Parameters

Parameters from eBPF programs

A Gadget can expose parameters to the client from the eBPF program. Inspektor Gadget provides the mechanism to expose the parameters as CLI flags to the user and allow to set them from the configuration file.

1. Define a constant. It's important to use const volatile for the verifier to remove dead code.

const volatile bool myparam = false;

2. Mark the constant as a parameter.

GADGET_PARAM(myparam);

3. Provide additional information for the param on the metadata file:

params:
  ebpf:
    myparam:
      key: my-param
      defaultValue: "false"
      description: Description for the param

Customizable parameters

Much of Inspektor Gadget's functionality is controlled by parameters and annotations. To give gadget authors more freedom, one can define new parameters that affect a group of other parameters, datasource and field annotations, operator's configuration or any other field in the metadata file. This works by patching the gadget metadata itself, depending on those custom parameters' values.

In the gadget.yaml, create a new section called custom to params like this:

params:
  custom:
    myCustomParam:
      description: A parameter that will apply a patch based on one of the possible values.
      defaultValue: "option1"
      values:
        option1:
          patch:
            datasources:
              myDataSource:
                annotations:
                  columns.output: none
    mySecondParam:
      description: Another parameter. This will apply a patch globally, regardless of the actual value.
      defaultValue: "default"
      patch:
        datasources:
          myDataSource:
            annotations:
              my.annotation: >-
                A template driven value, now {{call .getParamValue "custom.mySecondParam"}}.
              my.second.annotation: >-
                We can also access other configuration values, like the gadget name: {{call .getConfig "name"}}

All keys below custom will become new parameters that can be set by the user of the gadget. Depending on the parameters' value, a patch node will be applied to the gadget metadata itself. (See myCustomParam example above.)

If no specific values are configured, a global patch section will be applied. (See mySecondParam example above.)

Strings used can use templates (explained here). Functions available to the templating engine are:

getParamValue(paramName)

Can be used to get the value of any set parameter; paramName needs to be fully qualified, e.g. custom.mySecondParam or operator.oci.ebpf.target_family.

getConfig(key)

Can be used to get the value of any metadata key like name, params.custom.myCustomParam.description, etc.