add 'yocto-layer-example'

This is a first attemp to create a new slideset for day2 of yocto-trainig.

The slideset is based on 'yocto-advanced' but with integration of
'meta-schulung' explanations.

I used a slightly modified version of 'meta-schulung'. The following changes
are currently not available in git:

I don't use linux-yocto in meta-schulung, but use an own kernel-recipe and
integrate the RT-PREEMPT patch.

wic: i can't see the need for the second partition and the need for huge files
in the kconfig. It works for me by adding ' --align 1024 ' to the wic setup.
I decided to use ext2 instead of ext4.

I renamed the rootfs.bb file into schulung-base.bb

I use the u-boot recipe from poky. However i don't use u-boot for anything atm.
  But bootloader is on our agenda..

Signed-off-by: Manuel Traut <manut@linutronix.de>

1 files changed, 84 insertions, 0 deletions

diff --git a/distribution/yocto-example-layer/yocto-layers.tex b/distribution/yocto-example-layer/yocto-layers.tex
new file mode 100644
index 0000000..a9eebb6
--- /dev/null
+++ b/distribution/yocto-example-layer/yocto-layers.tex
@@ -0,0 +1,84 @@
+\subsection{Yocto Layers}
+
+\begin{frame}
+\frametitle{bitbake-layers}
+is useful to debug relations between different layers, options are:
+\begin{description}
+\item [show-layers] shows the current configured layers
+\item [show-recipes] lists available recipes and the layers that provide them.
+\item [show-overlayed] lists overlayed recipes
+\item [show-appends] lists .bbappend files
+        and the recipe files to which they apply
+\item [show-cross-depends] lists dependency relationships
+        between recipes that cross layer boundaries
+\item [flatten] flattens the layer configuration
+        into a separate output directory.
+\end{description}
+\end{frame}
+
+\begin{frame}[fragile]
+\frametitle{Create and use own layer}
+\begin{lstlisting}
+$ cd ~/poky
+$ . ./oe-init-build-env build-schulung
+$ cd ..
+$ bitbake-layers create-layer -p 10 meta-schulung
+NOTE: Starting bitbake server...
+Add your new layer with 'bitbake-layers add-layer meta-schulung'
+$ cd build-schulung
+$ bitbake-layers add-layer ../meta-schulung
+NOTE: Starting bitbake server...
+\end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+\frametitle{Folder layout}
+\begin{verbatim}
+meta-schulung
++ conf
+|  + layer.conf
++ classes
+|  + class1.bbclass
+|  + class2.bbclass
++ recipes-category1
+|  + package-1
+|      + package-1.bb
+|  + package-2
+|      + package-2.bb
++ recipes-category2
+| ..
+\end{verbatim}
+\end{frame}
+
+\begin{frame}[fragile]
+\frametitle{meta-*/conf/layer.conf}
+each layer needs a configuration file
+\begin{itemize}
+\item add conf and class directories to BBPATH
+\begin{verbatim}BBPATH =. "${LAYERDIR}"\end{verbatim}
+\item add recipe directories to BBFILES
+\begin{verbatim}BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
+        ${LAYERDIR}/recipes-*/*/*.bbappend"\end{verbatim}
+\item add layer name to BBFILE\_COLLECTIONS
+\begin{verbatim}BBFILE_COLLECTIONS += "mylayer"\end{verbatim}
+\item set root of the layer
+\begin{verbatim}BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"\end{verbatim}
+\item set default priority of the layer
+\begin{verbatim}BBFILE_PRIORITY_mylayer = "5"\end{verbatim}
+\item set version of layer (only increment if dependencies with other
+        layers are affected)
+\begin{verbatim}LAYERVERSION_mylayer = "2"\end{verbatim}
+\item set dependencies to other layers
+\begin{verbatim}LAYERDEPENDS_mylayer = "meta-yocto"\end{verbatim}
+\end{itemize}
+\end{frame}
+
+\begin{frame}
+\frametitle{Definitions}
+\begin{itemize}
+\item It is possible for a recipe with a lower version number PV in a layer
+that has a higher priority to take precedence.
+\item Also, the layer priority does not currently affect the precedence
+order of .conf or .bbclass files. Future versions of BitBake might address this.
+\end{itemize}
+\end{frame}