* Add documentation of LAYERVERSION, LAYERDEPENDS and new layer priority
  behaviour
* Improve some wording

Signed-off-by: Paul Eggleton <[email protected]>
---
 documentation/poky-ref-manual/ref-variables.xml |   46 +++++++++++++++++++---
 1 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/documentation/poky-ref-manual/ref-variables.xml 
b/documentation/poky-ref-manual/ref-variables.xml
index eab3bda..b6bf97a 100644
--- a/documentation/poky-ref-manual/ref-variables.xml
+++ b/documentation/poky-ref-manual/ref-variables.xml
@@ -72,22 +72,24 @@
 
         <glossentry 
id='var-BBFILE_COLLECTIONS'><glossterm>BBFILE_COLLECTIONS</glossterm>
             <glossdef>
-                <para>Identifies layer-specific bbfiles, which contain recipes 
used by BitBake to build software.
-                    The variable is appended with a layer name.</para>
+                <para>Lists the names of configured layers. These names are 
used to find the other BBFILE_*
+                    variables. Typically each layer will append its name to 
this variable in its
+                    <filename>conf/layer.conf</filename> file.
+                </para>
             </glossdef>
         </glossentry>
 
         <glossentry 
id='var-BBFILE_PATTERN'><glossterm>BBFILE_PATTERN</glossterm>
             <glossdef>
                 <para>Variable that expands to match files from BBFILES in a 
particular layer.  BBFILE_PATTERN 
-                    is used in the <filename>conf/layer.conf</filename> file 
and must contain the name of the 
-                    specific layer (e.g. BBFILE_PATTERN_emenlow).</para>
+                    is used in the <filename>conf/layer.conf</filename> file 
and must be suffixed with the name
+                    of the specific layer (e.g. BBFILE_PATTERN_emenlow).</para>
             </glossdef>
         </glossentry>
 
         <glossentry 
id='var-BBFILE_PRIORITY'><glossterm>BBFILE_PRIORITY</glossterm>
             <glossdef>
-                <para>Assigns different priorities to recipe files in 
different layers.</para>
+                <para>Assigns the priority for recipe files in each 
layer.</para>
                 <para>This variable is useful in situations where the same 
package appears in
                     more than one layer. 
                     Setting BBFILE_PRIORITY allows you to prioritize a
@@ -102,13 +104,20 @@
                     precedence. 
                     For example, the value 6 has a higher precedence than the
                     value 5. 
-                    By default, the BBFILE_PRIORITY variable is set to the 
value 5.</para>
+                    If not specified, the BBFILE_PRIORITY variable is set 
based on layer
+                    dependencies (see LAYERDEPENDS below). Tdefault priority 
if unspecified
+                    for a layer with no dependencies is the lowest defined 
priority + 1
+                    (or 1 if no priorities are defined).</para>
+                <tip>
+                    You can use the command "bitbake-layers show_layers" to 
list
+                    all configured layers along with their priorities.
+                </tip>
             </glossdef>
         </glossentry>
 
         <glossentry id='var-BBFILES'><glossterm>BBFILES</glossterm>
             <glossdef>
-                <para>List of recipes used by BitBake to build software</para>
+                <para>List of recipe files used by BitBake to build 
software</para>
             </glossdef>
         </glossentry>
 
@@ -520,6 +529,19 @@ recipes-graphics/xorg-font/fiont-alias_1.0.2.bb:PR - 
"$(INC_PR).0"
 
     <glossdiv id='var-glossary-l'><title>L</title>
 
+        <glossentry id='var-LAYERDEPENDS'><glossterm>LAYERDEPENDS</glossterm>
+            <glossdef>
+                <para>Lists the layers that this recipe depends upon, 
separated by spaces.
+                    Optionally a specific layer version may be specified for a 
dependency
+                    by adding it to the end of the layer name with a colon, 
e.g. "anotherlayer:3"
+                    (to be compared against LAYERVERSION_anotherlayer in this 
example).
+                    An error will be produced if any dependency is missing or
+                    the version numbers do not match exactly (if specified).
+                    This variable is used in the 
<filename>conf/layer.conf</filename> file 
+                    and must be suffixed with the name of the specific layer 
(e.g. 
+                    LAYERDEPENDS_mylayer).</para>
+            </glossdef>
+        </glossentry>
         <glossentry id='var-LAYERDIR'><glossterm>LAYERDIR</glossterm>
             <glossdef>
                 <para>When used inside a layer.conf gives the path of the
@@ -529,6 +551,16 @@ recipes-graphics/xorg-font/fiont-alias_1.0.2.bb:PR - 
"$(INC_PR).0"
                 giving the wrong value.</para>
             </glossdef>
         </glossentry>
+        <glossentry id='var-LAYERVERSION'><glossterm>LAYERVERSION</glossterm>
+            <glossdef>
+                <para>Optionally specifies the version of a layer as a single 
number.
+                    This may be used within LAYERDEPENDS for another layer in 
order to
+                    depend on a specific version of the layer.
+                    This variable is used in the 
<filename>conf/layer.conf</filename> file 
+                    and must be suffixed with the name of the specific layer 
(e.g.
+                    LAYERVERSION_mylayer).</para>
+            </glossdef>
+        </glossentry>
         <glossentry id='var-LICENSE'><glossterm>LICENSE</glossterm>
             <glossdef>
                 <para>List of package source licenses.</para>
-- 
1.7.4.1

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