Re: [PATCH 2/2] iotests/block-status-cache: New test

[Nir Soffer]

On Mon, Jan 17, 2022 at 6:26 PM Hanna Reitz <hreitz@redhat.com> wrote:
>
> Add a new test to verify that want_zero=false block-status calls do not
> pollute the block-status cache for want_zero=true calls.
>
> We check want_zero=true calls and their results using `qemu-img map`
> (over NBD), and want_zero=false calls also using `qemu-img map` over
> NBD, but using the qemu:allocation-depth context.
>
> (This test case cannot be integrated into nbd-qemu-allocation, because
> that is a qcow2 test, and this is a raw test.)
>
> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
> ---
>  tests/qemu-iotests/tests/block-status-cache   | 130 ++++++++++++++++++
>  .../qemu-iotests/tests/block-status-cache.out |   5 +
>  2 files changed, 135 insertions(+)
>  create mode 100755 tests/qemu-iotests/tests/block-status-cache
>  create mode 100644 tests/qemu-iotests/tests/block-status-cache.out
>
> diff --git a/tests/qemu-iotests/tests/block-status-cache 
> b/tests/qemu-iotests/tests/block-status-cache
> new file mode 100755
> index 0000000000..1f2c3109d3
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/block-status-cache
> @@ -0,0 +1,130 @@
> +#!/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_pipe, 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"""
> +        assert qemu_img_create('-f', iotests.imgfmt, test_img,
> +                               str(image_size)) == 0
> +
> +        assert qemu_nbd('-k', nbd_sock, '-f', iotests.imgfmt, '-t', '-A', 
> '-r',
> +                        f'--pid-file={nbd_pidfile}', test_img) == 0

This is a good place to comment that -A (or better --allocation-depth)
is required for this test.

> +
> +    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`

x-dirty-bitmap=qemu:allocation-depth looks a bit dirty to me but I guess
we don't have a better way without depending on another nbd client.

If depending on libnbd is ok, this test can be much simpler:

$ nbdinfo --map=base:allocation nbd+unix:///?socket=/tmp/nbd.sock
         0        4096    0  data
      4096  1073737728    3  hole,zero
$ nbdinfo --map=qemu:allocation-depth nbd+unix:///?socket=/tmp/nbd.sock
         0  1073741824    1  local
$ nbdinfo --map=qemu:allocation-depth nbd+unix:///?socket=/tmp/nbd.sock
         0  1073741824    1  local
$ nbdinfo --map=base:allocation nbd+unix:///?socket=/tmp/nbd.sock
         0  1073741824    0  data

> +        (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_pipe('map', '--output=json', '--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.

Interesting, but once we fix the bug this complex flow is gone so
we can eliminate this text, no?

> +        #
> +        # 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_pipe('map', '--output=json', '--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_pipe('map', '--output=json', '--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'])
> diff --git a/tests/qemu-iotests/tests/block-status-cache.out 
> b/tests/qemu-iotests/tests/block-status-cache.out
> new file mode 100644
> index 0000000000..ae1213e6f8
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/block-status-cache.out
> @@ -0,0 +1,5 @@
> +.
> +----------------------------------------------------------------------
> +Ran 1 tests
> +
> +OK
> --
> 2.33.1
>

Reviewed-by: Nir Soffer <nsoffer@redhat.com>