dmtest: Write random data instead of zeroes to geometry block

Replaces the function that write zeroes to the vdo geometry block with
a call to write random data. Then checks for possible expected error
messages.

The new code that formats vdo devices directly in the kernel decides
whether to format by looking at the geometry block. If it is all
zeroes, the device is formatted. Therefore, we want to change this
test to write random data instead of zeroes, since we don't want to
format the device.

Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>

Author: bjohnsto

src/dmtest/assertions.py

@@ -1,3 +1,5 @@
+import re
+
 def assert_raises(callback):
     failed = False
     try:
@@ -28,3 +30,9 @@ def assert_string_in(actual, expected, message=None):
         error_message = f"{message}: " if message else ""
         error_message += f"expected '{expected}', but got {actual}"
         raise AssertionError(error_message)
+
+def assert_matches(actual, pattern, message=None):
+    if not re.search(pattern, actual):
+        error_message = f"{message}: " if message else ""
+        error_message += f"expected match for '{pattern}', but got {actual}"
+        raise AssertionError(error_message)

src/dmtest/utils.py

@@ -149,6 +149,10 @@ def wipe_device(dev, sectors=None):
     _dd_device("/dev/zero", _to_path(dev), "oflag=direct", sectors, sync=True)
 
 
+def trash_device(dev, sectors=None):
+    _dd_device("/dev/urandom", _to_path(dev), "oflag=direct", sectors, sync=True)
+
+
 def dev_size(dev):
     (_, stdout, _) = process.run(f"blockdev --getsz {_to_path(dev)}")
     return int(stdout)

src/dmtest/vdo/load_failure_tests.py

@@ -1,6 +1,6 @@
-from dmtest.assertions import assert_string_in
+from dmtest.assertions import assert_matches, assert_string_in
 from dmtest.vdo.utils import standard_vdo, standard_stack
-from dmtest.utils import get_dmesg_log, wipe_device
+from dmtest.utils import get_dmesg_log, trash_device
 import logging as log
 import time
 
@@ -52,8 +52,8 @@ def t_corrupt_geometry(fix):
     with standard_vdo(fix) as vdo:
         pass
     start_time = time.time()
-    # Trash just one (4kB) block
-    wipe_device(fix.cfg["data_dev"], 8)
+    # Overwrite just one (4kB) block with random data
+    trash_device(fix.cfg["data_dev"], 8)
     stack = standard_stack(fix, format = False)
     started = False
     try:
@@ -62,7 +62,7 @@ def t_corrupt_geometry(fix):
     except:
         message = get_dmesg_log(start_time)
         log.info(message)
-        assert_string_in(message, "Could not load geometry block")
+        assert_matches(message, r"Could not (load|parse) geometry block")
     if started:
         raise AssertionError("VDO device shouldn't have started")