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Date: Thu, 8 Jun 2017 13:54:22 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: David Carrillo-Cisneros <davidcc@google.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>, Simon Que <sque@chromium.org>,
        Wang Nan <wangnan0@huawei.com>, Jiri Olsa <jolsa@kernel.org>,
        He Kuang <hekuang@huawei.com>, Masami Hiramatsu <mhiramat@kernel.org>,
        Stephane Eranian <eranian@google.com>, Paul Turner <pjt@google.com>
Subject: Re: [PATCH v3 11/15] perf header: add a buffer to struct feat_fd
Message-ID: <20170608115422.GA29151@krava>
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 <20170606070722.35213-12-davidcc@google.com>
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On Tue, Jun 06, 2017 at 12:07:18AM -0700, David Carrillo-Cisneros wrote:

SNIP

>  static int do_read_u32(struct feat_fd *ff, u32 *addr)
> @@ -188,6 +233,10 @@ static char *do_read_string(struct feat_fd *ff)
>  static int write_tracing_data(struct feat_fd *ff,
>  			      struct perf_evlist *evlist)
>  {
> +	if (ff->buf) {
> +		WARN_ON("Pipe-mode doesn't supported write_tracing_data.\n");
> +		return -1;
> +	}

I think you need to use WARN or WARN_ONCE here, like:

	if (WARN_ONCE(ff->buf, "Pipe....."))
		return -1;

WARN_ON takes condition as an argument not string

jirka