build: print list of disabled components

When configuring with meson we print out a list of enabled components, but
it is also useful to list out the disabled components and the reasons why.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Luca Boccassi <bluca@debian.org>

doc/guides/contributing/coding_style.rst

@@ -852,12 +852,15 @@ allow_experimental_apis
 build
 	**Default Value = true**
 	Used to optionally compile a library, based on its dependencies or
-	environment. A simple example of use would be:
+	environment. When set to "false" the ``reason`` value, explained below, should
+	also be set to explain to the user why the component is not being built.
+	A simple example of use would be:
 
 .. code-block:: python
 
 	if not is_linux
 	        build = false
+	        reason = 'only supported on Linux'
 	endif
 
 
@@ -938,6 +941,13 @@ objs
 	objects that were compiled up as part of another target given in the
 	included library ``meson.build`` file.
 
+reason
+	**Default Value = '<unknown reason>'**.
+	This variable should be used when a library is not to be built i.e. when
+	``build`` is set to "false", to specify the reason why a library will not be
+	built. For missing dependencies this should be of the form
+	``'missing dependency, "libname"'``.
+
 version
 	**Default Value = 1**.
 	Specifies the ABI version of the library, and is used as the major
@@ -991,6 +1001,9 @@ pkgconfig_extra_libs
 	using static libraries. Anything added here will be appended to the end
 	of the ``pkgconfig --libs`` output.
 
+reason
+	As above.
+
 sources [mandatory]
 	As above
 

drivers/meson.build

@@ -37,6 +37,7 @@ foreach class:dpdk_driver_classes
 
 		# set up empty variables used for build
 		build = true # set to false to disable, e.g. missing deps
+		reason = '<unknown reason>' # set if build == false to explain
 		name = drv
 		version = 1
 		allow_experimental_apis = false
@@ -58,7 +59,16 @@ foreach class:dpdk_driver_classes
 		# pull in driver directory which should assign to each of the above
 		subdir(drv_path)
 
-		if build
+		if not build
+			# some driver directories are placeholders which
+			# are never built, so we allow suppression of the
+			# component disable printout in those cases
+			if reason != ''
+				dpdk_drvs_disabled += drv_path
+				set_variable(drv_path.underscorify() +
+						'_disable_reason', reason)
+			endif
+		else
 			class_drivers += name
 
 			dpdk_conf.set(config_flag_fmt.format(name.to_upper()),1)

lib/meson.build

@@ -43,6 +43,7 @@ enabled_libs = [] # used to print summary at the end
 
 foreach l:libraries
 	build = true
+	reason = '<unknown reason>' # set if build == false to explain why
 	name = l
 	version = 1
 	allow_experimental_apis = false
@@ -65,7 +66,10 @@ foreach l:libraries
 	dir_name = 'librte_' + l
 	subdir(dir_name)
 
-	if build
+	if not build
+		dpdk_libs_disabled += name
+		set_variable(name.underscorify() + '_disable_reason', reason)
+	else
 		enabled_libs += name
 		dpdk_conf.set('RTE_LIBRTE_' + name.to_upper(), 1)
 		install_headers(headers)

meson.build

@@ -20,6 +20,8 @@ dpdk_driver_classes = []
 dpdk_drivers = []
 dpdk_extra_ldflags = []
 dpdk_app_link_libraries = []
+dpdk_libs_disabled = []
+dpdk_drvs_disabled = []
 
 # configure the build, and make sure configs here and in config folder are
 # able to be included in any file. We also store a global array of include dirs
@@ -112,3 +114,16 @@ foreach class:dpdk_driver_classes
 	endforeach
 endforeach
 message(output_message + '\n')
+
+output_message = '\n=================\nContent Skipped\n=================\n'
+output_message += '\nlibs:\n\t'
+foreach lib:dpdk_libs_disabled
+	reason = get_variable(lib.underscorify() + '_disable_reason')
+	output_message += lib + ':\t' + reason + '\n\t'
+endforeach
+output_message += '\ndrivers:\n\t'
+foreach drv:dpdk_drvs_disabled
+	reason = get_variable(drv.underscorify() + '_disable_reason')
+	output_message += drv + ':\t' + reason + '\n\t'
+endforeach
+message(output_message + '\n')