[PATCH v4 4/4] build: select optional libraries

[David Marchand <david.marchand@redhat.com>]

There is currently no way to know which libraries are optional.
Introduce a enable_libs option (close to what we have for drivers) so
that packagers or projects consuming DPDK can more easily select the
optional libraries that matter to them and disable other optional
libraries.

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
Changes since v3:
- split non related cleanup changes,
- fixed false positive complaints about disabling mandatory libs by
  building the list of always enabled libs, appending this list to
  enable_list and checking the disable side,
- updated enable/disable_libs descriptions,

Changes since v2:
- moved the IOVA check for kni build in lib/kni/meson.build,
- reworked deprecated libraries handling by only considering them when
  no enable_libs option is set. With this, no need for a default value
  in meson_options.txt, yet configurations in the CI must be adjusted,
- moved mandatory libraries check after enable/disable_libs evaluation,

---
 lib/meson.build   | 33 +++++++++++++++++++++++----------
 meson_options.txt |  4 +++-
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/lib/meson.build b/lib/meson.build
index a6e9e19b42..407769b270 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -92,17 +92,20 @@ dpdk_libs_deprecated += [
         'kni',
 ]
 
-disabled_libs = []
-opt_disabled_libs = run_command(list_dir_globs, get_option('disable_libs'),
-        check: true).stdout().split()
-foreach l:opt_disabled_libs
+disable_libs = run_command(list_dir_globs, get_option('disable_libs'), check: true).stdout().split()
+
+enable_libs = run_command(list_dir_globs, get_option('enable_libs'), check: true).stdout().split()
+if enable_libs.length() == 0
+    enable_libs += optional_libs
+endif
+
+always_enable = []
+foreach l:libraries
     if not optional_libs.contains(l)
-        warning('Cannot disable mandatory library "@0@"'.format(l))
-        continue
+        always_enable += l
     endif
-    disabled_libs += l
 endforeach
-
+enable_libs += always_enable
 
 default_cflags = machine_args
 default_cflags += ['-DALLOW_EXPERIMENTAL_API']
@@ -139,12 +142,22 @@ foreach l:libraries
     if dpdk_libs_deprecated.contains(l) and not get_option('enable_deprecated_libs')
         build = false
         reason = 'deprecated libraries disabled via build config'
-    elif disabled_libs.contains(l)
+    elif not enable_libs.contains(l)
         build = false
-        reason = 'explicitly disabled via build config'
+        reason = 'not in enabled libraries build config'
         if dpdk_libs_deprecated.contains(l)
             reason += ' (deprecated lib)'
         endif
+    elif disable_libs.contains(l)
+        if always_enable.contains(l)
+            warning('Cannot disable mandatory library "@0@"'.format(l))
+        else
+            build = false
+            reason = 'explicitly disabled via build config'
+            if dpdk_libs_deprecated.contains(l)
+                reason += ' (deprecated lib)'
+            endif
+        endif
     endif
 
     if build
diff --git a/meson_options.txt b/meson_options.txt
index f959015e46..9951563146 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -11,7 +11,7 @@ option('disable_apps', type: 'string', value: '', description:
 option('disable_drivers', type: 'string', value: '', description:
        'Comma-separated list of drivers to explicitly disable.')
 option('disable_libs', type: 'string', value: '', description:
-       'Comma-separated list of libraries to explicitly disable. [NOTE: not all libs can be disabled]')
+       'Comma-separated list of optional libraries to explicitly disable. [NOTE: mandatory libs cannot be disabled]')
 option('drivers_install_subdir', type: 'string', value: 'dpdk/pmds-<VERSION>', description:
        'Subdirectory of libdir where to install PMDs. Defaults to using a versioned subdirectory.')
 option('enable_docs', type: 'boolean', value: false, description:
@@ -26,6 +26,8 @@ option('enable_driver_sdk', type: 'boolean', value: false, description:
        'Install headers to build drivers.')
 option('enable_kmods', type: 'boolean', value: false, description:
        'build kernel modules')
+option('enable_libs', type: 'string', value: '', description:
+       'Comma-separated list of optional libraries to explicitly enable. [NOTE: mandatory libs are always enabled]')
 option('examples', type: 'string', value: '', description:
        'Comma-separated list of examples to build by default')
 option('ibverbs_link', type: 'combo', choices : ['static', 'shared', 'dlopen'], value: 'shared', description:
-- 
2.40.1