libbtrfsutil: add subvolume iterator helpers

This is how we can implement stuff like `btrfs subvol list`. Rather than
producing the entire list upfront, the iterator approach uses less
memory in the common case where the whole list is not stored (O(max
subvolume path length)). It supports both pre-order traversal (useful
for, e.g, recursive snapshot) and post-order traversal (useful for
recursive delete).

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/libbtrfsutil/python/tests/test_subvolume.py b/libbtrfsutil/python/tests/test_subvolume.py
index 937a4397..b43beca7 100644
--- a/libbtrfsutil/python/tests/test_subvolume.py
+++ b/libbtrfsutil/python/tests/test_subvolume.py
@@ -214,3 +214,59 @@ class TestSubvolume(BtrfsTestCase):
         wstatus = os.waitpid(pid, 0)[1]
         self.assertTrue(os.WIFEXITED(wstatus))
         self.assertEqual(os.WEXITSTATUS(wstatus), 0)
+
+    def test_subvolume_iterator(self):
+        pwd = os.getcwd()
+        try:
+            os.chdir(self.mountpoint)
+            btrfsutil.create_subvolume('foo')
+
+            path, subvol = next(btrfsutil.SubvolumeIterator('.', info=True))
+            self.assertEqual(path, 'foo')
+            self.assertIsInstance(subvol, btrfsutil.SubvolumeInfo)
+            self.assertEqual(subvol.id, 256)
+            self.assertEqual(subvol.parent_id, 5)
+
+            btrfsutil.create_subvolume('foo/bar')
+            btrfsutil.create_subvolume('foo/bar/baz')
+
+            subvols = [
+                ('foo', 256),
+                ('foo/bar', 257),
+                ('foo/bar/baz', 258),
+            ]
+
+            for arg in self.path_or_fd('.'):
+                with self.subTest(type=type(arg)):
+                    self.assertEqual(list(btrfsutil.SubvolumeIterator(arg)), subvols)
+            self.assertEqual(list(btrfsutil.SubvolumeIterator('.', top=0)), subvols)
+
+            self.assertEqual(list(btrfsutil.SubvolumeIterator('.', post_order=True)),
+                             [('foo/bar/baz', 258),
+                              ('foo/bar', 257),
+                              ('foo', 256)])
+
+            subvols = [
+                ('bar', 257),
+                ('bar/baz', 258),
+            ]
+
+            self.assertEqual(list(btrfsutil.SubvolumeIterator('.', top=256)), subvols)
+            self.assertEqual(list(btrfsutil.SubvolumeIterator('foo', top=0)), subvols)
+
+            os.rename('foo/bar/baz', 'baz')
+            self.assertEqual(sorted(btrfsutil.SubvolumeIterator('.')),
+                             [('baz', 258),
+                              ('foo', 256),
+                              ('foo/bar', 257)])
+
+            with btrfsutil.SubvolumeIterator('.') as it:
+                self.assertGreaterEqual(it.fileno(), 0)
+                it.close()
+                with self.assertRaises(ValueError):
+                    next(iter(it))
+                with self.assertRaises(ValueError):
+                    it.fileno()
+                it.close()
+        finally:
+            os.chdir(pwd)