IDPF dependencies in TdiTableManager

[ffoulkes]

Synopsis

TdiTableManager supports the PacketModMeter and DirectPacketModMeter P4Externs, which are ES2K-specific. To support them, TableManager #includes idpf/p4info.pb.h, which is only available in the ipdk-io/p4runtime-dev repository.

This is undesirable, since it couples the DPDK and Tofino platforms to a version of P4Runtime that has been customized for ES2K.

Expected behavior

TdiTableManager should provide for target-specific handling of P4 resources, incorporated as part of the build.

Proposed solution

This is somewhat kludgy, but it changes less code and is easier to review than the more general solution, which is described in issue #304.

1. Define a generic base class (TdiTableAnnex) and a subclass for each target that requires one (Es2kTableAnnex).
2. Modify each site in TdiTableManager that performs target-specific processing to support a P4Extern, and add a method to the TableAnnex classes.
3. Move the ES2K-specific code from TdiTableManager to the corresponding method in Es2kTableAnnex, and replace the original with a call to the method.
4. Add a method toTdiTargetFactory that creates a TableAnnex class of the correct type.
5. This will allow us to isolate the ES2K-specific code and prevent it from being included by the other targets.

Sample code

With this approach, the following code fragment:

if (resource_type == "DirectPacketModMeter" &&
    table_entry.has_meter_config()) {
  bool units_in_packets;  // or bytes
  ASSIGN_OR_RETURN(
      auto meter,
      tdi_extern_manager_->FindDirectPktModMeterByID(resource_id));
  RETURN_IF_ERROR(GetMeterUnitsInPackets(meter, units_in_packets));

  TdiPktModMeterConfig config;
  config.SetTableEntry(table_entry);
  config.isPktModMeter = units_in_packets;

  RETURN_IF_ERROR(table_data->SetPktModMeterConfig(config));
}

becomes this:

if (resource_type == "DirectPacketModMeter") {
  RETURN_IF_ERROR(tdi_table_annex_->BuildDirPktModTableData(
      table_entry, table_data, resource_id));
}

Class model