Re: [dpdk-dev] [PATCH 2/8] doc: add building with meson to linux GSG

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Nov 25, 2019 at 01:19:13PM +0000, Burakov, Anatoly wrote:
> On 22-Nov-19 4:03 PM, Bruce Richardson wrote:
> > Add instructions on building DPDK and using the pkg-config file to the
> > linux GSG.
> > 
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> >   doc/guides/linux_gsg/build_dpdk.rst | 94 +++++++++++++++++++++++++++--
> >   1 file changed, 90 insertions(+), 4 deletions(-)
> > 
> > diff --git a/doc/guides/linux_gsg/build_dpdk.rst b/doc/guides/linux_gsg/build_dpdk.rst
> > index 7c0329fcc..5710effbc 100644
> > --- a/doc/guides/linux_gsg/build_dpdk.rst
> > +++ b/doc/guides/linux_gsg/build_dpdk.rst
> > @@ -11,8 +11,8 @@ Compiling the DPDK Target from Source
> >       Parts of this process can also be done using the setup script described in
> >       the :ref:`linux_setup_script` section of this document.
> > -Install the DPDK and Browse Sources
> > ------------------------------------
> > +Uncompress DPDK and Browse Sources
> > +----------------------------------
> >   First, uncompress the archive and move to the uncompressed DPDK source directory:
> > @@ -33,8 +33,94 @@ The DPDK is composed of several directories:
> >   *   config, buildtools, mk: Framework-related makefiles, scripts and configuration
> > -Installation of DPDK Target Environments
> > -----------------------------------------
> > +Compiling and Installing DPDK System-wide
> > +-----------------------------------------
> > +
> > +DPDK can be configured, built and installed on your system using the tools
> > +``meson`` and ``ninja``.
> > +
> > +.. note::
> > +
> > +  The older makefile-based build system used in older DPDK releases is
> > +  still present and it's use is described in section
> 
> *its
> 
Thanks.

> > +  `Installation of DPDK Target Environment using Make`_.
> > +
> > +DPDK Configuration
> > +~~~~~~~~~~~~~~~~~~
> > +
> > +To configure a DPDK build use:
> > +
> > +.. code-block:: console
> > +
> > +     meson <options> build
> > +
> > +where "build" is the desired output build directory, and "<options>" can be
> > +empty or one of a number of meson or DPDK-specific build options, described
> > +later in this section. The configuration process will finish with a summary
> > +of what DPDK libraries and drivers are to be built and installed, and for
> > +each item disabled, a reason why that is the case. This information can be
> > +used, for example, to identify any missing required packages for a driver.
> > +
> > +Once configured, to build and then install DPDK system-wide use:
> > +
> > +.. code-block:: console
> > +
> > +        cd build
> > +        ninja
> > +        ninja install
> > +
> > +Adjusting Build Options
> > +~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +DPDK has a number of options that can be adjusted as part of the build configuration process.
> > +These options can be listed by running ``meson configure`` inside a configured build folder.
> > +Many of these options come from the "meson" tool itself and can be seen documented on the
> > +`Meson Website <https://mesonbuild.com/Builtin-options.html>`_.
> > +
> > +For example, to change the build-type from the default, "debugoptimized",
> > +to a regular "debug" build, you can either:
> > +
> > +* pass ``-Dbuildtype=debug`` or ``--buildtype=debug`` to meson when configuring the build folder initially
> > +
> > +* run ``meson configure -Dbuildtype=debug`` inside the build folder after the initial meson run.
> > +
> > +Other options are specific to the DPDK project but can be adjusted similarly.
> > +To set the "max_lcores" value to 256, for example, you can either:
> > +
> > +* pass ``-Dmax_lcores=256`` to meson when configuring the build folder initially
> > +
> > +* run ``meson configure -Dmax_lcores=256`` inside the build folder after the initial meson run.
> 
> This *very* welcome. It's a pity it's not possible to run these /before/
> creating a build directory, but i'll take it!
> 

Can you clarify what you mean here? Passing max_lcores to the initial meson
run isn't sufficient, you think?

> A common source of confusion for people building example apps with meson is
> that, unlike with make, you don't build DPDK first and then build examples,
> you build them all at once. Perhaps it would be worth calling this out
> explicitly?
> 
I was actually thinking that that functionality was primarily targeted at
developers rather than at end users. However, I can include the -Dexamples
flag for reference here for people.

> Also, kinda unrelated to this, but can we add an "all" target that actually
> fails if one of the examples doesn't build? IIRC currently it'll just skip
> through any that don't build, which is not ideal for quick compile testing.
> I mean, obviously apps that don't have their dependencies met shouldn't be
> attempted, but if any /buildable/ examples fail to build, i think there
> should be a way to communicate this without having to explicitly call out
> all example apps in the -Dexamples option. (if it currently works that way,
> disregard!)

This should indeed be the way it currently works. The examples to be built
depends upon the detected dependencies at configure time, but thereafter on
compile, ninja knows nothing about examples or otherwise, it just sees code
to be compiled and linked and should error out if anything fails. If this
is not the case, it's a bug we need to fix.

> 
> > +
> > +Building Applications Using Installed DPDK
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +When installed system-wide, DPDK provides a pkg-config file ``libdpdk.pc`` for applications to query as part of their build.
> > +It's recommended that the pkg-config file be used, rather than hard-coding the parameters (cflags/ldflags)
> > +for DPDK into the application build process.
> > +
> > +An example of how to query and use the pkg-config file can be found in the ``Makefile`` of each of the example applications included with DPDK.
> > +A simplified example snippet is shown below, where the target binary name has been stored in the variable ``$(APP)``
> > +and the sources for that build are stored in ``$(SRCS-y)``.
> > +
> > +.. code-block:: makefile
> > +
> > +        PKGCONF = pkg-config
> > +
> > +        CFLAGS += -O3 $(shell $(PKGCONF) --cflags libdpdk)
> > +        LDFLAGS += $(shell $(PKGCONF) --libs libdpdk)
> > +
> > +        $(APP): $(SRCS-y) Makefile
> > +                $(CC) $(CFLAGS) $(SRCS-y) -o $@ $(LDFLAGS)
> 
> What about a meson-based example?
> 
I didn't think such a thing would be work including, since the number of
end-user apps using meson is likely fairly small. We'd also then need to
include an example using cmake or other build systems too, for
completeness.

> Also, i think it's worth calling out the fact that (at least as far as i
> know) it's not possible to use DPDK built with meson without installing it.
> With make, it's possible to have RTE_SDK/RTE_TARGET defined, and that will
> work without installing DPDK systemwide, but not with meson.
> 
It's probably possible, but I've never looked into the details of it. I'll
add a note requiring installation of DPDK for linking to the documentation.

> > +
> > +
> > +Installation of DPDK Target Environment using Make
> > +--------------------------------------------------
> > +
> > +.. note::
> > +
> > +   The building of DPDK using make will be deprecated in a future release. It
> > +   is therefore recommended that DPDK installation is done using meson and
> > +   ninja as described above.
> >   The format of a DPDK target is::
> > 
>