kas-docker: Make loop device passing optional

This used to be required in older Isar versions (prio to commit
8b8a339cfaa4) for one configuration. It may still be required by
downstream layers, though it can be avoided. To overcome this
potential need to enter the host's root password without breaking those
cases, keep the feature but make it explicit (--with-loop-dev option).

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas-docker

@@ -37,6 +37,9 @@ usage()
 	printf "%b" "clean\t\t\tClean build artifacts, keep downloads.\n"
 	printf "%b" "\nOptional arguments:\n"
 	printf "%b" "--isar\t\t\tUse kas-isar container to build Isar image.\n"
+	printf "%b" "--with-loop-dev		Pass a loop device to the " \
+		    "container. Only required if\n"
+	printf "%b" "\t\t\tloop-mounting is used by recipes.\n"
 	printf "%b" "--docker-args\t\tAdditional arguments to pass to docker " \
 		    "for running the\n"
 	printf "%b" "\t\t\tbuild.\n"
@@ -73,6 +76,10 @@ while [ $# -gt 0 ]; do
 	case "$1" in
 	--isar)
 		DOCKER_IMAGE=kasproject/kas-isar:${KAS_IMAGE_VERSION}
+		ISAR_ARGS="--cap-add=SYS_ADMIN --cap-add=MKNOD --privileged"
+		shift 1
+		;;
+	--with-loop-dev)
 		if ! LOOP_DEV=$(/sbin/losetup -f 2>/dev/null); then
 			if [ $(id -u) -eq 0 ]; then
 				echo "Error: loop device not available!"
@@ -90,8 +97,7 @@ while [ $# -gt 0 ]; do
 				exit 1
 			fi
 		fi
-		ISAR_ARGS="--cap-add=SYS_ADMIN --cap-add=MKNOD --privileged \
-			--device ${LOOP_DEV}"
+		WITH_LOOP_DEV="--device ${LOOP_DEV}"
 		shift 1
 		;;
 	--docker-args)
@@ -267,5 +273,5 @@ if [ -z "${NO_PROXY_FROM_ENV+x}" ]; then
 	done
 fi
 
-trace docker run "$@" ${ISAR_ARGS} ${USER_ARGS} \
+trace docker run "$@" ${ISAR_ARGS} ${WITH_LOOP_DEV} ${USER_ARGS} \
 		 ${DOCKER_IMAGE} ${CMD} ${KAS_OPTIONS} ${KAS_FILES}