[PATCH 4/4] native.bbclass: Use fixed DISTRO_FEATURES

[Jussi Kukkonen <jussi.kukkonen@intel.com>]

There seems to be no advantage to letting distro features affect
native builds. There is a significant disadvantage: a change to
DISTRO_FEATURES will trigger a lot of unnecessary native tasks. In a
test like this:
  $ bitbake core-image-minimal
  # append " systemd" to DISTRO_FEATURES
  $ bitbake core-image-minimal
The latter build takes 44 minutes (28%) of cpu-time less with this
patch (skipping 135 native tasks). Sadly wall clock time was not
affected as glibc remains the bottleneck.

Set DISTRO_FEATURES to a fixed value for native recipes to avoid the
unnecessary tasks: currently the default value is empty.

Do the variable setting in native_virtclass_handler() because otherwise
it could still be overridden by appends and the feature backfilling.
Shuffle the early returns so DISTRO_FEATURES gets set as long as
the packagename ends with "-native".

Signed-off-by: Jussi Kukkonen <jussi.kukkonen@intel.com>
---
 meta/classes/native.bbclass | 12 ++++++++----
 meta/conf/bitbake.conf      |  2 ++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/meta/classes/native.bbclass b/meta/classes/native.bbclass
index 1919fbc..fbca4c6 100644
--- a/meta/classes/native.bbclass
+++ b/meta/classes/native.bbclass
@@ -121,14 +121,18 @@ PATH_prepend = "${COREBASE}/scripts/native-intercept:"
 SSTATE_SCAN_CMD ?= "${SSTATE_SCAN_CMD_NATIVE}"
 
 python native_virtclass_handler () {
-    classextend = e.data.getVar('BBCLASSEXTEND') or ""
-    if "native" not in classextend:
-        return
-
     pn = e.data.getVar("PN")
     if not pn.endswith("-native"):
         return
 
+    # Set features here to prevent appends and distro features backfill
+    # from modifying native distro features
+    d.setVar("DISTRO_FEATURES", "${NATIVE_DISTRO_FEATURES}")
+
+    classextend = e.data.getVar('BBCLASSEXTEND') or ""
+    if "native" not in classextend:
+        return
+
     def map_dependencies(varname, d, suffix = ""):
         if suffix:
             varname = varname + "_" + suffix
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index 5e98d45..78a3470 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -789,6 +789,8 @@ MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS ?= ""
 EXTRA_IMAGE_FEATURES ??= ""
 IMAGE_FEATURES += "${EXTRA_IMAGE_FEATURES}"
 
+NATIVE_DISTRO_FEATURES ?= ""
+
 DISTRO_FEATURES_BACKFILL = "pulseaudio sysvinit bluez5 gobject-introspection-data ldconfig"
 MACHINE_FEATURES_BACKFILL = "rtc qemu-usermode"
 
-- 
2.1.4