linux-kernel - Re: [PATCH v2 0/4] ftrace: important updates

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20090107185349.GC16193@elte.hu>
Date:	Wed, 7 Jan 2009 19:53:49 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Pekka Paalanen <pq@....fi>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Roel Kluin <roel.kluin@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/4] ftrace: important updates


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 7 Jan 2009, Pekka Paalanen wrote:
> 
> > On Wed, 7 Jan 2009 10:49:05 +0100
> > Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > * Steven Rostedt <rostedt@...dmis.org> wrote:
> > > 
> > > >       ring-buffer: rename debugfs file tracing_on to writing_enabled
> > > 
> > > writing_enabled is at least as confusing as tracing_on - if not more so.
> > > 
> > > The user really does not care about all the deeper machinery that happens 
> > > in ftrace - the difference between a 'light' disabling of a tracer and a 
> > > 'heavy' disabling of a tracer (which means it unregisters itself 
> > > completely in essence).
> > > 
> > > To resolve this, we should probably hide this difference altogether (as i 
> > > have suggested to do many months ago, when this first came up), by 
> > > removing tracing_enabled.
> > > 
> > > A tracer can still be fully unregistered: by simply switching the current 
> > > tracer to the 'nop' tracer. tracing_on/off remains the lightweight version 
> > > that most users are interested in anyway.
> > 
> > This sounds even better. We should not need tracing_enabled anymore, since
> > the buffer size can be changed regardless. tracing_on is more useful to
> > mmiotrace than tracing_enabled, too, since mmiotrace does not implement
> > the proper pausing behaviour on the tracing_enabled trigger.
> > 
> > But if Steven wants to keep the "pause" semantics, should there be a
> > callback dispatched to the tracer from tracing_on, just like there is
> > from tracing_enabled currently? Of course the callback semantics would
> > be different and the usual reaction would be to do nothing. It would
> > only be meaningful to tracers that update data outside the ring buffer,
> > so that they can properly pause.
> 
> The tracing_on is implemented by the ring buffer, and disables all ring 
> buffers, even those that are not part of ftrace. This file really has no 
> concept of a tracer. It simply stops writing to the ring buffer.
> 
> Things like the irq latency tracer is will still update its "max time" 
> when tracing is off, although the trace output will not be updated.
> 
> I could remove tracing_enabled, and move the tracing_on to trace.c, that 
> just calls the tracing_off of the ring buffer, and then the file will be 
> at the higher layer, and have a concept of the current tracer.

Sounds good to me. I think the highest utility is in the 'lightweight' 
tracing_on toggle - even though it does not do as thorough of a job of 
disabling a tracer as writing 0 to tracing_on.

I think we shouldnt even _try_ to provide a simple toggle for unregister: 
it is clear from looking at /debug/tracing/current_tracer that the current 
tracer is still active - so asking people to change that back to 'nop' 
will be rather intuitive IMO.

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/