Allow choosing snap channel on subiquity ISOs

live-build/auto/config

@@ -189,8 +189,13 @@ add_snap ()
 	_check_immutable_passes_to_layers
 	_register_pass "$pass"
 
+	local channel=""
+	if [ -n "$CHANNEL" ] ; then
+		channel="=$CHANNEL"
+	fi
+
 	for pkg; do
-		echo "$pkg" >> "config/package-lists/livecd-rootfs.snaplist.chroot_$pass.full"
+		echo "$pkg$channel" >> "config/package-lists/livecd-rootfs.snaplist.chroot_$pass.full"
 	done
 }
 
@@ -1339,6 +1344,7 @@ echo "LB_BINARY_HOOKS=\"$BINARY_HOOKS\"" >> config/binary
 echo "BUILDSTAMP=\"$NOW\"" >> config/binary
 echo "SUBPROJECT=\"${SUBPROJECT:-}\"" >> config/binary
 echo "LB_DISTRIBUTION=\"$SUITE\"" >> config/binary
+echo "CHANNEL=\"${CHANNEL:-}\"" >> config/binary
 
 if [ "${IMAGE_HAS_HARDCODED_PASSWORD:-}" = "1" ]; then
 	echo IMAGE_HAS_HARDCODED_PASSWORD=1 >> config/binary

live-build/ubuntu/hooks/020-canary-enhanced-sb.binary

@@ -107,7 +107,12 @@ Ekm0W8qT4AT0GSk5CY8kx+UvCn6FLxMuv8xjWoX3OLcQx31yO6Uy6c2LN6nSlovDghKP5V1KvlKl
 WiXM9CPKCZv/Es3uOp/ke0wWL7v0MZhzUJ+QhOtTNg==
 EOF
 
-env SNAPPY_STORE_NO_CDN=1 snap prepare-image --classic config/classic-model.model chroot
+channel=""
+if [ -n "$CHANNEL" ]; then
+    channel="--channel $CHANNEL"
+fi
+env SNAPPY_STORE_NO_CDN=1 snap prepare-image \
+    --classic config/classic-model.model $channel chroot
 mv chroot/system-seed/systems/* chroot/system-seed/systems/enhanced-secureboot-desktop
 rsync -a chroot/system-seed/ chroot/var/lib/snapd/seed
 rm -rf chroot/system-seed/

live-build/ubuntu/hooks/020-canary-live.binary

@@ -63,7 +63,12 @@ oPijs/y+KJ4DbdrmiwwWCxQZcx2T5GG4HB38eIsnmEWTyml02lOL9sWq6qKuk95a3DhF+Q02+zkG
 c3kEHr8kcSEkJtgwre/RjjlvGYhur1rZ4i0G6gGBLw==
 EOF
 
-env SNAPPY_STORE_NO_CDN=1 snap prepare-image --classic config/classic-model-installer.model chroot
+channel=""
+if [ -n "$CHANNEL" ]; then
+    channel="--channel $CHANNEL"
+fi
+env SNAPPY_STORE_NO_CDN=1 snap prepare-image \
+    --classic config/classic-model-installer.model $channel chroot
 mv chroot/system-seed/systems/* chroot/system-seed/systems/classic-installer
 rsync -a chroot/system-seed/ chroot/var/lib/snapd/seed
 rm -rf chroot/system-seed/