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Subject: Re: [PATCH v9 3.2 0/9] Uprobes patchset with perf probe support
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
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        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Anton Arapov <anton@redhat.com>,
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Date: Wed, 25 Jan 2012 15:11:27 +0100
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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.