linux-kernel - Re: [PATCH] tracing: Kernel access to Ftrace instances

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Message-Id: <20190516120529.4c1f6e6ddd516185df149625@kernel.org>
Date:   Thu, 16 May 2019 12:05:29 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Divya Indi <divya.indi@...cle.com>
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Joe Jin <joe.jin@...cle.com>
Subject: Re: [PATCH] tracing: Kernel access to Ftrace instances

Hi,

On Wed, 15 May 2019 18:51:23 -0700
Divya Indi <divya.indi@...cle.com> wrote:

> Hi Masami,
> 
> Thanks for pointing it out.
> 
> Yes, it should not be static.
> 
> On 5/15/19 5:09 PM, Masami Hiramatsu wrote:
> > HI Divya,
> >
> > On Wed, 20 Mar 2019 11:28:51 -0700
> > Divya Indi <divya.indi@...cle.com> wrote:
> >
> >> Ftrace provides the feature “instances” that provides the capability to
> >> create multiple Ftrace ring buffers. However, currently these buffers
> >> are created/accessed via userspace only. The kernel APIs providing these
> >> features are not exported, hence cannot be used by other kernel
> >> components.
> >>
> >> This patch aims to extend this infrastructure to provide the
> >> flexibility to create/log/remove/ enable-disable existing trace events
> >> to these buffers from within the kernel.
> >>
> >> Signed-off-by: Divya Indi <divya.indi@...cle.com>
> >> Reviewed-by: Joe Jin <joe.jin@...cle.com>
> > Would you tested these APIs with your module? Since,
> > [...]
> >> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> >> index 5b3b0c3..81c038e 100644
> >> --- a/kernel/trace/trace_events.c
> >> +++ b/kernel/trace/trace_events.c
> >> @@ -832,6 +832,7 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
> >>   
> >>   	return ret;
> >>   }
> >> +EXPORT_SYMBOL_GPL(ftrace_set_clr_event);
> > I found this exports a static function to module. Did it work?
> 
> I had tested the changes with my module. This change to static was added 
> in the test patch, but somehow missed it in the final patch that was 
> sent out.

If you can send some example module patch under samples/, that is more
helpful for us to check it. And it is possible to use in kselftest too.

> 
> Will send a new patch along with a few additional ones to add some NULL 
> checks to ensure safe usage by modules and add the APIs to a header file 
> that can be used by the modules.

It seems your's already in Steve's ftrace/core branch, so I think you can make
additional patch to fix it. Steve, is that OK?

Thank you,

> 
> Thanks,
> 
> Divya
> 
> >
> > Thank you,
> >


-- 
Masami Hiramatsu <mhiramat@...nel.org>