linux-kernel - Re: Misleading hint to select CONFIG_PERF_EVENTS if driver sets PERF_PMU_CAP_NO

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Date:	Thu, 28 Apr 2016 10:05:13 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Lada Trimasova <Lada.Trimasova@...opsys.com>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>
Subject: Re: Misleading hint to select CONFIG_PERF_EVENTS if driver sets
 PERF_PMU_CAP_NO_INTERRUPT

On Wednesday 27 April 2016 08:43 PM, Lada Trimasova wrote:
> On Tue, 2016-04-26 at 12:42 +0000, Vineet Gupta wrote:
> 
> On Friday 22 April 2016 06:56 PM, Lada Trimasova wrote:
> I think what we have now is sufficient - but u seem to want a prettier failure output.
> 
> Anyhow, this print is coming from util/evsel.c: perf_evsel__open_strerror()
> At the very least you want another entry in switch case for ENOTSUPP and then
> check if event was sampling one (
> evsel->attr.sample_period) - use that as a hint for saying sampling events not
> supported.
> 
> 
> 
> 
> ENOTSUPP is not visible for user programs. So it's impossible to add this entry
> 
> to mentioned switch.
> 
> I think that there is no good way to make error message more understandable
> 
> without breaking existing api.

I meant EOPNOTSUPP. Any errno value has to be visible to user programs otherwise
there is no point defining it.