test/py: regenerate persistent GPT image if code changes

test_gpt generates a persistent disk image which can be re-used across
multiple test runs. Currently, if the Python code that generates the disk
image change, the image is not regenerated, which could cause test
failures e.g. if a test was updated to expect some new partition name or
size, yet the persistent disk image contained the old name or size. This
change introduces functionality to regenerate the disk image if the
instructions to generate the image have changed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

test/py/tests/test_gpt.py

@@ -32,23 +32,24 @@ class GptTestDiskImage(object):
         persistent = u_boot_console.config.persistent_data_dir + '/' + filename
         self.path = u_boot_console.config.result_dir  + '/' + filename
 
-        if os.path.exists(persistent):
-            u_boot_console.log.action('Disk image file ' + persistent +
-                ' already exists')
-        else:
-            u_boot_console.log.action('Generating ' + persistent)
-            fd = os.open(persistent, os.O_RDWR | os.O_CREAT)
-            os.ftruncate(fd, 4194304)
-            os.close(fd)
-            cmd = ('sgdisk', '-U', '375a56f7-d6c9-4e81-b5f0-09d41ca89efe',
-                persistent)
-            u_boot_utils.run_and_log(u_boot_console, cmd)
-            cmd = ('sgdisk', '--new=1:2048:2560', '-c 1:part1', persistent)
-            u_boot_utils.run_and_log(u_boot_console, cmd)
-            cmd = ('sgdisk', '--new=2:4096:4608', '-c 2:part2', persistent)
-            u_boot_utils.run_and_log(u_boot_console, cmd)
-            cmd = ('sgdisk', '-l', persistent)
-            u_boot_utils.run_and_log(u_boot_console, cmd)
+        with u_boot_utils.persistent_file_helper(u_boot_console.log, persistent):
+            if os.path.exists(persistent):
+                u_boot_console.log.action('Disk image file ' + persistent +
+                    ' already exists')
+            else:
+                u_boot_console.log.action('Generating ' + persistent)
+                fd = os.open(persistent, os.O_RDWR | os.O_CREAT)
+                os.ftruncate(fd, 4194304)
+                os.close(fd)
+                cmd = ('sgdisk', '-U', '375a56f7-d6c9-4e81-b5f0-09d41ca89efe',
+                    persistent)
+                u_boot_utils.run_and_log(u_boot_console, cmd)
+                cmd = ('sgdisk', '--new=1:2048:2560', '-c 1:part1', persistent)
+                u_boot_utils.run_and_log(u_boot_console, cmd)
+                cmd = ('sgdisk', '--new=2:4096:4608', '-c 2:part2', persistent)
+                u_boot_utils.run_and_log(u_boot_console, cmd)
+                cmd = ('sgdisk', '-l', persistent)
+                u_boot_utils.run_and_log(u_boot_console, cmd)
 
         cmd = ('cp', persistent, self.path)
         u_boot_utils.run_and_log(u_boot_console, cmd)

test/py/u_boot_utils.py

@@ -5,6 +5,7 @@
 # Utility code shared across multiple tests.
 
 import hashlib
+import inspect
 import os
 import os.path
 import pytest
@@ -237,3 +238,76 @@ def find_ram_base(u_boot_console):
             raise Exception('Failed to find RAM bank start in `bdinfo`')
 
     return ram_base
+
+class PersistentFileHelperCtxMgr(object):
+    """A context manager for Python's "with" statement, which ensures that any
+    generated file is deleted (and hence regenerated) if its mtime is older
+    than the mtime of the Python module which generated it, and gets an mtime
+    newer than the mtime of the Python module which generated after it is
+    generated. Objects of this type should be created by factory function
+    persistent_file_helper rather than directly."""
+
+    def __init__(self, log, filename):
+        """Initialize a new object.
+
+        Args:
+            log: The Logfile object to log to.
+            filename: The filename of the generated file.
+
+        Returns:
+            Nothing.
+        """
+
+        self.log = log
+        self.filename = filename
+
+    def __enter__(self):
+        frame = inspect.stack()[1]
+        module = inspect.getmodule(frame[0])
+        self.module_filename = module.__file__
+        self.module_timestamp = os.path.getmtime(self.module_filename)
+
+        if os.path.exists(self.filename):
+            filename_timestamp = os.path.getmtime(self.filename)
+            if filename_timestamp < self.module_timestamp:
+                self.log.action('Removing stale generated file ' +
+                    self.filename)
+                os.unlink(self.filename)
+
+    def __exit__(self, extype, value, traceback):
+        if extype:
+            try:
+                os.path.unlink(self.filename)
+            except:
+                pass
+            return
+        logged = False
+        for i in range(20):
+            filename_timestamp = os.path.getmtime(self.filename)
+            if filename_timestamp > self.module_timestamp:
+                break
+            if not logged:
+                self.log.action(
+                    'Waiting for generated file timestamp to increase')
+                logged = True
+            os.utime(self.filename)
+            time.sleep(0.1)
+
+def persistent_file_helper(u_boot_log, filename):
+    """Manage the timestamps and regeneration of a persistent generated
+    file. This function creates a context manager for Python's "with"
+    statement
+
+    Usage:
+        with persistent_file_helper(u_boot_console.log, filename):
+            code to generate the file, if it's missing.
+
+    Args:
+        u_boot_log: u_boot_console.log.
+        filename: The filename of the generated file.
+
+    Returns:
+        A context manager object.
+    """
+
+    return PersistentFileHelperCtxMgr(u_boot_log, filename)