Re: [PATCH v5 2/8] perf list: Add scandirat compatibility function

[Namhyung Kim]

Hi Ian,

On Fri, Feb 16, 2024 at 3:55 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> scandirat is used during the printing of tracepoint events but may be
> missing from certain libcs. Add a compatibility implementation that
> uses the symlink of an fd in /proc as a path for the reliably present
> scandir.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

This fails to build in alpine:

  util/print-events.c: In function 'print_tracepoint_events':
  util/print-events.c:92:29: error: implicit declaration of function
'scandirat'; did you mean 'scandir'?
[-Werror=implicit-function-declaration]
  92 |                 evt_items = scandirat(events_fd,
sys_dirent->d_name, &evt_namelist, NULL, alphasort);
  |                             ^~~~~~~~~
  |                             scandir

Thanks,
Namhyung


> ---
>  tools/perf/util/print-events.c | 12 +++---------
>  tools/perf/util/util.c         | 19 +++++++++++++++++++
>  tools/perf/util/util.h         |  8 ++++++++
>  3 files changed, 30 insertions(+), 9 deletions(-)
>
> diff --git a/tools/perf/util/print-events.c b/tools/perf/util/print-events.c
> index 9e47712507cc..bf79dd366e2e 100644
> --- a/tools/perf/util/print-events.c
> +++ b/tools/perf/util/print-events.c
> @@ -63,6 +63,8 @@ void print_tracepoint_events(const struct print_callbacks *print_cb __maybe_unus
>  {
>         char *events_path = get_tracing_file("events");
>         int events_fd = open(events_path, O_PATH);
> +       struct dirent **sys_namelist = NULL;
> +       int sys_items;
>
>         put_tracing_file(events_path);
>         if (events_fd < 0) {
> @@ -70,10 +72,7 @@ void print_tracepoint_events(const struct print_callbacks *print_cb __maybe_unus
>                 return;
>         }
>
> -#ifdef HAVE_SCANDIRAT_SUPPORT
> -{
> -       struct dirent **sys_namelist = NULL;
> -       int sys_items = tracing_events__scandir_alphasort(&sys_namelist);
> +       sys_items = tracing_events__scandir_alphasort(&sys_namelist);
>
>         for (int i = 0; i < sys_items; i++) {
>                 struct dirent *sys_dirent = sys_namelist[i];
> @@ -130,11 +129,6 @@ void print_tracepoint_events(const struct print_callbacks *print_cb __maybe_unus
>         }
>
>         free(sys_namelist);
> -}
> -#else
> -       printf("\nWARNING: Your libc doesn't have the scandirat function, please ask its maintainers to implement it.\n"
> -              "         As a rough fallback, please do 'ls %s' to see the available tracepoint events.\n", events_path);
> -#endif
>         close(events_fd);
>  }
>
> diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
> index c1fd9ba6d697..4f561e5e4162 100644
> --- a/tools/perf/util/util.c
> +++ b/tools/perf/util/util.c
> @@ -552,3 +552,22 @@ int sched_getcpu(void)
>         return -1;
>  }
>  #endif
> +
> +#ifndef HAVE_SCANDIRAT_SUPPORT
> +int scandirat(int dirfd, const char *dirp,
> +             struct dirent ***namelist,
> +             int (*filter)(const struct dirent *),
> +             int (*compar)(const struct dirent **, const struct dirent **))
> +{
> +       char path[PATH_MAX];
> +       int err, fd = openat(dirfd, dirp, O_PATH);
> +
> +       if (fd < 0)
> +               return fd;
> +
> +       snprintf(path, sizeof(path), "/proc/%d/fd/%d", getpid(), fd);
> +       err = scandir(path, namelist, filter, compar);
> +       close(fd);
> +       return err;
> +}
> +#endif
> diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
> index 7c8915d92dca..9966c21aaf04 100644
> --- a/tools/perf/util/util.h
> +++ b/tools/perf/util/util.h
> @@ -6,6 +6,7 @@
>  /* glibc 2.20 deprecates _BSD_SOURCE in favour of _DEFAULT_SOURCE */
>  #define _DEFAULT_SOURCE 1
>
> +#include <dirent.h>
>  #include <fcntl.h>
>  #include <stdbool.h>
>  #include <stddef.h>
> @@ -56,6 +57,13 @@ int perf_tip(char **strp, const char *dirpath);
>  int sched_getcpu(void);
>  #endif
>
> +#ifndef HAVE_SCANDIRAT_SUPPORT
> +int scandirat(int dirfd, const char *dirp,
> +             struct dirent ***namelist,
> +             int (*filter)(const struct dirent *),
> +             int (*compar)(const struct dirent **, const struct dirent **));
> +#endif
> +
>  extern bool perf_singlethreaded;
>
>  void perf_set_singlethreaded(void);
> --
> 2.44.0.rc0.258.g7320e95886-goog
>