iotests.py: Add (verify|has)_working_luks()

Similar to _require_working_luks for bash tests, these functions can be
used to check whether our luks driver can actually create images.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200625125548.870061-6-mreitz@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

tests/qemu-iotests/iotests.py

@@ -1052,6 +1052,45 @@ def verify_quorum():
     if not supports_quorum():
         notrun('quorum support missing')
 
+def has_working_luks() -> Tuple[bool, str]:
+    """
+    Check whether our LUKS driver can actually create images
+    (this extends to LUKS encryption for qcow2).
+
+    If not, return the reason why.
+    """
+
+    img_file = f'{test_dir}/luks-test.luks'
+    (output, status) = \
+        qemu_img_pipe_and_status('create', '-f', 'luks',
+                                 '--object', luks_default_secret_object,
+                                 '-o', luks_default_key_secret_opt,
+                                 '-o', 'iter-time=10',
+                                 img_file, '1G')
+    try:
+        os.remove(img_file)
+    except OSError:
+        pass
+
+    if status != 0:
+        reason = output
+        for line in output.splitlines():
+            if img_file + ':' in line:
+                reason = line.split(img_file + ':', 1)[1].strip()
+                break
+
+        return (False, reason)
+    else:
+        return (True, '')
+
+def verify_working_luks():
+    """
+    Skip test suite if LUKS does not work
+    """
+    (working, reason) = has_working_luks()
+    if not working:
+        notrun(reason)
+
 def qemu_pipe(*args):
     """
     Run qemu with an option to print something and exit (e.g. a help option).