tests/qemu-iotests/tests/block-status-cache

#!/usr/bin/env python3
# group: rw quick
#
# Test cases for the block-status cache.
#
# 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 os
import signal
import iotests
from iotests import qemu_img_create, qemu_img_map, qemu_nbd


image_size = 1 * 1024 * 1024
test_img = os.path.join(iotests.test_dir, 'test.img')

nbd_pidfile = os.path.join(iotests.test_dir, 'nbd.pid')
nbd_sock = os.path.join(iotests.sock_dir, 'nbd.sock')


class TestBscWithNbd(iotests.QMPTestCase):
    def setUp(self) -> None:
        """Just create an empty image with a read-only NBD server on it"""
        qemu_img_create('-f', iotests.imgfmt, test_img, str(image_size))

        # Pass --allocation-depth to enable the qemu:allocation-depth context,
        # which we are going to query to provoke a block-status inquiry with
        # want_zero=false.
        assert qemu_nbd(f'--socket={nbd_sock}',
                        f'--format={iotests.imgfmt}',
                        '--persistent',
                        '--allocation-depth',
                        '--read-only',
                        f'--pid-file={nbd_pidfile}',
                        test_img) \
            == 0

    def tearDown(self) -> None:
        with open(nbd_pidfile, encoding='utf-8') as f:
            pid = int(f.read())
        os.kill(pid, signal.SIGTERM)
        os.remove(nbd_pidfile)
        os.remove(test_img)

    def test_with_zero_bug(self) -> None:
        """
        Verify that the block-status cache is not corrupted by a
        want_zero=false call.
        We can provoke a want_zero=false call with `qemu-img map` over NBD with
        x-dirty-bitmap=qemu:allocation-depth, so we first run a normal `map`
        (which results in want_zero=true), then using said
        qemu:allocation-depth context, and finally another normal `map` to
        verify that the cache has not been corrupted.
        """

        nbd_img_opts = f'driver=nbd,server.type=unix,server.path={nbd_sock}'
        nbd_img_opts_alloc_depth = nbd_img_opts + \
            ',x-dirty-bitmap=qemu:allocation-depth'

        # Normal map, results in want_zero=true.
        # This will probably detect an allocated data sector first (qemu likes
        # to allocate the first sector to facilitate alignment probing), and
        # then the rest to be zero.  The BSC will thus contain (if anything)
        # one range covering the first sector.
        map_pre = qemu_img_map('--image-opts', nbd_img_opts)

        # qemu:allocation-depth maps for want_zero=false.
        # want_zero=false should (with the file driver, which the server is
        # using) report everything as data.  While this is sufficient for
        # want_zero=false, this is nothing that should end up in the
        # block-status cache.
        # Due to a bug, this information did end up in the cache, though, and
        # this would lead to wrong information being returned on subsequent
        # want_zero=true calls.
        #
        # We need to run this map twice: On the first call, we probably still
        # have the first sector in the cache, and so this will be served from
        # the cache; and only the subsequent range will be queried from the
        # block driver.  This subsequent range will then be entered into the
        # cache.
        # If we did a want_zero=true call at this point, we would thus get
        # correct information: The first sector is not covered by the cache, so
        # we would get fresh block-status information from the driver, which
        # would return a data range, and this would then go into the cache,
        # evicting the wrong range from the want_zero=false call before.
        #
        # Therefore, we need a second want_zero=false map to reproduce:
        # Since the first sector is not in the cache, the query for its status
        # will go to the driver, which will return a result that reports the
        # whole image to be a single data area.  This result will then go into
        # the cache, and so the cache will then report the whole image to
        # contain data.
        #
        # Note that once the cache reports the whole image to contain data, any
        # subsequent map operation will be served from the cache, and so we can
        # never loop too many times here.
        for _ in range(2):
            # (Ignore the result, this is just to contaminate the cache)
            qemu_img_map('--image-opts', nbd_img_opts_alloc_depth)

        # Now let's see whether the cache reports everything as data, or
        # whether we get correct information (i.e. the same as we got on our
        # first attempt).
        map_post = qemu_img_map('--image-opts', nbd_img_opts)

        if map_pre != map_post:
            print('ERROR: Map information differs before and after querying ' +
                  'qemu:allocation-depth')
            print('Before:')
            print(map_pre)
            print('After:')
            print(map_post)

            self.fail("Map information differs")


if __name__ == '__main__':
    # The block-status cache only works on the protocol layer, so to test it,
    # we can only use the raw format
    iotests.main(supported_fmts=['raw'],
                 supported_protocols=['file'])