linux-kernel - Re: [PATCH 01/10] perf evlist: Introduce perf_evlist__filter

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Date:	Mon, 25 Aug 2014 09:57:53 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 01/10] perf evlist: Introduce perf_evlist__filter_pollfd
 method

On 08/22/2014 11:59 PM, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> To remove all entries in evlist->pollfd[] that have revents matching at
> least one of the bits in the specified mask.
> 
> It'll adjust evlist->nr_fds to the number of unfiltered fds and will
> return this value, as a convenience and to avoid requiring direct access
> to internal state of perf_evlist objects.
> 
> This will be used after polling the evlist fds so that we remove fds
> that were closed by the kernel.
> 
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Don Zickus <dzickus@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephane Eranian <eranian@...gle.com>
> Link: http://lkml.kernel.org/n/tip-ki3oqbfjg84si3f9amhyqvzb@git.kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/util/evlist.c | 16 ++++++++++++++++
>  tools/perf/util/evlist.h |  2 ++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index a3e28b49128a..bd7896073d10 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -428,6 +428,22 @@ void perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
>  	evlist->nr_fds++;
>  }
>  
> +int perf_evlist__filter_pollfd(struct perf_evlist *evlist, short revents_and_mask)
> +{
> +	int fd = 0, nr_fds = 0;
> +
> +	while (fd < evlist->nr_fds) {

A for loop is clearer e.g.

	for (fd = 0; fd < evlist->nr_fds; fd++) {


> +		if ((evlist->pollfd[fd].revents & revents_and_mask) == 0)
> +			++nr_fds;
> +
> +		if (++fd != nr_fds)
> +			evlist->pollfd[nr_fds] = evlist->pollfd[fd];

That looks like it will go off the end of the array.  Shouldn't it be:

		if ((evlist->pollfd[fd].revents & revents_and_mask) == 0) {
			if (fd != nr_fds)
				evlist->pollfd[nr_fds] = evlist->pollfd[fd];
			nr_fds += 1;
		}

> +	}
> +
> +	evlist->nr_fds = nr_fds;
> +	return nr_fds;
> +}
> +
>  static void perf_evlist__id_hash(struct perf_evlist *evlist,
>  				 struct perf_evsel *evsel,
>  				 int cpu, int thread, u64 id)
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 106de53a6a74..1082420951f9 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -84,6 +84,8 @@ void perf_evlist__id_add(struct perf_evlist *evlist, struct perf_evsel *evsel,
>  
>  void perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd);
>  
> +int perf_evlist__filter_pollfd(struct perf_evlist *evlist, short revents_and_mask);
> +
>  struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id);
>  
>  struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id);
> 

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