----- Original Message ----- > From: "Steven Rostedt" <[email protected]> > To: "Mathieu Desnoyers" <[email protected]> > Cc: "Frank Ch. Eigler" <[email protected]>, [email protected], "Ingo > Molnar" <[email protected]>, "Frederic > Weisbecker" <[email protected]>, "Andrew Morton" > <[email protected]>, "Johannes Berg" > <[email protected]>, "Linus Torvalds" <[email protected]>, > "Peter Zijlstra" > <[email protected]>, "Thomas Gleixner" <[email protected]>, "Greg > Kroah-Hartman" <[email protected]>, > "lttng-dev" <[email protected]>, "Rusty Russell" > <[email protected]> > Sent: Wednesday, March 12, 2014 11:46:11 AM > Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set > via debugfs > > > To sum up this thread, and get the signal vs noise ratio up. > > On Wed, 12 Mar 2014 11:11:00 -0400 > Steven Rostedt <[email protected]> wrote: > > > > The solution I like the most that I believe will work for both of us, > > is to to move this magic "enable tracepoint in the future" to your > > LTTng module. Have your module register a module load and unload handler > > to be able to see the tracepoints that exist in the module, and you can > > enable them then. When a module is unloaded, your module can do the > > accounting to record that, and the state of its tracepoints. > > This is my final proposal. > > I'll add the patch that removes the tracepoint on failure along with > returning -ENODEV. That way, there will be no registered tracepoints > that do not exist. > > I'll also make sure that on module unload, the tracepoints are disabled > for the module as well.
Do you mean that the tracepoint probe will be unregistered from within tracepoint.c whenever all modules containing tracepoint call sites are unloaded ? If so, how do you plan to handle ownership of the "name", "probe" and "data" pointer ? They belong to the tracer. Would they simply leak ? > > Then, you can simply add a module notifier that does the work that you > like, and save and restore the state of named tracepoints and enabled > them on module load. Just set the priority of the notifier to 1 > so that it runs after the tracepoint notifier that adds the new > tracepoints to the system. I don't mind the extra work on the LTTng side at all. What I am concerned about are changes that would make the tracepoint API sloppy. > > > > > Looks like we can have it both ways. A way that works well for the > > kernel, and a way that works well for you. But your module will need to > > do the heavy work for what you want. > > > > To me, a tracepoint should only be enabled when it exists. If it is > > enabled in module when the module is unloaded, then it should be > > removed after the module has left. If the module is loaded again, it is > > up to the user (or your module) to enable that tracepoint again. > > I want to point out that LTTng should not be dictating the way the > kernel works, but it should be the other way around. I don't care about doing extra work in LTTng, no worries about that. I'm just trying to ensure all the corner cases are thought through when a change such as this is proposed in a core infrastructure like tracepoints. Thanks, Mathieu > > -- Steve > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
