Re: [PATCH v3 05/10] libperf: Add libperf_evsel__mmap()

[Jiri Olsa]

On Fri, Sep 11, 2020 at 03:51:13PM -0600, Rob Herring wrote:
> In order to support usersapce access, an event must be mmapped. While
> there's already mmap support for evlist, the usecase is a bit different
> than the self monitoring with userspace access. So let's add a new
> perf_evsel__mmap() function to mmap an evsel. This allows implementing
> userspace access as a fastpath for perf_evsel__read().
> 
> The mmapped address is returned by perf_evsel__mmap() primarily for
> users/tests to check if userspace access is enabled.
> 
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> ---
> v3:
>  - New patch split out from user access patch
> ---
>  tools/lib/perf/Documentation/libperf.txt |  1 +
>  tools/lib/perf/evsel.c                   | 31 ++++++++++++++++++++++++
>  tools/lib/perf/include/internal/evsel.h  |  2 ++
>  tools/lib/perf/include/perf/evsel.h      |  2 ++
>  tools/lib/perf/libperf.map               |  1 +
>  5 files changed, 37 insertions(+)
> 
> diff --git a/tools/lib/perf/Documentation/libperf.txt b/tools/lib/perf/Documentation/libperf.txt
> index 0c74c30ed23a..0b4694ce42b9 100644
> --- a/tools/lib/perf/Documentation/libperf.txt
> +++ b/tools/lib/perf/Documentation/libperf.txt
> @@ -136,6 +136,7 @@ SYNOPSIS
>                         struct perf_thread_map *threads);
>    void perf_evsel__close(struct perf_evsel *evsel);
>    void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu);
> +  void *perf_evsel__mmap(struct perf_evsel *evsel, size_t length);
>    int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
>                         struct perf_counts_values *count);
>    int perf_evsel__enable(struct perf_evsel *evsel);
> diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> index 4dc06289f4c7..99fa53dc0887 100644
> --- a/tools/lib/perf/evsel.c
> +++ b/tools/lib/perf/evsel.c
> @@ -11,10 +11,12 @@
>  #include <stdlib.h>
>  #include <internal/xyarray.h>
>  #include <internal/cpumap.h>
> +#include <internal/mmap.h>
>  #include <internal/threadmap.h>
>  #include <internal/lib.h>
>  #include <linux/string.h>
>  #include <sys/ioctl.h>
> +#include <sys/mman.h>
>  
>  void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr)
>  {
> @@ -156,6 +158,35 @@ void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu)
>  	perf_evsel__close_fd_cpu(evsel, cpu);
>  }
>  
> +void *perf_evsel__mmap(struct perf_evsel *evsel, size_t length)
> +{

could you rather use 'int pages' insted of length as we
do in perf_evlist__mmap, so we keep the same interface

  len = (pages + 1) * page_size

thanks,
jirka