Flavors can contain "extra specs", or additional metadata about the flavor. Gophercloud currently does not have any support for this.

• List Extra Specs (Flavor Extra Specs: List / Get #686)
• Get an Extra Spec (Flavor Extra Specs: List / Get #686)
• Create an Extra Spec (Flavor Extra Specs Create  #689)
• Update an Extra Spec (Flavor Extra Spec Update #712)
• Delete an Extra Spec (Flavor Extra Spec Delete #705)

API reference:

• https://developer.openstack.org/api-ref/compute/#flavors-extra-specs-flavors-os-flavor-extra-specs

Nova implementation:

• https://github.com/openstack/nova/blob/stable/pike/nova/api/openstack/compute/flavors_extraspecs.py

Schema:

• https://github.com/openstack/nova/blob/stable/pike/nova/api/openstack/compute/schemas/flavors_extraspecs.py
• https://github.com/openstack/nova/blob/stable/pike/nova/api/validation/parameter_types.py#L333-L341

Extra Specs are defined just as Server Metadata is defined, so they will be a map[string]string.