DOC ONLY: cmake / ninja build system doc
Change-Id: I69cdcf3f0940f8a5f60203034688a0c63446f65c
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/docs/gettingstarted/developers/buildsystem/cmakeandninja.rst b/docs/gettingstarted/developers/buildsystem/cmakeandninja.rst
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+Introduction to cmake and ninja
+===============================
+
+Cmake plus ninja is approximately equal to GNU autotools plus GNU
+make, respectively. Both cmake and GNU autotools support self and
+cross-compilation, checking for required components and versions.
+
+- For a decent-sized project - such as vpp - build performance is drastically better with (cmake, ninja).
+
+- The cmake input language looks like an actual language, rather than a shell scripting scheme on steroids.
+
+- Ninja doesn't pretend to support manually-generated input files. Think of it as a fast, dumb robot which eats mildly legible byte-code.
+
+See the `cmake website <http://cmake.org>`_, and the `ninja website
+<https://ninja-build.org>`_ for additional information.
+
+vpp cmake configuration files
+-----------------------------
+
+The top of the vpp project cmake hierarchy lives in .../src/CMakeLists.txt.
+This file defines the vpp project, and (recursively) includes two kinds
+of files: rule/function definitions, and target lists.
+
+- Rule/function definitions live in .../src/cmake/{\*.cmake}. Although the contents of these files is simple enough to read, it shouldn't be necessary to modify them very often
+
+- Build target lists come from CMakeLists.txt files found in subdirectories, which are named in the SUBDIRS list in .../src/CMakeLists.txt
+
+::
+
+ ##############################################################################
+ # subdirs - order matters
+ ##############################################################################
+ if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
+ find_package(OpenSSL REQUIRED)
+ set(SUBDIRS
+ vppinfra svm vlib vlibmemory vlibapi vnet vpp vat vcl plugins
+ vpp-api tools/vppapigen tools/g2 tools/elftool tools/perftool)
+ elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")
+ set(SUBDIRS vppinfra)
+ else()
+ message(FATAL_ERROR "Unsupported system: ${CMAKE_SYSTEM_NAME}")
+ endif()
+
+ foreach(DIR ${SUBDIRS})
+ add_subdirectory(${DIR})
+ endforeach()
+
+- The vpp cmake configuration hierarchy discovers the list of plugins to be built by searching for subdirectories in .../src/plugins which contain CMakeLists.txt files
+
+
+::
+
+ ##############################################################################
+ # find and add all plugin subdirs
+ ##############################################################################
+ FILE(GLOB files RELATIVE
+ ${CMAKE_CURRENT_SOURCE_DIR}
+ ${CMAKE_CURRENT_SOURCE_DIR}/*/CMakeLists.txt
+ )
+ foreach (f ${files})
+ get_filename_component(dir ${f} DIRECTORY)
+ add_subdirectory(${dir})
+ endforeach()
+
+How to write a plugin CMakeLists.txt file
+-----------------------------------------
+
+It's really quite simple. Follow the pattern:
+
+::
+
+ add_vpp_plugin(mactime
+ SOURCES
+ mactime.c
+ node.c
+
+ API_FILES
+ mactime.api
+
+ INSTALL_HEADERS
+ mactime_all_api_h.h
+ mactime_msg_enum.h
+
+ API_TEST_SOURCES
+ mactime_test.c
+ )
+
+Adding a target elsewhere in the source tree
+--------------------------------------------
+
+Within reason, adding a subdirectory to the SUBDIRS list in
+.../src/CMakeLists.txt is perfectly OK. The indicated directory will
+need a CMakeLists.txt file.
+
+Here's how we build the g2 event data visualization tool:
+
+::
+
+ option(VPP_BUILD_G2 "Build g2 tool." OFF)
+ if(VPP_BUILD_G2)
+ find_package(GTK2 COMPONENTS gtk)
+ if(GTK2_FOUND)
+ include_directories(${GTK2_INCLUDE_DIRS})
+ add_vpp_executable(g2
+ SOURCES
+ clib.c
+ cpel.c
+ events.c
+ main.c
+ menu1.c
+ pointsel.c
+ props.c
+ g2version.c
+ view1.c
+
+ LINK_LIBRARIES vppinfra Threads::Threads m ${GTK2_LIBRARIES}
+ NO_INSTALL
+ )
+ endif()
+ endif()
+
+The g2 component is optional, and is not built by default. There are
+a couple of ways to tell cmake to include it in build.ninja [or in Makefile.]
+
+When invoking cmake manually [rarely done and not very easy], specify
+-DVPP_BUILD_G2=ON:
+
+::
+
+ $ cmake ... -DVPP_BUILD_G2=ON
+
+Take a good look at .../build-data/packages/vpp.mk to see where and
+how the top-level Makefile and .../build-root/Makefile set all of the
+cmake arguments. One strategy to enable an optional component is fairly
+obvious. Add -DVPP_BUILD_G2=ON to vpp_cmake_args.
+
+That would work, of course, but it's not a particularly elegant solution.
+
+Tinkering with build options: ccmake
+------------------------------------
+
+The easy way to set VPP_BUILD_G2 - or frankly **any** cmake
+parameter - is to install the "cmake-curses-gui" package and use
+it.
+
+- Do a straightforward vpp build using the top level Makefile, "make build" or "make build-release"
+- Ajourn to .../build-root/build-vpp-native/vpp or .../build-root/build-vpp_debug-native/vpp
+- Invoke "ccmake ." to reconfigure the project as desired
+
+Here's approximately what you'll see:
+
+::
+
+ CCACHE_FOUND /usr/bin/ccache
+ CMAKE_BUILD_TYPE
+ CMAKE_INSTALL_PREFIX /scratch/vpp-gate/build-root/install-vpp-nati
+ DPDK_INCLUDE_DIR /scratch/vpp-gate/build-root/install-vpp-nati
+ DPDK_LIB /scratch/vpp-gate/build-root/install-vpp-nati
+ MBEDTLS_INCLUDE_DIR /usr/include
+ MBEDTLS_LIB1 /usr/lib/x86_64-linux-gnu/libmbedtls.so
+ MBEDTLS_LIB2 /usr/lib/x86_64-linux-gnu/libmbedx509.so
+ MBEDTLS_LIB3 /usr/lib/x86_64-linux-gnu/libmbedcrypto.so
+ MUSDK_INCLUDE_DIR MUSDK_INCLUDE_DIR-NOTFOUND
+ MUSDK_LIB MUSDK_LIB-NOTFOUND
+ PRE_DATA_SIZE 128
+ VPP_API_TEST_BUILTIN ON
+ VPP_BUILD_G2 OFF
+ VPP_BUILD_PERFTOOL OFF
+ VPP_BUILD_VCL_TESTS ON
+ VPP_BUILD_VPPINFRA_TESTS OFF
+
+ CCACHE_FOUND: Path to a program.
+ Press [enter] to edit option Press [d] to delete an entry CMake Version 3.10.2
+ Press [c] to configure
+ Press [h] for help Press [q] to quit without generating
+ Press [t] to toggle advanced mode (Currently Off)
+
+Use the cursor to point at the VPP_BUILD_G2 line. Press the return key
+to change OFF to ON. Press "c" to regenerate build.ninja, etc.
+
+At that point "make build" or "make build-release" will build g2. And so on.
+
+Note that toggling advanced mode ["t"] gives access to substantially
+all of the cmake option, discovered directories and paths.