[dpdk-dev] [PATCH v2 3/3] doc: add notes on overriding extra config values

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

Since it's possible to tweak the DPDK build a little further using CFLAGS,
we note that in the documentation.

Suggested-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 doc/guides/linux_gsg/build_dpdk.rst       | 8 ++++++++
 doc/guides/prog_guide/build-sdk-meson.rst | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/doc/guides/linux_gsg/build_dpdk.rst b/doc/guides/linux_gsg/build_dpdk.rst
index c536e354e..9c242069e 100644
--- a/doc/guides/linux_gsg/build_dpdk.rst
+++ b/doc/guides/linux_gsg/build_dpdk.rst
@@ -117,6 +117,14 @@ dependencies are met on the current system are built.
 When `-Dexamples=all` is set as a meson option, meson will check each example application to see if it can be built,
 and add all which can be built to the list of tasks in the ninja build configuration file.
 
+.. note::
+
+    A number of buildtime constants are present in DPDK, listed in file ``config/rte_config.h``.
+    While these should not normally need to be changed,
+    they can be overridden by setting the new value of the constant in the ``CFLAGS`` environment variable,
+    or via ``c_args`` meson parameter.
+    For example: ``meson configure -Dc_args="-DRTE_PKTMBUF_HEADROOM=256"``
+
 Building Applications Using Installed DPDK
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/doc/guides/prog_guide/build-sdk-meson.rst b/doc/guides/prog_guide/build-sdk-meson.rst
index 44d1cafdf..3838871a3 100644
--- a/doc/guides/prog_guide/build-sdk-meson.rst
+++ b/doc/guides/prog_guide/build-sdk-meson.rst
@@ -68,6 +68,14 @@ built into meson, while others, such as ``max_lcores``, or the list of
 examples to build, are DPDK-specific. To have a list of all options
 available run ``meson configure`` in the build directory.
 
+.. note::
+
+    A number of buildtime constants are present in DPDK, listed in file ``config/rte_config.h``.
+    While these should not normally need to be changed,
+    they can be overridden by setting the new value of the constant in the ``CFLAGS`` environment variable,
+    or via ``c_args`` meson parameter.
+    For example: ``meson configure -Dc_args="-DRTE_PKTMBUF_HEADROOM=256"``
+
 Examples of adjusting the defaults when doing initial meson configuration.
 Project-specific options are passed used -Doption=value::
 
-- 
2.25.1