Add a new function to check if a filesystem is empty

This will be used by Anaconda to determine whether a given
filesystem can be used for / without reformating.

blivet/devicelibs/btrfs.py

@@ -20,7 +20,15 @@
 # Author(s): David Lehman <dlehman@redhat.com>
 #
 
+import os
+
+import gi
+gi.require_version("BlockDev", "3.0")
+
+from gi.repository import BlockDev
+
 from . import raid
+from ..errors import BTRFSError
 from ..size import Size
 from ..tasks import availability
 
@@ -45,3 +53,16 @@
 
 def is_btrfs_name_valid(name):
     return '\x00' not in name
+
+
+def get_mountpoint_subvolumes(mountpoint):
+    """ Get list of subvolume names on given mounted btrfs filesystem
+    """
+    if not os.path.ismount(mountpoint):
+        raise ValueError("%s doesn't seem to be a mountpoint" % mountpoint)
+    try:
+        subvols = BlockDev.btrfs.list_subvolumes(mountpoint)
+    except BlockDev.BtrfsError as e:
+        raise BTRFSError(str(e))
+    else:
+        return [s.path for s in subvols]

blivet/formats/fs.py

@@ -28,6 +28,7 @@
 import uuid as uuid_mod
 import random
 import stat
+from contextlib import contextmanager
 
 from parted import fileSystemType, PARTITION_BOOT
 
@@ -61,6 +62,7 @@
 from ..i18n import N_
 from .. import udev
 from ..mounts import mounts_cache
+from ..devicelibs import btrfs
 
 from .fslib import kernel_filesystems, FSResize
 
@@ -97,6 +99,9 @@ class FS(DeviceFormat):
     # support for resize: grow/shrink, online/offline
     _resize_support = 0
 
+    # directories that even a newly created empty filesystem can contain (e.g. lost+found)
+    _system_dirs = []
+
     config_actions_map = {"label": "write_label",
                           "mountpoint": "change_mountpoint"}
 
@@ -557,6 +562,49 @@ def test_mount(self):
 
         return ret
 
+    @contextmanager
+    def _do_temp_mount(self):
+        if not self.exists:
+            raise FSError("format doesn't exist")
+
+        if not self.mountable:
+            raise FSError("format cannot be mounted")
+
+        if not self.device:
+            raise FSError("no device associated with the format")
+
+        if self.status:
+            yield self.system_mountpoint
+
+        else:
+            tmpdir = tempfile.mkdtemp(prefix="blivet-tmp.%s" % os.path.basename(self.device))
+            try:
+                util.mount(device=self.device, mountpoint=tmpdir, fstype=self.type,
+                           options=self.mountopts)
+            except FSError as e:
+                log.debug("temp mount failed: %s", e)
+                raise
+
+            try:
+                yield tmpdir
+            finally:
+                util.umount(mountpoint=tmpdir)
+                os.rmdir(tmpdir)
+
+    @property
+    def is_empty(self):
+        """ Check whether this filesystem os empty or not
+
+            Note: If the filesystem is not mounted, this will temporarily mount it
+                  to a temporary directory.
+        """
+
+        with self._do_temp_mount() as mnt:
+            content = os.listdir(mnt)
+            if content and not all(c in self._system_dirs for c in content):
+                return False
+            return True
+
     def _pre_setup(self, **kwargs):
         """ Check to see if the filesystem should be mounted.
 
@@ -893,6 +941,7 @@ class Ext2FS(FS):
     _writeuuid_class = fswriteuuid.Ext2FSWriteUUID
     parted_system = fileSystemType["ext2"]
     _metadata_size_factor = 0.93  # ext2 metadata may take 7% of space
+    _system_dirs = ["lost+found"]
 
     def _post_setup(self, **kwargs):
         super(Ext2FS, self)._post_setup(**kwargs)
@@ -1037,6 +1086,21 @@ def container_uuid(self):
     def container_uuid(self, uuid):
         self.vol_uuid = uuid
 
+    @property
+    def is_empty(self):
+        """ Check whether this filesystem os empty or not
+
+            Note: If the filesystem is not mounted, this will temporarily mount it
+                  to a temporary directory.
+        """
+
+        with self._do_temp_mount() as mnt:
+            content = os.listdir(mnt)
+            subvols = btrfs.get_mountpoint_subvolumes(mnt)
+            if content and not all(c in self._system_dirs + subvols for c in content):
+                return False
+            return True
+
 
 register_device_format(BTRFS)
 

tests/storage_tests/devices_test/btrfs_test.py

@@ -1,4 +1,5 @@
 import os
+import tempfile
 import unittest
 
 from ..storagetestcase import StorageTestCase
@@ -152,3 +153,63 @@ def test_btrfs_raid_raid0(self):
 
     def test_btrfs_raid_raid1(self):
         self._test_btrfs_raid(blivet.devicelibs.raid.RAID1)
+
+    def test_btrfs_fs_is_empty(self):
+        disk = self.storage.devicetree.get_device_by_path(self.vdevs[0])
+        self.assertIsNotNone(disk)
+
+        self.storage.initialize_disk(disk)
+
+        part = self.storage.new_partition(size=blivet.size.Size("1 GiB"), fmt_type="btrfs",
+                                          parents=[disk])
+        self.storage.create_device(part)
+
+        blivet.partitioning.do_partitioning(self.storage)
+
+        vol = self.storage.new_btrfs(name=self.volname, parents=[part])
+        self.storage.create_device(vol)
+
+        self.assertIsNotNone(vol.uuid)
+
+        sub1 = self.storage.new_btrfs_sub_volume(parents=[vol], name="blivetTestSubVol1")
+        self.storage.create_device(sub1)
+
+        sub2 = self.storage.new_btrfs_sub_volume(parents=[vol], name="blivetTestSubVol2")
+        self.storage.create_device(sub2)
+
+        sub3 = self.storage.new_btrfs_sub_volume(parents=[sub2], name="blivetTestSubVol2/blivetTestSubVol3")
+        self.storage.create_device(sub3)
+
+        self.storage.do_it()
+        self.storage.reset()
+        self.storage.reset()
+
+        vol = self.storage.devicetree.get_device_by_name(self.volname)
+        self.assertIsNotNone(vol)
+
+        self.assertTrue(vol.format.is_empty)
+        for sub in vol.subvolumes:
+            self.assertTrue(sub.format.is_empty)
+
+        # create a new directory in the second subvolume
+        with tempfile.TemporaryDirectory() as mountpoint:
+            vol.format.mount(mountpoint=mountpoint)
+            os.makedirs(os.path.join(mountpoint, "blivetTestSubVol2/test"))
+            vol.format.unmount()
+
+        self.assertTrue(vol.format.is_empty)
+
+        # first subvolume is empty
+        sub1 = self.storage.devicetree.get_device_by_name("blivetTestSubVol1")
+        self.assertIsNotNone(sub1)
+        self.assertTrue(sub1.format.is_empty)
+
+        # second subvolume is NOT empty
+        sub2 = self.storage.devicetree.get_device_by_name("blivetTestSubVol2")
+        self.assertIsNotNone(sub2)
+        self.assertFalse(sub2.format.is_empty)
+
+        # third subvolume is also empty
+        sub3 = self.storage.devicetree.get_device_by_name("blivetTestSubVol2/blivetTestSubVol3")
+        self.assertIsNotNone(sub3)
+        self.assertTrue(sub3.format.is_empty)

tests/storage_tests/formats_test/fs_test.py

@@ -87,6 +87,23 @@ def test_create_options(self):
         out = capture_output(["blkid", "-sUUID", "-ovalue", self.loop_devices[0]])
         self.assertEqual(out.strip(), uuid)
 
+    def test_fs_is_empty(self):
+        an_fs = self._fs_class()
+        if not an_fs.formattable:
+            self.skipTest("can not create filesystem %s" % an_fs.name)
+        an_fs.device = self.loop_devices[0]
+        self.assertIsNone(an_fs.create())
+
+        self.assertTrue(an_fs.is_empty)
+
+        with tempfile.TemporaryDirectory() as mountpoint:
+            an_fs.mount(mountpoint=mountpoint)
+            os.makedirs(os.path.join(mountpoint, "test"))
+            an_fs.unmount()
+            self.assertFalse(an_fs.is_empty)
+
+        self.assertFalse(an_fs.is_empty)
+
 
 class FATFSTestCase(fstesting.FSAsRoot):
     _fs_class = fs.FATFS
@@ -195,6 +212,23 @@ def test_too_big2(self):
         # XXX this tests assumes that resizing to max size - 1 B will fail, but xfs_grow won't
         self.skipTest("Not checking resize for this test category.")
 
+    def test_fs_is_empty(self):
+        an_fs = self._fs_class()
+        if not an_fs.formattable:
+            self.skipTest("can not create filesystem %s" % an_fs.name)
+        an_fs.device = self.loop_devices[0]
+        self.assertIsNone(an_fs.create())
+
+        self.assertTrue(an_fs.is_empty)
+
+        with tempfile.TemporaryDirectory() as mountpoint:
+            an_fs.mount(mountpoint=mountpoint)
+            os.makedirs(os.path.join(mountpoint, "test"))
+            an_fs.unmount()
+            self.assertFalse(an_fs.is_empty)
+
+        self.assertFalse(an_fs.is_empty)
+
 
 class HFSPlusTestCase(fstesting.FSAsRoot):
     _fs_class = fs.HFSPlus