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Date: Thu, 25 May 2017 10:09:17 +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>,
        David Ahern <dsa@cumulusnetworks.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>, Paul Turner <pjt@google.com>
Subject: Re: [PATCH v2 10/13] perf header: add a buffer to struct feat_fd
Message-ID: <20170525080917.GJ14467@krava>
References: <20170523074853.54892-1-davidcc@google.com>
 <20170523074853.54892-11-davidcc@google.com>
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On Tue, May 23, 2017 at 12:48:50AM -0700, David Carrillo-Cisneros wrote:

SNIP

> @@ -795,11 +831,19 @@ static int write_pmu_mappings(struct feat_fd *fd,
>  			      struct perf_evlist *evlist __maybe_unused)
>  {
>  	struct perf_pmu *pmu = NULL;
> -	off_t offset = lseek(fd->fd, 0, SEEK_CUR);
> -	__u32 pmu_num = 0;
> +	u32 pmu_num = 0;
>  	int ret;
>  
> -	/* write real pmu_num later */
> +	/*
> +	 * Do a first pass to count number of pmu to avoid lseek so this
> +	 * works in pipe mode as well.
> +	 */
> +	while ((pmu = perf_pmu__scan(pmu))) {
> +		if (!pmu->name)
> +			continue;
> +		pmu_num++;
> +	}

please put this functionality into preceeding separate patch

thanks,
jirka