pkg/run: Don't rely on GADGET_TRACER as it is optional

[blanquicet]

Don't rely on GADGET_TRACER as it is optional

GetTracerInfo gets the tracer information from what was defined by
the GADGET_TRACER macro. However, such macro is optional, so we
must not rely on it. Additionally, by the time
handleTracerMapDefinition() is called, the metadata was already
built (either from the metadata file or from the eBPF code), so we
can get the tracer information from there.

[eiffel-fl]

Hi.

From code inspection, this looks OK.
However, I would question the whole existence of this macro.
If it is optional, we should just drop it and not add another level of complexity.
Otherwise, we should document in which case it is mandatory to use it. I suspect this documentation to no more be up to date:

inspektor-gadget/docs/devel/hello-world-gadget.md

Lines 284 to 285 in 1072df2

	> The `tracers` and `structs` sections will only be generated if the eBPF program defined a tracer
	> using the `GADGET_TRACER` macro.

Best regards.

[blanquicet]

Hi.

Hola Francis 🙂

I would question the whole existence of this macro. If it is optional, we should just drop it and not add another level of complexity. Otherwise, we should document in which case it is mandatory to use it.

The macro GADGET_TRACER is only useful to allow IG autogenerating the tracers and structs section of the metadata file. However, if developer created the metadata manually, the macro is not necessary anymore. That's why it is optional. That's also why the documentation says "The tracers and structs sections will only be generated if the eBPF program defined a tracer using the GADGET_TRACER macro", so ...

I suspect this documentation to no more be up to date:

... no, it is up to date. Actually, I recently updated it in this PR the documentation to make this optionality clearer:

inspektor-gadget/docs/devel/hello-world-gadget.md

Lines 86 to 92 in 1072df2

	This information enables Inspektor Gadget to generate the metadata file automatically.
	Refer to the [metadata file](#creating-a-metadata-file) section for detailed instructions.
	```c
	// [Optional] Define a tracer
	GADGET_TRACER(open, events, event);
	```

If you consider it is not yet clear enough, would you mind opening a PR to improve the documentation?

[eiffel-fl]

Hi.

Hola Francis 🙂

I would question the whole existence of this macro. If it is optional, we should just drop it and not add another level of complexity. Otherwise, we should document in which case it is mandatory to use it.

The macro GADGET_TRACER is only useful to allow IG autogenerating the tracers and structs section of the metadata file. However, if developer created the metadata manually, the macro is not necessary anymore. That's why it is optional. That's also why the documentation says "The tracers and structs sections will only be generated if the eBPF program defined a tracer using the GADGET_TRACER macro", so ...

I suspect this documentation to no more be up to date:

... no, it is up to date. Actually, I recently updated it in this PR the documentation to make this optionality clearer:

inspektor-gadget/docs/devel/hello-world-gadget.md

Lines 86 to 92 in 1072df2

	This information enables Inspektor Gadget to generate the metadata file automatically.
	Refer to the [metadata file](#creating-a-metadata-file) section for detailed instructions.
	```c
	// [Optional] Define a tracer
	GADGET_TRACER(open, events, event);
	```

If you consider it is not yet clear enough, would you mind opening a PR to improve the documentation?

If this metadata file is optional, then why do we need it?
We should go straight to the point and not bothering about optional stuff, if this is optional, we just drop it and move forward.

[mauriciovasquezbernal]

If this metadata file is optional, then why do we need it?

The metadata file allows to define extra attributes for the gadget as the format used to print the fields, and in the future documentation and all other stuff we can't put directly in the eBPF code. It's optional because the gadget can work without it, we don't want to force gadget developers creating this file if they don't want to define any of these extra attributes.

[blanquicet]

If this metadata file is optional, then why do we need it?

The metadata file allows to define extra attributes for the gadget as the format used to print the fields, and in the future documentation and all other stuff we can't put directly in the eBPF code. It's optional because the gadget can work without it, we don't want to force gadget developers creating this file if they don't want to define any of these extra attributes.

I agree the metadata file should be optional, but I'm not fully convinced about the GADGET_TRACER. Do you really expect users to create the metadata file manually? I'm not that convinced. In addition, even if they define it by hand, they won't be able to keep it automatically updated using the --update-metadata flag without defining the GADGET_TRACER.

Let's discuss it in IG Developer Sync meeting today.