feat: Add metadata on ubuntu-oci image

Add a file build.info on etc/cloud
with the serial information

Signed-off-by: Samir Akarioh <samir.akarioh@canonical.com>

live-build/auto/build

@@ -462,7 +462,12 @@ EOF
 		fi
 
 		if [ "$PROJECT" = "ubuntu-oci" ]; then
-		    configure_oci chroot
+			if [ -n "$BUILDSTAMP" ]; then
+				configure_oci chroot "$BUILDSTAMP"
+			else
+				echo "The \$BUILDSTAMP variable is empty"
+				exit 1
+			fi
 		fi
 
 		configure_network_manager

live-build/functions

@@ -922,6 +922,12 @@ configure_oci() {
     # at https://github.com/tianon/docker-brew-ubuntu-core/blob/master/update.sh
 
     local chroot=$1
+    local serial=$2
+
+    if [ ! -d "${chroot}" ]; then
+        echo "The chroot does not exist"
+        exit 1
+    fi
 
     echo "==== Configuring OCI ===="
 
@@ -930,6 +936,15 @@ configure_oci() {
     echo 'exit 101' >> ${chroot}/usr/sbin/policy-rc.d
     Chroot ${chroot} "chmod +x /usr/sbin/policy-rc.d"
 
+
+    # Inject a build stamp into the image 
+    
+    mkdir -p ${chroot}/etc/cloud
+    cat > ${chroot}/etc/cloud/build.info << EOF
+serial: $serial
+EOF
+
+
     # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L54-L56
     Chroot ${chroot} "dpkg-divert --local --rename --add /sbin/initctl"
     cp -a ${chroot}/usr/sbin/policy-rc.d ${chroot}/sbin/initctl