[PATCH v2] tests/stream-under-throttle: New test

[Hanna Reitz]

Test streaming a base image into the top image underneath two throttle
nodes.  This was reported to make qemu 7.1 hang
(https://gitlab.com/qemu-project/qemu/-/issues/1215), so this serves as
a regression test.

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
---
Based-on: <20221107151321.211175-1-hreitz@redhat.com>

v1: https://lists.nongnu.org/archive/html/qemu-block/2022-11/msg00368.html

v2:
- Replace `asyncio.exceptions.TimeoutError` by `asyncio.TimeoutError`:
  Stefan reported that the CI does not recognize the former:
  https://lists.nongnu.org/archive/html/qemu-block/2022-11/msg00424.html

  As far as I understand, the latter was basically moved to become the
  former in Python 3.11, and an alias remains, so both are basically
  equivalent.  I only have 3.10, though, where the documentation says
  that both are different, even though using either seems to work fine
  (i.e. both catch the timeout there).  Not sure about previous
  versions, but the CI seems pretty certain about not knowing
  `asyncio.exceptions.TimeoutError`, so use `asyncio.TimeoutError`
  instead.  (Even though that is deprecated in 3.11, but this is not the
  first place in the tree to use it, so it should not be too bad.)
---
 .../qemu-iotests/tests/stream-under-throttle  | 121 ++++++++++++++++++
 .../tests/stream-under-throttle.out           |   5 +
 2 files changed, 126 insertions(+)
 create mode 100755 tests/qemu-iotests/tests/stream-under-throttle
 create mode 100644 tests/qemu-iotests/tests/stream-under-throttle.out

diff --git a/tests/qemu-iotests/tests/stream-under-throttle 
b/tests/qemu-iotests/tests/stream-under-throttle
new file mode 100755
index 0000000000..8d2d9e1684
--- /dev/null
+++ b/tests/qemu-iotests/tests/stream-under-throttle
@@ -0,0 +1,121 @@
+#!/usr/bin/env python3
+# group: rw
+#
+# Test streaming with throttle nodes on top
+#
+# Copyright (C) 2022 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+import asyncio
+import os
+from typing import List
+import iotests
+from iotests import qemu_img_create, qemu_io
+
+
+image_size = 256 * 1024 * 1024
+base_img = os.path.join(iotests.test_dir, 'base.img')
+top_img = os.path.join(iotests.test_dir, 'top.img')
+
+
+class TcgVM(iotests.VM):
+    '''
+    Variant of iotests.VM that uses -accel tcg.  Simply using
+    iotests.VM.add_args('-accel', 'tcg') is not sufficient, because that will
+    put -accel qtest before -accel tcg, and -accel arguments are prioritized in
+    the order they appear.
+    '''
+    @property
+    def _base_args(self) -> List[str]:
+        # Put -accel tcg first so it takes precedence
+        return ['-accel', 'tcg'] + super()._base_args
+
+
+class TestStreamWithThrottle(iotests.QMPTestCase):
+    def setUp(self) -> None:
+        '''
+        Create a simple backing chain between two images, write something to
+        the base image.  Attach them to the VM underneath two throttle nodes,
+        one of which has actually no limits set, but the other does.  Then put
+        a virtio-blk device on top.
+        This test configuration has been taken from
+        https://gitlab.com/qemu-project/qemu/-/issues/1215
+        '''
+        qemu_img_create('-f', iotests.imgfmt, base_img, str(image_size))
+        qemu_img_create('-f', iotests.imgfmt, '-b', base_img, '-F',
+                        iotests.imgfmt, top_img, str(image_size))
+
+        # Write something to stream
+        qemu_io(base_img, '-c', f'write 0 {image_size}')
+
+        blockdev = {
+            'driver': 'throttle',
+            'node-name': 'throttled-node',
+            'throttle-group': 'thrgr-limited',
+            'file': {
+                'driver': 'throttle',
+                'throttle-group': 'thrgr-unlimited',
+                'file': {
+                    'driver': iotests.imgfmt,
+                    'node-name': 'unthrottled-node',
+                    'file': {
+                        'driver': 'file',
+                        'filename': top_img
+                    }
+                }
+            }
+        }
+
+        # Issue 1215 is not reproducible in qtest mode, which is why we need to
+        # create an -accel tcg VM
+        self.vm = TcgVM()
+        self.vm.add_object('iothread,id=iothr0')
+        self.vm.add_object('throttle-group,id=thrgr-unlimited')
+        self.vm.add_object('throttle-group,id=thrgr-limited,'
+                           'x-iops-total=10000,x-bps-total=104857600')
+        self.vm.add_blockdev(self.vm.qmp_to_opts(blockdev))
+        self.vm.add_device('virtio-blk,iothread=iothr0,drive=throttled-node')
+        self.vm.launch()
+
+    def tearDown(self) -> None:
+        self.vm.shutdown()
+        os.remove(top_img)
+        os.remove(base_img)
+
+    def test_stream(self) -> None:
+        '''
+        Do a simple stream beneath the two throttle nodes.  Should complete
+        with no problems.
+        '''
+        result = self.vm.qmp('block-stream',
+                             job_id='stream',
+                             device='unthrottled-node')
+        self.assert_qmp(result, 'return', {})
+
+        # Should succeed and not time out
+        try:
+            self.vm.run_job('stream')
+        except asyncio.TimeoutError:
+            # VM may be stuck, kill it before tearDown()
+            self.vm.kill()
+            raise
+
+
+if __name__ == '__main__':
+    # Must support backing images
+    iotests.main(supported_fmts=['qcow', 'qcow2', 'qed'],
+                 supported_protocols=['file'],
+                 required_fmts=['throttle'])
diff --git a/tests/qemu-iotests/tests/stream-under-throttle.out 
b/tests/qemu-iotests/tests/stream-under-throttle.out
new file mode 100644
index 0000000000..ae1213e6f8
--- /dev/null
+++ b/tests/qemu-iotests/tests/stream-under-throttle.out
@@ -0,0 +1,5 @@
+.
+----------------------------------------------------------------------
+Ran 1 tests
+
+OK
-- 
2.36.1