Add default PPC block-device layout

Add a default PPC block-device layout.  I've extracted this into
separate yaml files for ease of editing and to facilitate things like
longer comments.

This is not sufficient to get PPC images working, but it is required.

Change-Id: I09e5d1ed92260bdb632333f5203dd7e70d512dc8

diskimage_builder/elements/vm/block-device-default.yaml

@@ -0,0 +1,12 @@
+# Default single partition loopback
+
+- local_loop:
+    name: image0
+
+- partitioning:
+   base: image0
+   label: mbr
+   partitions:
+     - name: root
+       flags: [ boot, primary ]
+       size: 100%

diskimage_builder/elements/vm/block-device-ppc.yaml

@@ -0,0 +1,30 @@
+# Default block device setup for PPC
+# ----------------------------------
+#
+# Details (extracted from [1])
+#
+# Power Firmware (OFW) scans chosen (nvram value boot-device) device,
+# for either PReP* partition or vfat.
+#
+# PReP is raw and small (8M max) partition which caries only stage1
+# binary.
+#  msdos partition table:
+#   - PReP partition have 0x41 type (must be active)
+#   - PReP partition must have boot flag set
+#
+# [1] https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/W51a7ffcf4dfd_4b40_9d82_446ebc23c550/page/PowerLinux%20Boot%20howto
+
+- local_loop:
+    name: image0
+
+- partitioning:
+    base: image0
+    label: mbr
+    partitions:
+      - name: boot
+        flags: [ boot, primary ]
+        type: '0x41'
+        size: 8MiB
+      - name: root
+        flags: [ primary ]
+        size: 100%

diskimage_builder/elements/vm/environment.d/10-partitioning

@@ -1,15 +1,14 @@
-export DIB_BLOCK_DEVICE_DEFAULT_CONFIG="
-- local_loop:
-    name: image0
+_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
-- partitioning:
-   base: image0
-   label: mbr
-   partitions:
-     - name: root
-       flags: [ boot, primary ]
-       size: 100%
-"
+if [[ "$ARCH" =~ "ppc" ]] ; then
+    DIB_BLOCK_DEVICE_DEFAULT_CONFIG="$(cat $_DIR/../block-device-ppc.yaml)"
+else
+    DIB_BLOCK_DEVICE_DEFAULT_CONFIG="$(cat $_DIR/../block-device-default.yaml)"
+fi
 
 DIB_BLOCK_DEVICE_CONFIG=${DIB_BLOCK_DEVICE_CONFIG:-${DIB_BLOCK_DEVICE_DEFAULT_CONFIG}}
 export DIB_BLOCK_DEVICE_CONFIG
+
+# Local variables:
+# mode: sh
+# End: