Do not include any snaps in ubuntu-cpc:minimized builds

debian/changelog

@@ -1,3 +1,18 @@
+livecd-rootfs (2.577) UNRELEASED; urgency=medium
+
+  [ Tobias Koch ]
+  * Detect which core snaps are required and install them on-the-fly.
+
+  [ Michael Hudson-Doyle ]
+  * Slim down ubuntu-cpc:minimized builds:
+    - Do not include any snaps in ubuntu-cpc:minimized builds (erroring if any
+      snap other than lxd is seeded).
+    - Install the lxd-installer package instead, which installs the lxd snap
+      when invoked.
+    - Install lxd snap in unminimize.
+
+ -- Tobias Koch <tobias.koch@canonical.com>  Thu, 11 Apr 2019 17:25:25 +0200
+
 livecd-rootfs (2.576) disco; urgency=medium
 
   * When the "snap-tool" script encounters a core snap it will switch to

live-build/auto/build

@@ -226,7 +226,17 @@ if dpkg-query --show --showformat='${db:Status-Status}\n' ubuntu-server 2> /dev/
 fi
 EOF
 fi
-                cat >> chroot/usr/local/sbin/unminimize <<'EOF'
+		if [ "$PROJECT" = "ubuntu-cpc" ]; then
+			cat >> chroot/usr/local/sbin/unminimize <<'EOF'
+
+echo "Removing lxd installer package..."
+apt-get purge -y lxd-installer
+
+echo "Installing lxd from snap..."
+snap install lxd
+EOF
+		fi
+		cat >> chroot/usr/local/sbin/unminimize <<'EOF'
 
 # unminimization succeeded, there is no need to mention it in motd
 rm -f /etc/update-motd.d/60-unminimize

live-build/auto/config

@@ -807,7 +807,7 @@ case $PROJECT in
 	ubuntu-cpc)
 		if [ "${SUBPROJECT:-}" = minimized ]; then
 			add_task install cloud-image
-			add_package install sudo
+			add_package install sudo lxd-installer
 			# linux-kvm currently only exists for amd64, so fall back to the
 			# virtual flavour for other architectures
 			if [ "$ARCH" = "amd64" ]; then
@@ -896,6 +896,25 @@ esac
 if [ "$PASSES_TO_LAYERS" != "true" ] && [ -n "${BASE_SEED}" ]; then
 	snap_from_seed "${BASE_SEED}" config/seeded-snaps
 fi
+if [ "$PROJECT:${SUBPROJECT:-}" = ubuntu-cpc:minimized ]; then
+	# We install a lxc script that installs the snap when invoked. We don't
+	# want any other snaps to come in without due consideration, so fail the
+	# build if we see such a snap.
+	for snap in `cat config/seeded-snaps`; do
+		case $snap in
+			lxd)
+				;;
+			*)
+				echo "Unexpected seeded snap for ubuntu-cpc:minimized build: $snap"
+				exit 1
+				;;
+		esac
+	done
+
+	# Truncate but don't delete to a) prevent any snaps from being seeded,
+	# while at the same time b) triggering initialization of assertions.
+	truncate --size 0 config/seeded-snaps
+fi
 
 # grab a list of packags to remove for a "minimal" installation from the seed
 # mirror for this project

live-build/functions

@@ -436,6 +436,17 @@ _snap_preseed() {
         return
     fi
 
+    # Determine if and what core snap is needed
+    local core_snap=$(/usr/share/livecd-rootfs/snap-tool info \
+        --cohort-key="${COHORT_KEY:-}" \
+        --channel="$CHANNEL" "$SNAP_NAME" | \
+        grep '^base:' | awk '{print $2}'
+    )
+
+    if [ -n "$core_snap" ]; then
+        _snap_preseed $CHROOT_ROOT $core_snap stable
+    fi
+
     sh -c "
         set -x;
         cd \"$CHROOT_ROOT/var/lib/snapd/seed\";
@@ -544,9 +555,6 @@ snap_prepare() {
     local CUSTOM_BRAND_MODEL=${2:-generic:generic-classic}
 
     snap_prepare_assertions "$CHROOT_ROOT" "$CUSTOM_BRAND_MODEL"
-
-    # Download the core snap
-    _snap_preseed $CHROOT_ROOT core stable
 }
 
 snap_preseed() {