Re: [PATCH 5/6] libtracefs: Option's bit masks to be owned by the instance

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

On Fri, Apr 2, 2021 at 4:20 PM Yordan Karadzhov (VMware)
<y.karadz@gmail.com> wrote:
>
> If the instance owns two mask objects, we no longer need to
> dynamically allocate memory in tracefs_options_get_supported() and
> tracefs_options_get_enabled(). This will simplify the code on the
> caller side, since the user is no longer responsible for freeing
> those masks.
>
> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
> ---
>  Documentation/libtracefs-option-get.txt |  4 +---
>  include/tracefs.h                       |  6 +++---
>  src/tracefs-instance.c                  | 24 ++++++++++++------------
>  3 files changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/libtracefs-option-get.txt b/Documentation/libtracefs-option-get.txt
> index 9b3cb56..3290f24 100644
> --- a/Documentation/libtracefs-option-get.txt
> +++ b/Documentation/libtracefs-option-get.txt
> @@ -52,14 +52,13 @@ EXAMPLE
>  --
>  #include <tracefs.h>
>  ...
> -struct tracefs_options_mask *options;
> +const struct tracefs_options_mask *options;
>  ...
>  options = tracefs_options_get_supported(NULL);
>  if (!options) {
>         /* Failed to get supported options */
>  } else {
>         ...
> -       free(options);
>  }
>  ..

The description of the return value of tracefs_options_get_supported()
and tracefs_options_get_enabled() should be changed also, as it
suggests to free the return value;

>  options = tracefs_options_get_enabled(NULL);
> @@ -67,7 +66,6 @@ if (!options) {
>         /* Failed to get options, enabled in the top instance */
>  } else {
>         ...
> -       free(options);
>  }
>  ...
>
> diff --git a/include/tracefs.h b/include/tracefs.h
> index 0665e8d..9efa91a 100644
> --- a/include/tracefs.h
> +++ b/include/tracefs.h
> @@ -132,11 +132,11 @@ enum tracefs_option_id {
>  #define TRACEFS_OPTION_MAX (TRACEFS_OPTION_VERBOSE + 1)
>
>  struct tracefs_options_mask;
> -bool tracefs_option_is_set(struct tracefs_options_mask *options,
> +bool tracefs_option_is_set(const struct tracefs_options_mask *options,
>                            enum tracefs_option_id id);
> -struct tracefs_options_mask *tracefs_options_get_supported(struct tracefs_instance *instance);
> +const struct tracefs_options_mask *tracefs_options_get_supported(struct tracefs_instance *instance);
>  bool tracefs_option_is_supported(struct tracefs_instance *instance, enum tracefs_option_id id);
> -struct tracefs_options_mask *tracefs_options_get_enabled(struct tracefs_instance *instance);
> +const struct tracefs_options_mask *tracefs_options_get_enabled(struct tracefs_instance *instance);
>  bool tracefs_option_is_enabled(struct tracefs_instance *instance, enum tracefs_option_id id);
>  int tracefs_option_enable(struct tracefs_instance *instance, enum tracefs_option_id id);
>  int tracefs_option_diasble(struct tracefs_instance *instance, enum tracefs_option_id id);
> diff --git a/src/tracefs-instance.c b/src/tracefs-instance.c
> index 49645eb..9cb4b6d 100644
> --- a/src/tracefs-instance.c
> +++ b/src/tracefs-instance.c
> @@ -27,6 +27,8 @@ struct tracefs_instance {
>         char    *trace_dir;
>         char    *name;
>         int     flags;
> +       struct tracefs_options_mask     supported_opts;
> +       struct tracefs_options_mask     enabled_opts;
>  };
>
>  /**
> @@ -695,9 +697,8 @@ static struct tracefs_options_mask *trace_get_options(struct tracefs_instance *i
>         DIR *dir = NULL;
>         long long val;
>
> -       bitmask = calloc(1, sizeof(struct tracefs_options_mask));
> -       if (!bitmask)
> -               return NULL;
> +       bitmask = enabled? &instance->enabled_opts : &instance->supported_opts;

This makes the API not thread safe. There should be no problem with
supported options, as they cannot be changed at runtime. I think it is
OK to limit the APIs , as I see no use case to call them from multiple
threads on the same instance, but this should be described in the
documentation.

> +
>         dname = tracefs_instance_get_file(instance, "options");
>         if (!dname)
>                 goto error;
> @@ -727,7 +728,6 @@ error:
>         if (dir)
>                 closedir(dir);
>         tracefs_put_tracing_file(dname);
> -       free(bitmask);
>         return NULL;
>  }
>
> @@ -735,10 +735,10 @@ error:
>   * tracefs_options_get_supported - Get all supported trace options in given instance
>   * @instance: ftrace instance, can be NULL for the top instance
>   *
> - * Returns allocated bitmask structure with all trace options, supported in given
> - * instance, or NULL in case of an error. The returned structure must be freed with free()
> + * Returns bitmask structure with all trace options, supported in given instance,
> + * or NULL in case of an error.
>   */
> -struct tracefs_options_mask *tracefs_options_get_supported(struct tracefs_instance *instance)
> +const struct tracefs_options_mask *tracefs_options_get_supported(struct tracefs_instance *instance)
>  {
>         return trace_get_options(instance, false);

As supported options cannot be changed at runtime, they can be read
only once. The next calls can return the already initialised bitmask
with supported options.

>  }
> @@ -747,10 +747,10 @@ struct tracefs_options_mask *tracefs_options_get_supported(struct tracefs_instan
>   * tracefs_options_get_enabled - Get all currently enabled trace options in given instance
>   * @instance: ftrace instance, can be NULL for the top instance
>   *
> - * Returns allocated bitmask structure with all trace options, enabled in given
> - * instance, or NULL in case of an error. The returned structure must be freed with free()
> + * Returns allocated bitmask structure with all trace options, enabled in given instance,
> + * or NULL in case of an error.
>   */
> -struct tracefs_options_mask *tracefs_options_get_enabled(struct tracefs_instance *instance)
> +const struct tracefs_options_mask *tracefs_options_get_enabled(struct tracefs_instance *instance)
>  {
>         return trace_get_options(instance, true);
>  }
> @@ -758,7 +758,7 @@ struct tracefs_options_mask *tracefs_options_get_enabled(struct tracefs_instance
>  static int trace_config_option(struct tracefs_instance *instance,
>                                enum tracefs_option_id id, bool set)
>  {
> -       char *set_str = set ? "1" : "0";
> +       const char *set_str = set ? "1" : "0";
>         char file[PATH_MAX];
>         const char *name;
>
> @@ -846,7 +846,7 @@ bool tracefs_option_is_enabled(struct tracefs_instance *instance, enum tracefs_o
>   * Returns true if an option with given id is set in the bitmask,
>   * false if it is not set.
>   */
> -bool tracefs_option_is_set(struct tracefs_options_mask *options,
> +bool tracefs_option_is_set(const struct tracefs_options_mask *options,
>                            enum tracefs_option_id id)
>  {
>         if (id > TRACEFS_OPTION_INVALID)
> --
> 2.27.0
>


-- 
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center