install_pkgs uses named volumes to work with DIND.

docker/package_managers/installer.sh.tpl

@@ -1,11 +1,10 @@
 #!/bin/bash
 # This script installs debs in installables.tar through dpkg and apt-get.
-# It expects to be volume-mounted inside a docker image, in /tmp along with the
-# installables.tar.
+# It expects to be volume-mounted inside a docker image, in /tmp/pkginstall
+# along with the installables.tar.
 set -ex
-pushd /tmp
+pushd /tmp/pkginstall
 %{install_commands}
 popd
-umount -l /tmp/installer.sh
-umount -l /tmp/%{installables_tar}
+umount -l /tmp/pkginstall
 rm -rf /tmp/*

docker/package_managers/run_install.sh.tpl

@@ -17,11 +17,41 @@ source %{util_script}
 image_id=$(%{image_id_extractor_path} %{base_image_tar})
 $DOCKER load -i %{base_image_tar}
 
+# Create a docker volume containing the installer script and the
+# installables TAR file.
+#
+# Note that we cannot mount local files and directories
+# directly into the container, since it doesn't work correctly
+# in docker-in-docker setups.  In docker-in-docker setups, we
+# are running in a container while the docker daemon is running
+# on a host.  Mounting directories is done from the perspective
+# of the host and not our container.
+#
+# To get around this, we create a named volume and copy our files
+# to the named volume.
+
+# Prepare directory structure. 'docker cp' will not create
+# intermediate paths.
+tmpdir=$(mktemp -d)
+trap "rm -rf $tmpdir" EXIT
+mkdir -p $(dirname $tmpdir/%{installables_tar})
+cp -L $(pwd)/%{installables_tar} $tmpdir/%{installables_tar}
+cp -L $(pwd)/%{installer_script} $tmpdir/installer.sh
+# Temporarily create a container so we can mount the named volume
+# and copy files.  It's okay if /bin/true doesn't exist inside the
+# image; we are never going to run the image anyways.
+vid=$($DOCKER volume create)
+cid=$($DOCKER create -v $vid:/tmp/pkginstall $image_id /bin/true)
+for f in $tmpdir/*; do
+    $DOCKER cp $f $cid:/tmp/pkginstall
+done
+$DOCKER rm $cid
 
-cid=$($DOCKER run -d -v $(pwd)/%{installables_tar}:/tmp/%{installables_tar} -v $(pwd)/%{installer_script}:/tmp/installer.sh --privileged $image_id /tmp/installer.sh)
+cid=$($DOCKER run -d -v $vid:/tmp/pkginstall --privileged $image_id /tmp/pkginstall/installer.sh)
 
 $DOCKER attach $cid || true
 
 reset_cmd $image_id $cid %{output_image_name}
 $DOCKER save %{output_image_name} > %{output_file_name}
 $DOCKER rm $cid
+$DOCKER volume rm $vid