upg-vpp | User Plane Gateway (UPG) based on VPP

Design rationale for the development environment is this:. Relevant parts of the source tree layout: * hack/ contains helper scripts most of which are wrapped in make commands * Makefile provides user interface for the environment * upf/ contains the source code of the plugin^{[1](#footnote-1)} * upf/test/ contains the integration tests^{[1](#footnote-1)} * vpp/ contains VPP source code and is not committed * vpp-patches/ contains patches to apply to the upstream VPP code (applied automatically via git am; generated by hand with git format-patch) * vpp.spec contains the info on VPP repo, branch and commit to use. upg/ is symlinked to the VPP plugins directory, one can just go to vpp/ directory after make update-vpp and follow [upstream VPP build instructions][VPPBUILD]. But, as an alternative, UPG does provide some build helpers of its own. There’s a simple dockerized environment wrapped in make commands. During the development cycle, VPP is cloned into vpp/ subdirectory from an upstream repository with some of the [patches](vpp-patches/) applied. This is done automatically but can also be done via make update-vpp which will delete all of the changes made to vpp/ directory. You can make temporary changes under vpp/ for debugging purposes. The "build image" which is used for the devenv is tagged with a hash of Dockerfile.build as well as VPP’s external dependencies.
provide an easily reproducible development and build environment usable both on CI and locally
provide quick commands for common tasks
simplify bisecting against upstream VPP
discourage downstream VPP changes, as we should make effort to upstream them
make image-debug builds a debug UPG Docker image named upg:debug
make image-release builds a release UPG Docker image named upg:release
make test-debug, make test-release build VPP and run UPG integration tests in debug and release mode respectively. The compilation results are retained under vpp/
make retest-debug, make retest-release run UPG integration tests in debug and release mode respectively without building VPP. These can be run under make test-debug / make test-release to re-run the tests quickly if there were no UPG / VPP code changes
make ensure-build-image checks if the build image exists or can be pulled and builds it otherwise
make update-build-image-tag updates the build image tag in the Dockerfiles according to the hash calculated from Dockerfile.build and VPP external dependencies
make install-hooks installs git hooks in the repo which prevent the user from making commits that contain ZZZZZ: substring. This is handy for debug print like clib_warning("ZZZZZ: i %d", i);
make update-vpp re-clones VPP into vpp/ directory
make buildenv runs an interactive shell inside the build environment with UPG and VPP sources mounted into the container
make e2e-debug and make e2e-release build UPG in debug and release mode respectively and run E2E tests for it. For more information, see [E2E test documentation](test/e2e/README.md)
make checkstyle performs style checks on the source code