[waffle] [PATCH 06/12] wflinfo: add option for JSON output

[Chad Versace]

On 01/06/2016 11:56 AM, Frank Henigman wrote:
> With "-f json" wflinfo will now print the result of
> waffle_display_info_json().
> 
> Signed-off-by: Frank Henigman <fjhenigman at google.com>
> ---
>  src/utils/wflinfo.c | 40 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 36 insertions(+), 4 deletions(-)
> 
> diff --git a/src/utils/wflinfo.c b/src/utils/wflinfo.c
> index 268d4b8..58f5688 100644
> --- a/src/utils/wflinfo.c
> +++ b/src/utils/wflinfo.c


> @@ -1119,9 +1137,23 @@ main(int argc, char **argv)
>          glGetStringi = waffle_get_proc_address("glGetStringi");
>      }
>  
> -    ok = print_wflinfo(&opts);
> -    if (!ok)
> -        error_waffle();
> +    char *info;
> +    switch (opts.format) {
> +        case FORMAT_ORIGINAL:
> +            ok = print_wflinfo(&opts);
> +            if (!ok)
> +                error_waffle();
> +            break;
> +
> +        case FORMAT_JSON:
> +            info = waffle_display_info_json(dpy, false);
> +            if (info) {
> +                printf("%s\n", info);
> +                free(info);
> +            } else
> +                error_waffle();
> +            break;
> +    }


I agree with the patch series's goals: teach wflinfo to print platform-specific
info (such as EGL info); extract that info inside libwaffle and expose it
through public API; that public API should provide JSON, and perhaps additional
formats.

But this patch 6/12 poses a problem. Post-patch, wflinfo can print its info in
the old format and in a json format. But, depending on the output format,
wflinfo uses completely separate code paths to obtain the information.

The actual information that wflinfo provides, and the method by which it
obtains that info, should be largely independent of the output format. When the
user chooses an output format, that choice should affect the *presentation* but
not fundamentally affect the *content*.

So...

For wflinfo's sake, we need a public waffle_get_my_info() function that returns
data that can be translated into the old format and into the json format, or perhaps
returns the old format and json directly.

To move forward with this patch series, I see the following options:

    1. waffle_get_my_info() returns only json

      I don't like this. This would require that wflinfo decode the json in
      order to provide the old format output. I would like to avoid decoding
      json in Waffle though, because that would require either (a) Waffle
      contain a json decoder implementation or (b) Waffle rely on some json
      library. As for (a), I don't want to maintain a json-decoder (a json
      *encoder*, though, I don't object to). As for (b), Waffle is such
      a small, focused project that it feels wrong to pull in a json-decoder
      library as a dependency.

      BUT, maybe this option could work and I'm overestimating the maintenance
      overhead of decoding json.

    2. waffle_get_my_info() returns only some-other-well-defined-format-FOO

       I don't like this either. Just like option 1, it would require that
       wflinfo decode the FOO format in order to provide json output.

    3. waffle_get_my_info() can return a json string or a string in the old
       wflinfo format

       If option 3 can be implemented cleanly, I think it's the best choice.
       This option eliminates the need for decoding any special format.

       Perhaps we could implement this by defining a private struct...

            struct wcore_display_info {
                struct {
                    char *platform;
                    char *api;
                } waffle;

                struct {
                    char *vendor;
                    char *renderer;
                    ...
                    char **extensions;
                } opengl;

                struct {
                    char *version;
                    char *vendor;
                    char *client_apis;
                    ...
                } egl;

                ...
            };

        ...that waffle_get_my_info() populates and then encodes into the
        respected format: JSON, the old wflinfo format, a format that
        mimics glxinfo, or whatever.


Frank, what do you think?