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

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Message-ID: <20151023145407.GD17308@twins.programming.kicks-ass.net>
Date:	Fri, 23 Oct 2015 16:54:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>, 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 Fri, Oct 23, 2015 at 07:42:22AM -0700, Alexei Starovoitov wrote:
> On 10/23/15 5:03 AM, Peter Zijlstra wrote:
> >So the bpf_perf_event_read() returns the count value, does this not also
> >mean that returning -EINVAL here is also 'wrong'?
> >
> >I mean, sure an actual count value that high is unlikely, but its still
> >a broken interface.
> 
> Agree. that's not pretty interface. I wish I looked at it more carefully
> when it was introduced. Now it's too late to change.

Right; and I figure changing the function signature is not done because
the eBPF stuff is ABI? Unfortunate indeed.
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