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From: Mathieu Desnoyers on 7 May 2010 17:00 * Steven Rostedt (rostedt(a)goodmis.org) wrote: > On Fri, 2010-05-07 at 20:01 +0200, Frederic Weisbecker wrote: > > On Fri, May 07, 2010 at 10:54:38AM -0400, Mathieu Desnoyers wrote: > > > The second is this extra parameter passed whether or not it is needed. > > And although we suppose it is safe, I don't feel comfortable with it. > > So if we can find a more proper way to avoid it, I'm all for it. > > Now I'm making the extra parameter mandatory for all tracepoint > probes. ;-) > > But this time, it will be at the start not the end. > > void probe(void *data, proto); > > > Unfortunately we can't avoid it. In order to remove the extra code > (registering and unregistering) and even share the probe among several > events, we need a way to pass the data to the probe to let the probe > know what event it is dealing with (to put in the event id into the > buffer, to let the tracer output code know what event this data is for). > > The current method is that only the proto that the tracepoint uses is > passed to the probe. This gives us no way to add any more information. > > This new method allows data to be assigned at probe register, and the > probe gets this data as the first parameter. > > The register_* functions will still do typechecking of the probes, they > just add the "void *" at the beginning. > > Actually, here is a place that I can see where Mathieu's check does come > in handy. If we add the check test to each probe, and the tracepoint > proto changes, it will flag it. Ah ! finally we are getting on the same page. :-) > > Mathieu, you've been explaining this wrong ;-) Yep, it seems like I've done a terrible job at trying to explain my motivation to you. ;) > > I'm not worried about changes to ftrace.h breaking things. I'm worried > about changes to tracepoint.h breaking ftrace.h. This is where your > check comes in. As I change the void *data from the end to the start, > I'm nervous about catching all the probes that are registered this way. > (ftrace events, syscalls, kprobes, and perf) I'm nervous about catching all tracepoint-related problems that may arise from both tracepoint and tracepoint probes prototype changes, yes. I'm glad we agree then. :-) Thanks, Mathieu > > -- Steve > > -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |