linux-kernel - Re: [PATCH v9 3.2 0/9] Uprobes patchset with perf probe support

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Message-ID: <1327500687.2614.70.camel@laptop>
Date:	Wed, 25 Jan 2012 15:11:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v9 3.2 0/9] Uprobes patchset with perf probe support

On Tue, 2012-01-17 at 10:39 +0100, Ingo Molnar wrote:

> I did not suggest anything complex or intrusive: just basically 
> unify the namespace, have a single set of callbacks, and call 
> into the uprobes and perf code from those callbacks - out of the 
> sight of MM code.
> 
> That unified namespace could be called:
> 
>     event_mmap(...);
>     event_fork(...);
> 
> etc. - and from event_mmap() you could do a simple:
> 
> 	perf_event_mmap(...)
> 	uprobes_event_mmap(...)
> 
> [ Once all this is updated to use tracepoints it would turn into 
>   a notification callback chain kind of thing. ]

We keep disagreeing on this. I utterly loathe hiding stuff in notifier
lists. It makes it completely non-obvious who all does what.

Another very good reason to not do what you suggest is that
perf_event_mmap() is a pure consumer, it doesn't have a return value,
whereas uprobes_mmap() can actually fail the mmap.



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