wic: Extend indirect string connection to support image names and rootfs

The wic command-line param --rootfs-dir gets extended to support
multiple directories and image names. Each '--rootfs-dir' could be
connected using a special string. This special string is a image
name which gets expanded by bitbake to get 'IMAGE_ROOTFS' or
a rootfs-dir path pointing to rootfs directory. Like this:

  wic create ... --rootfs-dir rootfs1=core-image-minimal \
    --rootfs-dir rootfs2=core-image-minimal-dev

.wks:

  part / --source rootfs --rootfs-dir="rootfs1" --ondisk sda --fstype=ext3 \
    --label primary --align 1024

  part /standby --source rootfs --rootfs-dir="rootfs2" \
    --ondisk sda --fstype=ext3 --label secondary --align 1024

(From OE-Core rev: 58417093d7ce83c8a2f683a356fddc23aaee5e8e)

Signed-off-by: João Henrique Ferreira de Freitas <joaohf@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/mic/plugins/source/rootfs.py

@@ -43,6 +43,25 @@ from mic.imager.direct import DirectImageCreator
 class RootfsPlugin(SourcePlugin):
     name = 'rootfs'
 
+    @staticmethod
+    def __get_rootfs_dir(rootfs_dir):
+        if os.path.isdir(rootfs_dir):
+            return rootfs_dir
+
+        bitbake_env_lines = find_bitbake_env_lines(rootfs_dir)
+        if not bitbake_env_lines:
+            msg = "Couldn't get bitbake environment, exiting."
+            msger.error(msg)
+
+        image_rootfs_dir = find_artifact(bitbake_env_lines, "IMAGE_ROOTFS")
+        if not os.path.isdir(image_rootfs_dir):
+            msg = "No valid artifact IMAGE_ROOTFS from image named"
+            msg += " %s has been found at %s, exiting.\n" % \
+                (rootfs_dir, image_rootfs_dir)
+            msger.error(msg)
+
+        return image_rootfs_dir
+
     @classmethod
     def do_prepare_partition(self, part, cr, cr_workdir, oe_builddir, bootimg_dir,
                              kernel_dir, krootfs_dir, native_sysroot):
@@ -59,13 +78,15 @@ class RootfsPlugin(SourcePlugin):
         else:
             if part.rootfs in krootfs_dir:
                 rootfs_dir = krootfs_dir[part.rootfs]
-            elif os.path.isdir(part.rootfs):
+            elif part.rootfs:
                 rootfs_dir = part.rootfs
             else:
                 msg = "Couldn't find --rootfs-dir=%s connection"
                 msg += " or it is not a valid path, exiting"
                 msger.error(msg % part.rootfs)
 
-        part.set_rootfs(rootfs_dir)
+        real_rootfs_dir = self.__get_rootfs_dir(rootfs_dir)
-        part.prepare_rootfs(cr_workdir, oe_builddir, rootfs_dir, native_sysroot)
+
+        part.set_rootfs(real_rootfs_dir)
+        part.prepare_rootfs(cr_workdir, oe_builddir, real_rootfs_dir, native_sysroot)