netdev - Re: [PATCH/RFC] Make perf_event_open() propagate errors for use in bpf_perf_event

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Message-ID: <20190118145237.GD27931@hirez.programming.kicks-ass.net>
Date:   Fri, 18 Jan 2019 15:52:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Networking Development Mailing List 
        <netdev@...r.kernel.org>
Subject: Re: [PATCH/RFC] Make perf_event_open() propagate errors for use in
 bpf_perf_event_open()

On Fri, Jan 11, 2019 at 12:55:38PM -0300, Arnaldo Carvalho de Melo wrote:
> Hi Peter,
> 
> 	bpf_perf_event_open() already returns a value, but if
> perf_event_output's output_begin (mostly perf_output_begin) fails,
> the only way to know about that is looking before/after the rb->lost,
> right?
> 
> 	For ring buffer users that is ok, we'll get a PERF_RECORD_LOST,
> etc, but for BPF programs it would be convenient to get that -ENOSPC and
> do some fallback, whatever makes sense, like in my augmented_syscalls
> stuff for 'perf trace', i.e. don't augment it (i.e. push stuff at the
> end of the normal payload), just don't filter the
> raw_syscalls:sys_enter, 'perf trace' will get the enter syscall enter
> event without the pointer dereference at the end, etc, warn the user but
> don't lose a syscall in the strace-like output.	
> 
> 	What do you think? Am I missing something? Probably ;-)

Seems ok to do this.