iso: Clean up cache for guestmount

When partial cleanup messes up the guestfs cache, the call to guestmount
will fail. To fix that, let's check if there is a problem first and
clean up everything if needed.

Relates: https://bugzilla.redhat.com/show_bug.cgi?id=1771976
JIRA: COMPOSE-3932
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/wrappers/iso.py

@@ -417,6 +417,28 @@ def mount(image, logger=None, use_guestmount=True):
             # LIBGUESTFS_BACKEND=direct: running qemu directly without libvirt
             env = {'LIBGUESTFS_BACKEND': 'direct', 'LIBGUESTFS_DEBUG': '1', 'LIBGUESTFS_TRACE': '1'}
             cmd = ["guestmount", "-a", image, "-m", "/dev/sda", mount_dir]
+            # guestmount caches files for faster mounting. However,
+            # systemd-tmpfiles is cleaning it up if the files have not been
+            # used in 30 days. It seems to be leaving an empty appliance.d
+            # directory in place, which is causing guestmount to fail because
+            # the files are missing and it only checks the directory.
+            #
+            # Thus we check if the directory is empty, and remove it in such
+            # case. There is still a possible race condition that the cleanup
+            # will happen between our check and libguestfs using the directory.
+            # The performance penalty for never reusing the cached files is too
+            # high given how unlikely the race condition is.
+            #
+            # https://bugzilla.redhat.com/show_bug.cgi?id=1771976
+            guestfs_tmp_dir = "/var/tmp/.guestfs-%d" % os.getuid()
+            try:
+                if not os.listdir(os.path.join(guestfs_tmp_dir, "appliance.d")):
+                    if logger:
+                        logger.info("Cleaning up %s", guestfs_tmp_dir)
+                    util.rmtree(guestfs_tmp_dir)
+            except OSError:
+                # The directory is missing. That's fine for us too.
+                pass
         else:
             env = {}
             cmd = ["mount", "-o", "loop", image, mount_dir]

tests/test_iso_wrapper.py

@@ -3,7 +3,7 @@
 import itertools
 import mock
 import os
-import sys
+import six
 try:
     import unittest2 as unittest
 except ImportError:
@@ -19,6 +19,24 @@ Supported ISO: no
 
 INCORRECT_OUTPUT = '''This should never happen: File not found'''
 
+# Cached to use in tests that mock os.listdir
+orig_listdir = os.listdir
+
+
+def fake_listdir(pattern, result=None, exc=None):
+    """Create a function that mocks os.listdir. If the path contains pattern,
+    result will be returned or exc raised. Otherwise it's normal os.listdir
+    """
+    # The point of this is to avoid issues on Python 2, where apparently
+    # isdir() is using listdir(), so the mocking is breaking it.
+    def worker(path):
+        if isinstance(path, six.string_types) and pattern in path:
+            if exc:
+                raise exc
+            return result
+        return orig_listdir(path)
+    return worker
+
 
 class TestIsoUtils(unittest.TestCase):
 
@@ -60,9 +78,49 @@ class TestIsoUtils(unittest.TestCase):
         self.assertTrue(unmount_call_str.startswith("call(['umount'"))
         self.assertFalse(os.path.isdir(temp_dir))
 
+    @mock.patch("pungi.util.rmtree")
+    @mock.patch("os.listdir", new=fake_listdir("guestfs", ["root"]))
     @mock.patch('pungi.util.run_unmount_cmd')
     @mock.patch('pungi.wrappers.iso.run')
-    def test_guestmount(self, mock_run, mock_unmount):
+    def test_guestmount(self, mock_run, mock_unmount, mock_rmtree):
+        # first tuple is return value for command 'which guestmount'
+        # value determines type of the mount/unmount command ('0' - guestmount is available)
+        # for approach as a non-root, pair commands guestmount-fusermount are used
+        mock_run.side_effect = [(0, ''), (0, '')]
+        with iso.mount('dummy') as temp_dir:
+            self.assertTrue(os.path.isdir(temp_dir))
+        self.assertEqual(len(mock_run.call_args_list), 2)
+        mount_call_str = str(mock_run.call_args_list[1])
+        self.assertTrue(mount_call_str.startswith("call(['guestmount'"))
+        self.assertEqual(len(mock_unmount.call_args_list), 1)
+        unmount_call_str = str(mock_unmount.call_args_list[0])
+        self.assertTrue(unmount_call_str.startswith("call(['fusermount'"))
+        self.assertFalse(os.path.isdir(temp_dir))
+
+    @mock.patch("pungi.util.rmtree")
+    @mock.patch("os.listdir", new=fake_listdir("guestfs", []))
+    @mock.patch('pungi.util.run_unmount_cmd')
+    @mock.patch('pungi.wrappers.iso.run')
+    def test_guestmount_cleans_up_cache(self, mock_run, mock_unmount, mock_rmtree):
+        # first tuple is return value for command 'which guestmount'
+        # value determines type of the mount/unmount command ('0' - guestmount is available)
+        # for approach as a non-root, pair commands guestmount-fusermount are used
+        mock_run.side_effect = [(0, ''), (0, '')]
+        with iso.mount('dummy') as temp_dir:
+            self.assertTrue(os.path.isdir(temp_dir))
+        self.assertEqual(len(mock_run.call_args_list), 2)
+        mount_call_str = str(mock_run.call_args_list[1])
+        self.assertTrue(mount_call_str.startswith("call(['guestmount'"))
+        self.assertEqual(len(mock_unmount.call_args_list), 1)
+        unmount_call_str = str(mock_unmount.call_args_list[0])
+        self.assertTrue(unmount_call_str.startswith("call(['fusermount'"))
+        self.assertFalse(os.path.isdir(temp_dir))
+
+    @mock.patch("pungi.util.rmtree")
+    @mock.patch("os.listdir", new=fake_listdir("guestfs", OSError("No such file")))
+    @mock.patch('pungi.util.run_unmount_cmd')
+    @mock.patch('pungi.wrappers.iso.run')
+    def test_guestmount_handles_missing_cache(self, mock_run, mock_unmount, mock_rmtree):
         # first tuple is return value for command 'which guestmount'
         # value determines type of the mount/unmount command ('0' - guestmount is available)
         # for approach as a non-root, pair commands guestmount-fusermount are used