[gnome-continuous-yocto/gnomeostree-3.28-rocko: 2961/8267] ref-manual: Updated build/tmp/cache/ reference section

[Emmanuele Bassi <ebassi src gnome org>]

commit ca85107b9ad5358573052b88e98665c7110288c2
Author: Scott Rifenbark <srifenbark gmail com>
Date:   Mon Oct 3 10:02:05 2016 -0700

    ref-manual: Updated build/tmp/cache/ reference section
    
    Fixes [YOCTO #10356]
    
    Expanded the general description of this directory.
    
    (From yocto-docs rev: df71fe472f9d5cb5f809706ec4218952a49d31d3)
    
    Signed-off-by: Scott Rifenbark <srifenbark gmail com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 documentation/ref-manual/ref-structure.xml |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)
---
diff --git a/documentation/ref-manual/ref-structure.xml b/documentation/ref-manual/ref-structure.xml
index 6912d3f..541a47e 100644
--- a/documentation/ref-manual/ref-structure.xml
+++ b/documentation/ref-manual/ref-structure.xml
@@ -660,9 +660,21 @@
         <title><filename>build/tmp/cache/</filename></title>
 
         <para>
-            When BitBake parses the metadata, it creates a cache file of the result that can
-            be used when subsequently running commands.
-            BitBake stores these results here on a per-machine basis.
+            When BitBake parses the metadata (recipes and configuration files),
+            it caches the results in <filename>build/tmp/cache/</filename>
+            to speed up future builds.
+            The results are stored on a per-machine basis.
+        </para>
+
+        <para>
+            During subsequent builds, BitBake checks each recipe (together
+            with, for example, any files included or appended to it) to see
+            if they have been modified.
+            Changes can be detected, for example, through file modification
+            time (mtime) changes and hashing of file contents.
+            If no changes to the file are detected, then the parsed result
+            stored in the cache is reused.
+            If the file has changed, it is reparsed.
         </para>
     </section>