From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753857AbbJZMcN (ORCPT <rfc822;w@1wt.eu>);
	Mon, 26 Oct 2015 08:32:13 -0400
Received: from casper.infradead.org ([85.118.1.10]:46640 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753614AbbJZMcM (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 26 Oct 2015 08:32:12 -0400
Date: Mon, 26 Oct 2015 13:32:00 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: Ingo Molnar <mingo@kernel.org>, "David S. Miller" <davem@davemloft.net>,
        Wang Nan <wangnan0@huawei.com>, He Kuang <hekuang@huawei.com>,
        Kaixu Xia <xiakaixu@huawei.com>,
        Daniel Borkmann <daniel@iogearbox.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 net-next] bpf: fix bpf_perf_event_read() helper
Message-ID: <20151026123200.GT2508@worktop.programming.kicks-ass.net>
References: <1445559014-4667-1-git-send-email-ast@kernel.org>
 <20151023120335.GZ17308@twins.programming.kicks-ass.net>
 <562A474E.6040401@plumgrid.com>
 <20151025092142.GB4380@gmail.com>
 <562D0208.7090608@plumgrid.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <562D0208.7090608@plumgrid.com>
User-Agent: Mutt/1.5.22.1 (2013-10-16)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sun, Oct 25, 2015 at 09:23:36AM -0700, Alexei Starovoitov wrote:
> bpf_perf_event_read() muxes of -EINVAL into return value, but it's non
> ambiguous to the program whether it got an error or real counter value.

How can that be, the (u64)-EINVAL value is a valid counter value..
unlikely maybe, but still quite possible.