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

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Date:   Fri, 14 Jul 2017 17:44:25 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Pratyush Anand <panand@...hat.com>
Cc:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        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

On Fri, 14 Jul 2017 11:22:51 +0530
Pratyush Anand <panand@...hat.com> wrote:

> Hi Felipe,
> 
> 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, 
> 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.
>

Have you looked at how trace-cmd does network transfers? Perhaps this
can do something similar. I'm also working on having trace-cmd work
through sockets for guest to host tracing.

See trace-cmd listen.

-- Steve