Date: Wed, 26 Jun 2013 10:12:23 +0200
From: Robert Richter <rric@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Jiri Olsa <jolsa@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 00/14] perf, persistent: Kernel updates for perf tool
 integration
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On 25.06.13 21:16:54, Borislav Petkov wrote:
> On Tue, Jun 25, 2013 at 07:57:29PM +0200, Robert Richter wrote:
> > But what options there are to detach the event from all processes and
> > make it persistent?
> 
> Something like this:
> 
> 	ioctl(fd, PERF_EVENT_IOC_DETACH, 0);
> 
> I guess this could simply set the persistent flag so that the rest of
> the perf code knows not to destroy event buffers etc.
> 
> I don't have an idea about the reattaching though because you don't have
> a file descriptor there.
> 
> Maybe for that we could really use the sys_perf_event_open() with flags
> set to PERF_FLAG_PERSISTENT to note that we want to reattach to the
> persistent event instead of opening a new one.

We get a new fd by opening the persistent event with the syscall.
There would be 2 new ioctls:

 ioctl(fd, PERF_EVENT_IOC_DETACH, 0);
 ioctl(fd, PERF_EVENT_IOC_ATTACH, 0);

This would be fine and reuses existing infrastructure.

-Robert
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