Re: [RFC PATCH v2 1/3] trace2: Add a JSON schema for trace2 events

> Define a JSON schema[1] that can be used to validate trace2 event
> objects. This can be used to add regression tests to verify that the
> event output format does not change unexpectedly.
>
> Two versions of the schema are provided:

> * event_schema.json is more permissive. It verifies that all expected
>   fields are present in each trace event, but it allows traces to have
>   unexpected additional fields. This allows the schema to be specified
>   more concisely by factoring out the common fields into a reusable
>   sub-schema.
> * strict_schema.json is more restrictive. It verifies that all expected
>   fields are present and no unexpected fields are present in each trace
>   event. Due to this additional restriction, the common fields cannot be
>   factored out into a re-usable subschema (at least as-of draft-07) [2],
>   and must be repeated for each event definition.
>
> [1]: https://json-schema.org/
> [2]: https://json-schema.org/understanding-json-schema/reference/combining.html#allof
>
> Signed-off-by: Josh Steadmon <steadmon@google.com>
> ---
>  t/trace_schema_validator/README               |  23 +
>  t/trace_schema_validator/event_schema.json    | 398 ++++++++++++++
>  t/trace_schema_validator/list_schema.json     | 401 ++++++++++++++
>  .../strict_list_schema.json                   | 514 ++++++++++++++++++
>  t/trace_schema_validator/strict_schema.json   | 511 +++++++++++++++++
>  5 files changed, 1847 insertions(+)
>  create mode 100644 t/trace_schema_validator/README
>  create mode 100644 t/trace_schema_validator/event_schema.json
>  create mode 100644 t/trace_schema_validator/list_schema.json
>  create mode 100644 t/trace_schema_validator/strict_list_schema.json
>  create mode 100644 t/trace_schema_validator/strict_schema.json
>
> diff --git a/t/trace_schema_validator/README b/t/trace_schema_validator/README
> new file mode 100644
> index 0000000000..45f0e6f0c4
> --- /dev/null
> +++ b/t/trace_schema_validator/README
> @@ -0,0 +1,23 @@
> +These JSON schemas[1] can be used to validate trace2 event objects. They
> +can be used to add regression tests to verify that the event output
> +format does not change unexpectedly.
> +
> +Four versions of the schema are provided:
> +* event_schema.json is more permissive. It verifies that all expected
> +  fields are present in a trace event, but it allows traces to have
> +  unexpected additional fields. This allows the schema to be specified
> +  more concisely by factoring out the common fields into a reusable
> +  sub-schema.
> +* strict_schema.json is more restrictive. It verifies that all expected
> +  fields are present and no unexpected fields are present in the trace
> +  event. Due to this additional restriction, the common fields cannot be
> +  factored out into a re-usable subschema (at least as-of draft-07) [2],
> +  and must be repeated for each event definition.
> +* list_schema.json is like event_schema.json above, but validates a JSON
> +  array of trace events, rather than a single event.
> +* strict_list_schema.json is like strict_schema.json above, but
> +  validates a JSON array of trace events, rather than a single event.
> +
> +[1]: https://json-schema.org/
> +[2]: https://json-schema.org/understanding-json-schema/reference/combining.html#allof