docs: better docs, mv doxygen to sphinx

This patch refactors the VPP sphinx docs
in order to make it easier to consume
for external readers as well as VPP developers.

It also makes sphinx the single source
of documentation, which simplifies maintenance
and operation.

Most important updates are:

- reformat the existing documentation as rst
- split RELEASE.md and move it into separate rst files
- remove section 'events'
- remove section 'archive'
- remove section 'related projects'
- remove section 'feature by release'
- remove section 'Various links'
- make (Configuration reference, CLI docs,
  developer docs) top level items in the list
- move 'Use Cases' as part of 'About VPP'
- move 'Troubleshooting' as part of 'Getting Started'
- move test framework docs into 'Developer Documentation'
- add a 'Contributing' section for gerrit,
  docs and other contributer related infos
- deprecate doxygen and test-docs targets
- redirect the "make doxygen" target to "make docs"

Type: refactor

Change-Id: I552a5645d5b7964d547f99b1336e2ac24e7c209f
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>

1 files changed, 353 insertions, 0 deletions

diff --git a/docs/developer/corearchitecture/buildsystem/buildrootmakefile.rst b/docs/developer/corearchitecture/buildsystem/buildrootmakefile.rst
new file mode 100644
index 00000000000..1eb4e6b5301
--- /dev/null
+++ b/docs/developer/corearchitecture/buildsystem/buildrootmakefile.rst
@@ -0,0 +1,353 @@
+Introduction to build-root/Makefile
+===================================
+
+The vpp build system consists of a top-level Makefile, a data-driven
+build-root/Makefile, and a set of makefile fragments. The various parts
+come together as the result of a set of well-thought-out conventions.
+
+This section describes build-root/Makefile in some detail.
+
+Repository Groups and Source Paths
+----------------------------------
+
+Current vpp workspaces comprise a single repository group. The file
+.../build-root/build-config.mk defines a key variable called
+SOURCE\_PATH. The SOURCE\_PATH variable names the set of repository
+groups. At the moment, there is only one repository group.
+
+Single pass build system, dependencies and components
+-----------------------------------------------------
+
+The vpp build system caters to components built with GNU autoconf /
+automake. Adding such components is a simple process. Dealing with
+components which use BSD-style raw Makefiles is a more difficult.
+Dealing with toolchain components such as gcc, glibc, and binutils can
+be considerably more complicated.
+
+The vpp build system is a **single-pass** build system. A partial order
+must exist for any set of components: the set of (a before b) tuples
+must resolve to an ordered list. If you create a circular dependency of
+the form; (a,b) (b,c) (c,a), gmake will try to build the target list,
+but there’s a 0.0% chance that the results will be pleasant. Cut-n-paste
+mistakes in .../build-data/packages/.mk can produce confusing failures.
+
+In a single-pass build system, it’s best to separate libraries and
+applications which instantiate them. For example, if vpp depends on
+libfoo.a, and myapp depends on both vpp and libfoo.a, it's best to place
+libfoo.a and myapp in separate components. The build system will build
+libfoo.a, vpp, and then (as a separate component) myapp. If you try to
+build libfoo.a and myapp from the same component, it won’t work.
+
+If you absolutely, positively insist on having myapp and libfoo.a in the
+same source tree, you can create a pseudo-component in a separate .mk
+file in the .../build-data/packages/ directory. Define the code
+phoneycomponent\_source = realcomponent, and provide manual
+configure/build/install targets.
+
+Separate components for myapp, libfoo.a, and vpp is the best and easiest
+solution. However, the “mumble\_source = realsource” degree of freedom
+exists to solve intractable circular dependencies, such as: to build
+gcc-bootstrap, followed by glibc, followed by “real” gcc/g++ [which
+depends on glibc too].
+
+.../build-root
+--------------
+
+The .../build-root directory contains the repository group specification
+build-config.mk, the main Makefile, and the system-wide set of
+autoconf/automake variable overrides in config.site. We'll describe
+these files in some detail. To be clear about expectations: the main
+Makefile and config.site file are subtle and complex. It's unlikely that
+you'll need or want to modify them. Poorly planned changes in either
+place typically cause bugs that are difficult to solve.
+
+.../build-root/build-config.mk
+------------------------------
+
+As described above, the build-config.mk file is straightforward: it sets
+the make variable SOURCE\_PATH to a list of repository group absolute
+paths.
+
+The SOURCE\_PATH variable If you choose to move a workspace, make sure
+to modify the paths defined by the SOURCE\_PATH variable. Those paths
+need to match changes you make in the workspace paths. For example, if
+you place the vpp directory in the workspace of a user named jsmith, you
+might change the SOURCE\_PATH to:
+
+SOURCE\_PATH = /home/jsmithuser/workspace/vpp
+
+The "out of the box" setting should work 99.5% of the time:
+
+::
+
+        SOURCE_PATH = $(CURDIR)/..
+
+.../vpp/build-root/Makefile
+---------------------------
+
+The main Makefile is complex in a number of dimensions. If you think you
+need to modify it, it's a good idea to do some research, or ask for
+advice before you change it.
+
+The main Makefile was organized and designed to provide the following
+characteristics: excellent performance, accurate dependency processing,
+cache enablement, timestamp optimizations, git integration,
+extensibility, builds with cross-compilation tool chains, and builds
+with embedded Linux distributions.
+
+If you really need to do so, you can build double-cross tools with it,
+with a minimum amount of fuss. For example, you could: compile gdb on
+x86\_64, to run on PowerPC, to debug the Xtensa instruction set.
+
+The PLATFORM variable
+---------------------
+
+The PLATFORM make/environment variable controls a number of important
+characteristics, primarily:
+
+-  CPU architecture
+-  The list of images to build.
+
+With respect to .../build-root/Makefile, the list of images to build is
+specified by the target. For example:
+
+::
+
+       make PLATFORM=vpp TAG=vpp_debug install-deb
+
+builds vpp debug Debian packages.
+
+The main Makefile interprets $PLATFORM by attempting to "-include" the
+file /build-data/platforms.mk:
+
+::
+
+        $(foreach d,$(FULL_SOURCE_PATH), \
+          $(eval -include $(d)/platforms.mk))
+
+By convention, we don't define **platforms** in the
+...//build-data/platforms.mk file.
+
+In the vpp case, we search for platform definition makefile fragments in
+.../vpp/build-data/platforms.mk, as follows:
+
+::
+
+        $(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS), \
+             $(eval -include $(d)/platforms/*.mk))
+
+With vpp, which uses the "vpp" platform as discussed above, we end up
+"-include"-ing .../vpp/build-data/platforms/vpp.mk.
+
+The platform-specific .mk fragment
+----------------------------------
+
+Here are the contents of .../build-data/platforms/vpp.mk:
+
+::
+
+        MACHINE=$(shell uname -m)
+
+        vpp_arch = native
+        ifeq ($(TARGET_PLATFORM),thunderx)
+        vpp_dpdk_target = arm64-thunderx-linuxapp-gcc
+        endif
+        vpp_native_tools = vppapigen
+
+        vpp_uses_dpdk = yes
+
+        # Uncomment to enable building unit tests
+        # vpp_enable_tests = yes
+
+        vpp_root_packages = vpp
+
+        # DPDK configuration parameters
+        # vpp_uses_dpdk_mlx4_pmd = yes
+        # vpp_uses_dpdk_mlx5_pmd = yes
+        # vpp_uses_external_dpdk = yes
+        # vpp_dpdk_inc_dir = /usr/include/dpdk
+        # vpp_dpdk_lib_dir = /usr/lib
+        # vpp_dpdk_shared_lib = yes
+
+        # Use '--without-libnuma' for non-numa aware architecture
+        # Use '--enable-dlmalloc' to use dlmalloc instead of mheap
+        vpp_configure_args_vpp = --enable-dlmalloc
+        sample-plugin_configure_args_vpp = --enable-dlmalloc
+
+        # load balancer plugin is not portable on 32 bit platform
+        ifeq ($(MACHINE),i686)
+        vpp_configure_args_vpp += --disable-lb-plugin
+        endif
+
+        vpp_debug_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG \
+            -fstack-protector-all -fPIC -Werror
+        vpp_debug_TAG_CXXFLAGS = -g -O0 -DCLIB_DEBUG \
+            -fstack-protector-all -fPIC -Werror
+        vpp_debug_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG \
+            -fstack-protector-all -fPIC -Werror
+
+        vpp_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
+        vpp_TAG_CXXFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
+        vpp_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror -pie -Wl,-z,now
+
+        vpp_clang_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
+        vpp_clang_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
+
+        vpp_gcov_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -fprofile-arcs -ftest-coverage
+        vpp_gcov_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -coverage
+
+        vpp_coverity_TAG_CFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__
+        vpp_coverity_TAG_LDFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__
+
+Note the following variable settings:
+
+-  The variable \_arch sets the CPU architecture used to build the
+   per-platform cross-compilation toolchain. With the exception of the
+   "native" architecture - used in our example - the vpp build system
+   produces cross-compiled binaries.
+
+-  The variable \_native\_tools lists the required set of self-compiled
+   build tools.
+
+-  The variable \_root\_packages lists the set of images to build when
+   specifying the target: make PLATFORM= TAG= [install-deb \|
+   install-rpm].
+
+The TAG variable
+----------------
+
+The TAG variable indirectly sets CFLAGS and LDFLAGS, as well as the
+build and install directory names in the .../vpp/build-root directory.
+See definitions above.
+
+Important targets build-root/Makefile
+-------------------------------------
+
+The main Makefile and the various makefile fragments implement the
+following user-visible targets:
+
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| Target           | ENV Variable Settings| Notes                                                                                |
+|                  |                      |                                                                                      |
++==================+======================+======================================================================================+
+| foo              |      bar             | mumble                                                                               |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| bootstrap-tools  | none                 |  Builds the set of native tools needed by the vpp build system to                    |
+|                  |                      |  build images. Example: vppapigen. In a full cross compilation case might include    |
+|                  |                      |  include "make", "git", "find", and "tar                                             |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| install-tools    | PLATFORM             | Builds the tool chain for the indicated <platform>. Not used in vpp builds           |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| distclean        | none                 | Roto-rooters everything in sight: toolchains, images, and so forth.                  |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| install-deb      | PLATFORM and TAG     | Build Debian packages comprising components listed in <platform>_root_packages,      |
+|                  |                      | using compile / link options defined by TAG.                                         |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+| install-rpm      | PLATFORM and TAG     | Build RPMs comprising components listed in <platform>_root_packages,                 |
+|                  |                      | using compile / link options defined by TAG.                                         |
++------------------+----------------------+--------------------------------------------------------------------------------------+
+
+Additional build-root/Makefile environment variable settings
+------------------------------------------------------------
+
+These variable settings may be of use:
+
++----------------------+------------------------------------------------------------------------------------------------------------+
+| ENV Variable         | Notes                                                                                                      |
++======================+======================+=====================================================================================+
+| BUILD_DEBUG=vx       | Directs Makefile et al. to make a good-faith effort to show what's going on in excruciating detail.        |
+|                      | Use it as follows: "make ... BUILD_DEBUG=vx". Fairly effective in Makefile debug situations.               |
++----------------------+------------------------------------------------------------------------------------------------------------+
+| V=1                  | print detailed cc / ld command lines. Useful for discovering if -DFOO=11 is in the command line or not     |
++----------------------+------------------------------------------------------------------------------------------------------------+
+| CC=mygcc             | Override the configured C-compiler                                                                         |
++----------------------+------------------------------------------------------------------------------------------------------------+
+
+.../build-root/config.site
+--------------------------
+
+The contents of .../build-root/config.site override individual autoconf /
+automake default variable settings. Here are a few sample settings related to
+building a full toolchain:
+
+::
+
+    # glibc needs these setting for cross compiling
+    libc_cv_forced_unwind=yes
+    libc_cv_c_cleanup=yes
+    libc_cv_ssp=no
+
+Determining the set of variables which need to be overridden, and the
+override values is a matter of trial and error. It should be
+unnecessary to modify this file for use with fd.io vpp.
+
+.../build-data/platforms.mk
+---------------------------
+
+Each repo group includes the platforms.mk file, which is included by
+the main Makefile. The vpp/build-data/platforms.mk file is not terribly
+complex. As of this writing, .../build-data/platforms.mk file accomplishes two
+tasks.
+
+First, it includes vpp/build-data/platforms/\*.mk:
+
+::
+
+    # Pick up per-platform makefile fragments
+    $(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS),	\
+      $(eval -include $(d)/platforms/*.mk))
+
+This collects the set of platform definition makefile fragments, as discussed above.
+
+Second, platforms.mk implements the user-visible "install-deb" target.
+
+.../build-data/packages/\*.mk
+-----------------------------
+
+Each component needs a makefile fragment in order for the build system
+to recognize it. The per-component makefile fragments vary
+considerably in complexity. For a component built with GNU autoconf /
+automake which does not depend on other components, the make fragment
+can be empty. See .../build-data/packages/vpp.mk for an uncomplicated
+but fully realistic example.
+
+Here are some of the important variable settings in per-component makefile fragments:
+
++----------------------+------------------------------------------------------------------------------------------------------------+
+| Variable             | Notes                                                                                                      |
++======================+======================+=====================================================================================+
+| xxx_configure_depend |  Lists the set of component build dependencies for the xxx component. In plain English: don't try to       |
+|                      |  configure this component until you've successfully built the indicated targets. Almost always,            |
+|                      |  xxx_configure_depend will list a set of "yyy-install" targets. Note the pattern:                          |
+|                      |  "variable names contain underscores, make target names contain hyphens"                                   |
++----------------------+------------------------------------------------------------------------------------------------------------+
+| xxx_configure_args   | (optional) Lists any additional arguments to pass to the xxx component "configure" script.                 |
+|                      | The main Makefile %-configure rule adds the required settings for --libdir, --prefix, and                  |
+|                      | --host (when cross-compiling)                                                                              |
++----------------------+------------------------------------------------------------------------------------------------------------+
+| xxx_CPPFLAGS         | Adds -I stanzas to CPPFLAGS for components upon which xxx depends.                                         |
+|                      | Almost invariably "xxx_CPPFLAGS = $(call installed_includes_fn, dep1 dep2 dep3)", where dep1, dep2, and    |
+|                      | dep3 are listed in xxx_configure_depend. It is bad practice to set "-g -O3" here. Those settings           |
+|                      | belong in a TAG.                                                                                           |
++----------------------+------------------------------------------------------------------------------------------------------------+
+| xxx_LDFLAGS          | Adds -Wl,-rpath -Wl,depN stanzas to LDFLAGS for components upon which xxx depends.                         |
+|                      | Almost invariably "xxx_LDFLAGS = $(call installed_lib_fn, dep1 dep2 dep3)", where dep1, dep2, and          |
+|                      | dep3 are listed in xxx_configure_depend. It is bad manners to set "-liberty-or-death" here.                |
+|                      | Those settings belong in Makefile.am.                                                                      |
++----------------------+------------------------------------------------------------------------------------------------------------+
+
+When dealing with "irritating" components built with raw Makefiles
+which only work when building in the source tree, we use a specific
+strategy in the xxx.mk file.
+
+The strategy is simple for those components: We copy the source tree
+into .../vpp/build-root/build-xxx. This works, but completely defeats
+dependency processing. This strategy is acceptable only for 3rd party
+software which won't need extensive (or preferably any) modifications.
+
+Take a look at .../vpp/build-data/packages/dpdk.mk. When invoked, the
+dpdk_configure variable copies source code into $(PACKAGE_BUILD_DIR),
+and performs the BSD equivalent of "autoreconf -i -f" to configure the
+build area. The rest of the file is similar: a bunch of hand-rolled
+glue code which manages to make the dpdk act like a good vpp build
+citizen even though it is not.