Documentation: dev-manual, bsp-guide, poky-ref-manual - bblayer.conf updates

Fixes [YOCTO #3176]

Several places throughout the YP manual set examples are given
for the bblayer.conf file.  For release 1.3, a bug existed that
surfaced when a user removed either the meta or meta-yocto
layer from this configuration file.  The bug has been fixed and
the ripple effect through the YP documentation set affected
several manuals.

Fixes include updating the code samples that show bblayer.conf
so that they now include the BBLAYERS_NON_REMOVABLE variable,
a new glossary entry for the variable, and an explanation of
both BBLAYER and BBLAYER_NON_REMOVABLE in the section that
talks about the bblayer.conf file.

(From yocto-docs rev: 904b9ec1cd6d823af0e92f6891fc7e434cf2e358)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/documentation/poky-ref-manual/ref-structure.xml b/documentation/poky-ref-manual/ref-structure.xml
index c2644df374..166907ceef 100644
--- a/documentation/poky-ref-manual/ref-structure.xml
+++ b/documentation/poky-ref-manual/ref-structure.xml
@@ -247,11 +247,20 @@
         <title><filename>build/conf/bblayers.conf</filename></title>
 
         <para>
-            This file defines layers, which is a directory tree, traversed (or walked) by BitBake. 
+            This file defines layers, which are directory trees, traversed (or walked) by BitBake.
             If <filename>bblayers.conf</filename> 
             is not present, it is created from <filename>bblayers.conf.sample</filename> when 
             you <filename>source</filename> the environment setup script.
         </para>
+
+        <para>
+            The <filename>bblayers.conf</filename> file uses the
+            <link linkend='var-BBLAYERS'><filename>BBLAYERS</filename></link> variable to
+            list the layers BitBake tries to find.
+            The file uses the
+            <link linkend='var-BBLAYERS_NON_REMOVABLE'><filename>BBLAYERS_NON_REMOVABLE</filename></link>
+            variable to list layers that must not be removed.
+        </para>
     </section>
 
     <section id='structure-build-conf-sanity_info'>