iso-wrapper: Add utility for mounting images

This patch refactors logic for creating a temporary mount point,
mounting an image, running arbitrary code on it, unmounting the image
and removing the mount point. It immediately uses it in the buildinstall
phase.

Similar mounting is present in product_img phase as well, but due to
different usage pattern it's not changed yet.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/phases/buildinstall.py

@@ -27,7 +27,7 @@ from productmd.images import Image
 
 from pungi.arch import get_valid_arches
 from pungi.util import get_buildroot_rpms, get_volid, get_arch_variant_data
-from pungi.util import get_file_size, get_mtime, failable, makedirs, fusermount
+from pungi.util import get_file_size, get_mtime, failable, makedirs
 from pungi.wrappers.lorax import LoraxWrapper
 from pungi.wrappers.kojiwrapper import KojiWrapper
 from pungi.wrappers import iso
@@ -267,22 +267,15 @@ def tweak_buildinstall(compose, src, dst, arch, variant, label, volid, kickstart
     for image in images:
         if not os.path.isfile(image):
             continue
-        mount_tmp_dir = compose.mkdtemp(prefix="tweak_buildinstall")
-        # use guestmount to mount the image, which doesn't require root privileges
-        # LIBGUESTFS_BACKEND=direct: running qemu directly without libvirt
-        cmd = ["LIBGUESTFS_BACKEND=direct", "guestmount", "-a", image, "-m", "/dev/sda", mount_tmp_dir]
-        run(cmd)
 
-        for config in BOOT_CONFIGS:
-            config_path = os.path.join(tmp_dir, config)
-            config_in_image = os.path.join(mount_tmp_dir, config)
+        with iso.mount(image, logger=compose._logger) as mount_tmp_dir:
+            for config in BOOT_CONFIGS:
+                config_path = os.path.join(tmp_dir, config)
+                config_in_image = os.path.join(mount_tmp_dir, config)
 
-            if os.path.isfile(config_in_image):
-                cmd = ["cp", "-v", "--remove-destination", config_path, config_in_image]
-                run(cmd)
-
-        fusermount(mount_tmp_dir)
-        shutil.rmtree(mount_tmp_dir)
+                if os.path.isfile(config_in_image):
+                    cmd = ["cp", "-v", "--remove-destination", config_path, config_in_image]
+                    run(cmd)
 
     # HACK: make buildinstall files world readable
     run("chmod -R a+rX %s" % pipes.quote(tmp_dir))

pungi/wrappers/iso.py

@@ -18,8 +18,10 @@ import os
 import sys
 import pipes
 from fnmatch import fnmatch
+import contextlib
 
 from kobo.shortcuts import force_list, relative_path, run
+from pungi import util
 
 
 # HACK: define cmp in python3
@@ -392,3 +394,20 @@ def cmp_graft_points(x, y):
         return 1
 
     return cmp(x, y)
+
+
+@contextlib.contextmanager
+def mount(image, logger=None):
+    """Mount an image and make sure it's unmounted.
+
+    The yielded path will only be valid in the with block and is removed once
+    the image is unmounted.
+    """
+    # use guestmount to mount the image, which doesn't require root privileges
+    # LIBGUESTFS_BACKEND=direct: running qemu directly without libvirt
+    with util.temp_dir(prefix='iso-mount-') as mount_dir:
+        run(["LIBGUESTFS_BACKEND=direct", "guestmount", "-a", image, "-m", "/dev/sda", mount_dir])
+        try:
+            yield mount_dir
+        finally:
+            util.fusermount(mount_dir, logger=logger)

tests/test_iso_wrapper.py

@@ -37,3 +37,25 @@ class TestIsoUtils(unittest.TestCase):
         self.assertEqual(mock_run.call_args_list,
                          [mock.call(['/usr/bin/checkisomd5', '--md5sumonly', 'dummy.iso'])])
         self.assertGreater(len(logger.mock_calls), 0)
+
+    @mock.patch('pungi.util.run_unmount_cmd')
+    @mock.patch('pungi.wrappers.iso.run')
+    def test_mount_iso(self, mock_run, mock_unmount):
+        with iso.mount('dummy') as temp_dir:
+            self.assertTrue(os.path.isdir(temp_dir))
+        self.assertEqual(len(mock_run.call_args_list), 1)
+        self.assertEqual(len(mock_unmount.call_args_list), 1)
+        self.assertFalse(os.path.isdir(temp_dir))
+
+    @mock.patch('pungi.util.run_unmount_cmd')
+    @mock.patch('pungi.wrappers.iso.run')
+    def test_mount_iso_always_unmounts(self, mock_run, mock_unmount):
+        try:
+            with iso.mount('dummy') as temp_dir:
+                self.assertTrue(os.path.isdir(temp_dir))
+                raise RuntimeError()
+        except RuntimeError:
+            pass
+        self.assertEqual(len(mock_run.call_args_list), 1)
+        self.assertEqual(len(mock_unmount.call_args_list), 1)
+        self.assertFalse(os.path.isdir(temp_dir))