From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 net-next] bpf: fix bpf_perf_event_read() helper
Date: Mon, 26 Oct 2015 13:32:00 +0100
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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
To: Alexei Starovoitov <ast@plumgrid.com>
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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.