feat: Support for creating volumes without a FS

Currently whenever volume is created without fs_type specification, a filesystem of default
type (i.e. xfs) is automatically put on it.
This change allows user to prevent FS creation by explicitly using "unformatted" value as a fs_type option.
In the same manner it also allows to remove an existing FS. To be able to do that the safe mode has to be off.

README.md

@@ -143,6 +143,9 @@ variables:
   This indicates the desired file system type to use, e.g.: "xfs", "ext4", "swap".
   The default is determined according to the OS and release
   (currently `xfs` for all the supported systems).
+  Use "unformatted" if you do not want file system to be present.
+  __WARNING__: Using "unformatted" file system type on an existing filesystem
+               is a destructive operation and will destroy all data on the volume.
 
 - `fs_label`
 

library/blivet.py

@@ -20,7 +20,7 @@
 description:
     - "WARNING: Do not use this module directly! It is only for role internal use."
     - "Module configures storage pools and volumes to match the state specified
-       in input parameters. It does not do any management of /etc/fstab entries."
+       in input parameters."
 
 options:
     pools:
@@ -435,6 +435,11 @@ def _apply_defaults(self):
 
     def _get_format(self):
         """ Return a blivet.formats.DeviceFormat instance for this volume. """
+
+        if self._volume['fs_type'].lower() == 'unformatted':
+            # Do not create any fs when user explicitly said so
+            return None
+
         fmt = get_format(self._volume['fs_type'],
                          mountpoint=self._volume.get('mount_point'),
                          label=self._volume['fs_label'],
@@ -560,7 +565,8 @@ def _reformat(self):
         """ Schedule actions as needed to ensure the volume is formatted as specified. """
         fmt = self._get_format()
 
-        if self._device.format.type == fmt.type:
+        if ((fmt is None and self._device.format.type is None)
+                or (fmt is not None and self._device.format.type == fmt.type)):
             # format is the same, no need to run reformatting
             dev_label = '' if self._device.format.label is None else self._device.format.label
             if dev_label != fmt.label:
@@ -574,9 +580,10 @@ def _reformat(self):
 
         if self._device.format.status and (self._device.format.mountable or self._device.format.type == "swap"):
             self._device.format.teardown()
-        if not self._device.isleaf:
+        if not self._device.isleaf or fmt is None:
             self._blivet.devicetree.recursive_remove(self._device, remove_device=False)
-        self._blivet.format_device(self._device, fmt)
+        if fmt is not None:
+            self._blivet.format_device(self._device, fmt)
 
     def manage(self):
         """ Schedule actions to configure this volume according to the yaml input. """

tests/test-verify-volume-fs.yml

@@ -3,7 +3,9 @@
 - name: Verify fs type
   assert:
     that: storage_test_blkinfo.info[storage_test_volume._device].fstype ==
-      storage_test_volume.fs_type
+      storage_test_volume.fs_type or
+      (storage_test_blkinfo.info[storage_test_volume._device].fstype | length
+       == 0 and storage_test_volume.fs_type == "unformatted")
   when: storage_test_volume.fs_type and _storage_test_volume_present
 
 # label

tests/tests_change_fs.yml

@@ -101,6 +101,22 @@
     - name: Verify role results
       include_tasks: verify-role-results.yml
 
+    - name: Remove the FS
+      include_role:
+        name: linux-system-roles.storage
+      vars:
+        storage_pools:
+          - name: foo
+            disks: "{{ unused_disks }}"
+            volumes:
+              - name: test1
+                size: "{{ volume_size }}"
+                fs_type: unformatted
+
+    - name: Verify role results
+      include_tasks: verify-role-results.yml
+
+
     - name: Clean up
       include_role:
         name: linux-system-roles.storage