netdev - Re: [PATCH v3 net-next] bpf: fix bpf_perf_event

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Message-ID: <20151026123200.GT2508@worktop.programming.kicks-ass.net>
Date:	Mon, 26 Oct 2015 13:32:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Wang Nan <wangnan0@...wei.com>, He Kuang <hekuang@...wei.com>,
	Kaixu Xia <xiakaixu@...wei.com>,
	Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next] bpf: fix bpf_perf_event_read() helper

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.
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