[OE-core] [PATCH v3] Add new IMAGE_CLASSES variable for classes for image generation

[Matthew McClintock]

Allows us to import classes only for images and not to the global
namespace

Signed-off-by: Matthew McClintock <msm at freescale.com>
---

v2: Change IMAGE_CLASSES definition to use ?= instead of =
so it's clear we want to override this variable. This worked
before because the value in my distro.conf file overwrote
this value regardless of the fact it was set with =

v3: Move documentation to local.conf.sample.extended

 meta-yocto/conf/local.conf.sample.extended |    6 ++++++
 meta/classes/image.bbclass                 |    3 ++-
 2 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/meta-yocto/conf/local.conf.sample.extended b/meta-yocto/conf/local.conf.sample.extended
index 0c3197d..e9935ce 100644
--- a/meta-yocto/conf/local.conf.sample.extended
+++ b/meta-yocto/conf/local.conf.sample.extended
@@ -114,3 +114,9 @@
 # The network based PR service host and port
 #PRSERV_HOST = "localhost"
 #PRSERV_PORT = "8585"
+
+# Additional image generation features
+#
+# The following is a list of classes to import to use in the generation of images
+# currently an example class is image_types_uboot
+# IMAGE_CLASSES = " image_types_uboot"
diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index 05f4331..a2770a4 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -111,7 +111,8 @@ def get_devtable_list(d):
         str += " %s" % bb.which(bb.data.getVar('BBPATH', d, 1), devtable)
     return str
 
-inherit image_types
+IMAGE_CLASSES ?= "image_types"
+inherit ${IMAGE_CLASSES}
 
 IMAGE_POSTPROCESS_COMMAND ?= ""
 MACHINE_POSTPROCESS_COMMAND ?= ""
-- 
1.7.6.1