Add support for mounting external containers

Continue progress on use of external containers.

This PR adds the ability to mount, umount and list the
storage containers whether they are in libpod or not.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

libpod/runtime_ctr.go

@@ -918,6 +918,56 @@ func (r *Runtime) PruneContainers(filterFuncs []ContainerFilter) (map[string]int
 	return prunedContainers, pruneErrors, nil
 }
 
+// MountStorageContainer mounts the storage container's root filesystem
+func (r *Runtime) MountStorageContainer(id string) (string, error) {
+	if _, err := r.GetContainer(id); err == nil {
+		return "", errors.Wrapf(define.ErrCtrExists, "ctr %s is a libpod container", id)
+	}
+	container, err := r.store.Container(id)
+	if err != nil {
+		return "", err
+	}
+	mountPoint, err := r.store.Mount(container.ID, "")
+	if err != nil {
+		return "", errors.Wrapf(err, "error mounting storage for container %s", id)
+	}
+	return mountPoint, nil
+}
+
+// UnmountStorageContainer unmounts the storage container's root filesystem
+func (r *Runtime) UnmountStorageContainer(id string, force bool) (bool, error) {
+	if _, err := r.GetContainer(id); err == nil {
+		return false, errors.Wrapf(define.ErrCtrExists, "ctr %s is a libpod container", id)
+	}
+	container, err := r.store.Container(id)
+	if err != nil {
+		return false, err
+	}
+	return r.store.Unmount(container.ID, force)
+}
+
+// MountedStorageContainer returns whether a storage container is mounted
+// along with the mount path
+func (r *Runtime) IsStorageContainerMounted(id string) (bool, string, error) {
+	var path string
+	if _, err := r.GetContainer(id); err == nil {
+		return false, "", errors.Wrapf(define.ErrCtrExists, "ctr %s is a libpod container", id)
+	}
+
+	mountCnt, err := r.storageService.MountedContainerImage(id)
+	if err != nil {
+		return false, "", err
+	}
+	mounted := mountCnt > 0
+	if mounted {
+		path, err = r.storageService.GetMountpoint(id)
+		if err != nil {
+			return false, "", err
+		}
+	}
+	return mounted, path, nil
+}
+
 // StorageContainers returns a list of containers from containers/storage that
 // are not currently known to Podman.
 func (r *Runtime) StorageContainers() ([]storage.Container, error) {