Adding losetup utility package to core pkg

Signed-off-by: Christian Wuerdig <christian.wuerdig@gmail.com>

pkg/losetup/Dockerfile

@@ -0,0 +1,18 @@
+FROM linuxkit/alpine:3683c9a66cd4da40bd7d6c7da599b2dcd738b559 AS mirror
+RUN mkdir -p /out/etc/apk && cp -r /etc/apk/* /out/etc/apk/
+RUN apk add --no-cache --initdb -p /out  \
+    alpine-baselayout \
+    busybox
+
+# Remove apk residuals
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
+
+FROM scratch
+ENTRYPOINT []
+WORKDIR /
+COPY --from=mirror /out/ /
+
+COPY loopy.sh /usr/bin/loopy
+RUN chmod +x /usr/bin/loopy
+
+CMD ["/usr/bin/loopy"]

pkg/losetup/build.yml

@@ -0,0 +1,7 @@
+image: losetup
+config:
+  binds:
+    - /dev:/dev
+    - /var:/var
+  capabilities:
+    - CAP_SYS_ADMIN

pkg/losetup/loopy.sh

@@ -0,0 +1,57 @@
+#!/bin/sh
+
+set -e
+
+help()
+{
+    echo "Usage: $0 [options] <file>"
+    echo
+    echo "Options:"
+    echo "    -c, --create          Create <file> if not present, default: false"
+    echo "    -s, --size NUM        Size of <file> in MiB if it gets created, default: 10"
+    echo "    -d, --dev DEVICE      Use DEVICE as loop device, default: /dev/loop0"
+    echo
+}
+
+create=false
+size_mib=10
+loop_device="/dev/loop0"
+
+O=`getopt -l create,size:,dev:,help -- cs:d:h "$@"` || exit 1
+eval set -- "$O"
+while true; do
+    case "$1" in
+        -c|--create)   create=true; shift;;
+        -s|--size)     size_mib=$2; shift 2;;
+        -d|--dev)      loop_device=$2; shift 2;;
+        -h|--help)     help; exit 0;;
+        --)            shift; break;;
+        *)             echo "Unknown option $1"; help; exit 1;;
+	esac
+done
+
+if [ -z "$1" ]; then
+    echo "Missing argument <file>"
+    help
+    exit 1
+fi
+
+container_file=$1
+
+if [ ! -b "$loop_device" ]; then
+    echo "Loop device $loop_device doesn't exist! Did you forget to bind-mount '/dev'?"
+    exit 2
+fi
+
+if [ ! -f "$container_file" ]; then
+    if [ $create = true ]; then
+        echo "File $container_file not found, creating new one of size $size_mib MiB"
+        dd if="/dev/zero" of="$container_file" bs=1M count=$size_mib
+    else
+        echo "File $container_file not found. Please specify --create or ensure it's present."
+        exit 2
+    fi
+fi
+
+echo "Associating file $container_file with loop device $loop_device"
+losetup "$loop_device" "$container_file"