linux-kernel - Re: [RFC 2/2] perf/core: change errno for sampling event not supported in hardware

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Message-ID: <20160512064201.GL3192@twins.programming.kicks-ass.net>
Date:	Thu, 12 May 2016 08:42:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	acme@...hat.com, Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	linux-snps-arc@...ts.infradead.org, mingo@...nel.org
Subject: Re: [RFC 2/2] perf/core: change errno for sampling event not
 supported in hardware

On Thu, May 12, 2016 at 11:58:43AM +0530, Vineet Gupta wrote:
> On Thursday 12 May 2016 01:06 AM, Peter Zijlstra wrote:
> > On Mon, May 09, 2016 at 10:53:43PM +0530, Vineet Gupta wrote:
> > 
> >> > Right thats what I feared. But hold on, I don't think we need to change the ABI to
> >> > achieve what we want. Gosh why did I even take that path.
> >> > 
> >> > Currently the errno switch case in perf_evsel__open_strerror() in doesn't handle
> >> > ENOTSUPP. So how about we add that - augmented with the same sample_period !0
> >> > check to barf for lack of sampling support.
> >> > 
> >> > Do you see anything wrong with that ?
> >
> > Should work I think.
> 
> Tried that and doesn't even compile. Reconfirms what Vince said, ENOTSUPP is not
> exposed to userspace (being in include/linux and not include/uapi/linux)

Durr, so what does userspace see?