Allow reformatting of 'plain' btrfs volumes

Similar to previous support for btrfs subvolumes, this allows
reusing the btrfs volume directly. Only btrfs volumes without
subvolumes can be reused which allows using btrfs as a 'normal'
single device filesystem instead of using subvolumes only.

pyanaconda/modules/storage/partitioning/manual/manual_partitioning.py

@@ -85,7 +85,7 @@ def _setup_mount_point(self, storage, mount_data):
 
                 fmt = get_format(old_fmt.type)
 
-            if device.raw_device.type == "btrfs subvolume":
+            if device.raw_device.type in ("btrfs volume", "btrfs subvolume"):
                 # 'Format', or rather clear the device by recreating it
                 device = self._recreate_device(storage, device_spec)
                 mount_data.mount_options = device.format.options
@@ -105,17 +105,40 @@ def _setup_mount_point(self, storage, mount_data):
         device.format.create_options = mount_data.format_options
         device.format.options = mount_data.mount_options
 
+    def _recreate_btrfs_volume(self, storage, device):
+        """Recreate a btrfs volume device by destroying and adding it.
+
+        :param storage: an instance of the Blivet's storage object
+        :param dev_spec: a BtrfsVolumeDevice to recreate
+        """
+        if device.children:
+            raise StorageError(
+                _("Cannot reformat Btrfs volume '{}' with "
+                  "existing subvolumes").format(device.name))
+        storage.destroy_device(device)
+        for parent in device.parents:
+            storage.format_device(parent, get_format("btrfs"))
+        new_btrfs = storage.new_btrfs(parents=device.parents[:],
+                                      name=device.name)
+        storage.create_device(new_btrfs)
+        return new_btrfs
+
     def _recreate_device(self, storage, dev_spec):
         """Recreate a device by destroying and adding it.
 
         :param storage: an instance of the Blivet's storage object
         :param dev_spec: a string describing a block device to be recreated
         """
         device = storage.devicetree.resolve_device(dev_spec)
-        request = generate_device_factory_request(storage, device)
-        destroy_device(storage, device)
-        task = AddDeviceTask(storage, request)
-        task.run()
-        device = storage.devicetree.resolve_device(dev_spec)
 
-        return device
+        if device.type == "btrfs volume":
+            # can't use device factory for just the volume
+            return self._recreate_btrfs_volume(storage, device)
+        else:
+            request = generate_device_factory_request(storage, device)
+            destroy_device(storage, device)
+            task = AddDeviceTask(storage, request)
+            task.run()
+            device = storage.devicetree.resolve_device(dev_spec)
+
+            return device