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target_options.md

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TargetOptions Class

Background

Three changes were made to common files in order to support the TDI targets.

  1. When built for the DPDK target, ConfigMonitoringService::DoSet() no longer pushes the updated chassis configuration to the switch.

  2. When built for the DPDK target, P4Service::SetForwardingPipelineConfig() returns an error if an attempt is made to overwrite an existing pipeline.

  3. ConfigMonitoringService::PushSavedChassisConfig() returns an error if the configuration file path is a symlink. This change was made to mitigate a security weakness.

Changes 1 and 2 are controlled by #ifdef DPDK_TARGET. Change 3 is not conditionalized. It is currently disabled via #if 0 because it breaks unit test cases that use symlinks to manage the test environment.

Problem statement

  • The Stratum code has very few compile-time conditionals, none of which are in common code. The DPDK_TARGET conditionals go against this convention.

  • Compile-time conditionals complicate the Bazel build and lead to recompilation when we change targets. This is undesirable, especially in common source files.

  • Change 3 is sensitive to which target is being built and whether the code is being compiled for unit test purposes. We do not want to introduce more compile-time conditionals, and we do not want to have to recompile a file for unit testing.

Proposed solution

  • Introduce a parameter object (TargetOptions) that can be passed to the ConfigMonitoringService and P4Service classes to influence their behavior.

  • Define Boolean members to enable/disable each of the TDI changes.

  • Instantiate the object in the target's main class, initialize its member values according to the needs of the target, and pass the object to the service classes when instantiating them.

  • Have each option default to a value that maintains backward compatibility with previous versions of Stratum.

  • Make the TargetOptions parameter optional, with the default options being used if the parameter is not specified. This removes the need to update legacy code.

Source code

Changes:

  • Create target_options.cc and target_options.h.

  • Implementtarget_options parameter and target_options_ member variable in the DpdkHal, Es2kHal, ConfigMonitoringService, and P4Service classes.

  • Modify DpdkMain and Es2kMain to create and initialize a TargetOptions object and specify it when instantiating the DpdkHal and Es2kHal objects.

  • Modify DpdkHal and Es2kHal to specify the target_options parameter when creating the ConfigMonitoringService and P4Service objects.

  • Modify ConfigMonitoringService and P4Service to use the appropriate member of the TargetOptions class, instead of a compile-time conditional, to enable the new behavior in those classes.

  • Remove logic to define the DPDK_TARGET from the Bazel build files.

Notes:

  • The security mitigation in ConfigMonitoringService has been reenabled. The unit test that caused the mitigation to be disabled now passes.

  • There are no remaining occurrences of the DPDK_TARGET conditional in Stratum.

  • The Tofino target (which is in "minimal maintenance" state) is unmodified. It compiles, and its unit tests pass, providing some assurance that we have maintained backward compatibility with existing code.