Re: [rfc] Describe events in a structured way via sysfs

[Ingo Molnar <mingo@elte.hu>]

* Johannes Berg <johannes@sipsolutions.net> wrote:

> On Tue, 2010-06-22 at 15:22 +0800, Lin Ming wrote:
> 
> > > > net/wlan0/events/
> > > > net/waln1/events/
> > > > ....
> > > > net/walnN/events/
> > > 
> > > That's not appropriate either though since you may have multiple network 
> > > interfaces on the same hardware :)
> > 
> > Doesn't net/wlan0...wlanN mean multiple network interfaces on the same 
> > hardware?
> 
> Yes, but the trace points aren't per network interface but rather per 
> hardware piece.

Yeah - we generally want events to live at their 'natural' source in sysfs.

So if it's a per device hardware event, it should live with the hardware 
piece. If it's a higher level chipset event, it should live where the chipset 
driver is in sysfs. If it's a subsystem level event then it should live there.

I think what you mentioned in your other posting makes the most sense: give 
flexibility to tracepoint authors to place the event in the most sensible 
sysfs place. It is them who define the tracepoints and the events so any 
second guessing by a generic layer will probably get in the way. The generic 
tool layer will be content with having the event_source class in sysfs, to see 
'all' event sources ttheir topological structure.

That's probably best achieved via a TRACE_EVENT() variant, by passing in the 
sysfs location.

It might even make sense to make this a part of TRACE_EVENT() itself and make 
'NULL' the current default, non-sysfs-enumerated behavior. That way we can 
gradually (and non-intrusively) find all the right sysfs places for events.

Thanks,

	Ingo