
>>> symbols in order to convert binary data into function names and what
>>> not.
>>>
>>> Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
>>> ---
>>>
>>> I wanted to take this through the gadget tree, but there is a
>>> dependency with a previous patch of mine adding and extra argument to
>>> the ->write() function. Hoping someone else will take it.
>>
>> just as an extra note here. In order for this to be really useful, it
>> would be nice to be able to control what is going to be traced over USB
>
> Probably you will also need to export *atleast* symbol information. In future, 

just keep your vmlinux around. This is not supposed to be shipped on end
products, only debug builds.

> if this framework is extended to export tracepoint/kprobe/uprobe event data, 
> then the information like event format etc will also need to be exported.
>
> What tool do you use on host machine in order to extract information from this 
> exported target ring buffer data?
> IMHO, standard tools like trace-cmd will not be able to use it as it is.

I hacked something together with libusb for testing. Proper tooling is
needed, indeed.

-- 
balbi

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