rootfs-postcommands: add QA check for overlayfs

The check is conditional and only enabled when overlayfs is set in
DISTRO_FEATURES

(From OE-Core rev: 4734799bacf0a5d2487e1cde3ae1c00223b032b2)

Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/rootfs-postcommands.bbclass

@@ -39,6 +39,8 @@ ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains("DISTRO_FEATURES", "systemd"
 
 ROOTFS_POSTPROCESS_COMMAND += 'empty_var_volatile;'
 
+ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains("DISTRO_FEATURES", "overlayfs", "overlayfs_qa_check;", "", d)}'
+
 inherit image-artifact-names
 
 # Sort the user and group entries in /etc by ID in order to make the content
@@ -373,3 +375,26 @@ rootfs_reproducible () {
 		fi
 	fi
 }
+
+python overlayfs_qa_check() {
+    from oe.overlayfs import mountUnitName
+
+    # this is a dumb check for unit existence, not its validity
+    overlayMountPoints = d.getVarFlags("OVERLAYFS_MOUNT_POINT")
+    imagepath = d.getVar("IMAGE_ROOTFS")
+    searchpaths = [oe.path.join(imagepath, d.getVar("sysconfdir"), "systemd", "system"),
+                   oe.path.join(imagepath, d.getVar("systemd_system_unitdir"))]
+
+    allUnitExist = True;
+    for mountPoint in overlayMountPoints:
+        path = d.getVarFlag('OVERLAYFS_MOUNT_POINT', mountPoint)
+        unit = mountUnitName(path)
+
+        if not any(os.path.isfile(oe.path.join(dirpath, unit))
+                   for dirpath in searchpaths):
+            bb.warn('Unit name %s not found in systemd unit directories' % unit)
+            allUnitExist = False;
+
+    if not allUnitExist:
+        bb.fatal('Not all mount units are installed by the BSP')
+}