qemu-iotests: fix pylint 2.8 consider-using-with error

pylint 2.8 introduces consider-using-with error, suggesting
to use the 'with' block statement when possible.

Modify all subprocess.Popen call to use the 'with' statement,
except the one in __init__ of QemuIoInteractive class, since
it is assigned to a class field and used in other methods.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210510190449.65948-1-eesposit@redhat.com>
[mreitz: Disable bad-option-value warning in the iotests' pylintrc, so
         that disabling consider-using-with in QemuIoInteractive will
         not produce a warning in pre-2.8 pylint versions]
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/iotests.py

@@ -112,15 +112,14 @@ def qemu_tool_pipe_and_status(tool: str, args: Sequence[str],
     Run a tool and return both its output and its exit code
     """
     stderr = subprocess.STDOUT if connect_stderr else None
-    subp = subprocess.Popen(args,
-                            stdout=subprocess.PIPE,
-                            stderr=stderr,
-                            universal_newlines=True)
-    output = subp.communicate()[0]
-    if subp.returncode < 0:
-        cmd = ' '.join(args)
-        sys.stderr.write(f'{tool} received signal {-subp.returncode}: {cmd}\n')
-    return (output, subp.returncode)
+    with subprocess.Popen(args, stdout=subprocess.PIPE,
+                          stderr=stderr, universal_newlines=True) as subp:
+        output = subp.communicate()[0]
+        if subp.returncode < 0:
+            cmd = ' '.join(args)
+            sys.stderr.write(f'{tool} received signal \
+                               {-subp.returncode}: {cmd}\n')
+        return (output, subp.returncode)
 
 def qemu_img_pipe_and_status(*args: str) -> Tuple[str, int]:
     """
@@ -236,6 +235,9 @@ def qemu_io_silent_check(*args):
 class QemuIoInteractive:
     def __init__(self, *args):
         self.args = qemu_io_args_no_fmt + list(args)
+        # We need to keep the Popen objext around, and not
+        # close it immediately. Therefore, disable the pylint check:
+        # pylint: disable=consider-using-with
         self._p = subprocess.Popen(self.args, stdin=subprocess.PIPE,
                                    stdout=subprocess.PIPE,
                                    stderr=subprocess.STDOUT,
@@ -309,22 +311,22 @@ def qemu_nbd_popen(*args):
     cmd.extend(args)
 
     log('Start NBD server')
-    p = subprocess.Popen(cmd)
-    try:
-        while not os.path.exists(pid_file):
-            if p.poll() is not None:
-                raise RuntimeError(
-                    "qemu-nbd terminated with exit code {}: {}"
-                    .format(p.returncode, ' '.join(cmd)))
+    with subprocess.Popen(cmd) as p:
+        try:
+            while not os.path.exists(pid_file):
+                if p.poll() is not None:
+                    raise RuntimeError(
+                        "qemu-nbd terminated with exit code {}: {}"
+                        .format(p.returncode, ' '.join(cmd)))
 
-            time.sleep(0.01)
-        yield
-    finally:
-        if os.path.exists(pid_file):
-            os.remove(pid_file)
-        log('Kill NBD server')
-        p.kill()
-        p.wait()
+                time.sleep(0.01)
+            yield
+        finally:
+            if os.path.exists(pid_file):
+                os.remove(pid_file)
+            log('Kill NBD server')
+            p.kill()
+            p.wait()
 
 def compare_images(img1, img2, fmt1=imgfmt, fmt2=imgfmt):
     '''Return True if two image files are identical'''
@@ -333,13 +335,12 @@ def compare_images(img1, img2, fmt1=imgfmt, fmt2=imgfmt):
 
 def create_image(name, size):
     '''Create a fully-allocated raw image with sector markers'''
-    file = open(name, 'wb')
-    i = 0
-    while i < size:
-        sector = struct.pack('>l504xl', i // 512, i // 512)
-        file.write(sector)
-        i = i + 512
-    file.close()
+    with open(name, 'wb') as file:
+        i = 0
+        while i < size:
+            sector = struct.pack('>l504xl', i // 512, i // 512)
+            file.write(sector)
+            i = i + 512
 
 def image_size(img):
     '''Return image's virtual size'''

tests/qemu-iotests/pylintrc

@@ -19,6 +19,9 @@ disable=invalid-name,
         too-many-public-methods,
         # pylint warns about Optional[] etc. as unsubscriptable in 3.9
         unsubscriptable-object,
+        # Sometimes we need to disable a newly introduced pylint warning.
+        # Doing so should not produce a warning in older versions of pylint.
+        bad-option-value,
         # These are temporary, and should be removed:
         missing-docstring,
         too-many-return-statements,

tests/qemu-iotests/testrunner.py

@@ -246,17 +246,17 @@ class TestRunner(ContextManager['TestRunner']):
 
         t0 = time.time()
         with f_bad.open('w', encoding="utf-8") as f:
-            proc = subprocess.Popen(args, cwd=str(f_test.parent), env=env,
-                                    stdout=f, stderr=subprocess.STDOUT)
-            try:
-                proc.wait()
-            except KeyboardInterrupt:
-                proc.terminate()
-                proc.wait()
-                return TestResult(status='not run',
-                                  description='Interrupted by user',
-                                  interrupted=True)
-            ret = proc.returncode
+            with subprocess.Popen(args, cwd=str(f_test.parent), env=env,
+                                  stdout=f, stderr=subprocess.STDOUT) as proc:
+                try:
+                    proc.wait()
+                except KeyboardInterrupt:
+                    proc.terminate()
+                    proc.wait()
+                    return TestResult(status='not run',
+                                      description='Interrupted by user',
+                                      interrupted=True)
+                ret = proc.returncode
 
         elapsed = round(time.time() - t0, 1)