tests: addressed feedback

will squash with the previous commits.

Signed-off-by: Kazuyoshi Kato <[email protected]>

Author: kzys

tests/integration_tests/functional/test_drives.py

@@ -4,7 +4,7 @@
 
 import os
 import platform
-from subprocess import run, CalledProcessError
+from subprocess import run, CalledProcessError, PIPE
 
 import pytest
 
@@ -92,14 +92,14 @@ def test_rescan_dev(test_microvm_with_ssh, network_config):
         size=512
     )
 
-    # "losetup --find" may slow down tests due to
-    # https://github.com/firecracker-microvm/firecracker-containerd/issues/141
-    loopback_device = f'/dev/loop{os.getpid()}'
-    losetup = ['losetup', loopback_device, fs2.path]
+    losetup = ['losetup', '--find', '--show', fs2.path]
+    loopback_device = None
     try:
-        run(losetup, check=True)
-    except CalledProcessError:
-        pytest.skip("the kernel doesn't have enough loopback devices")
+        result = run(losetup, check=True, stdout=PIPE, stderr=PIPE)
+        loopback_device = result.stdout.decode('utf-8').rstrip()
+    except CalledProcessError as error:
+        pytest.skip('failed to create a lookback device: ' +
+                    f'stdout={error.stdout}, stderr={error.stderr}')
 
     try:
         response = test_microvm.drive.patch(
@@ -110,7 +110,8 @@ def test_rescan_dev(test_microvm_with_ssh, network_config):
 
         _check_scratch_size(ssh_connection, fs2.size())
     finally:
-        run(['losetup', '-d', loopback_device], check=True)
+        if loopback_device:
+            run(['losetup', '--detach', loopback_device], check=True)
 
 
 def test_non_partuuid_boot(test_microvm_with_ssh, network_config):