Re: [PATCH hci-8.0 1/5] iotests: add coverage for NBD transmission commands #VSTOR-119829

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

On 8/31/26 6:25 PM, Denis V. Lunev wrote:
> From: Denis V. Lunev <den@openvz.org>
> 
> NBD_CMD_CACHE has no coverage anywhere in the tree. Nothing ever
> sends it: our own NBD client does not implement the command, and
> neither qemu-io nor 'qemu-nbd --list' can issue one, so the only
> clients reaching this server path are external ones.
> 
> Add a test driven by libnbd, gated the way nbd-multiconn already is,
> and start it with the case the command exists for. The export is a
> qcow2 image over a fully written backing file, so a prefetch has
> visible work to do.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Eric Blake <eblake@redhat.com>
> Message-ID: <20260827161002.310688-2-den@openvz.org>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  tests/qemu-iotests/tests/nbd-commands     | 140 ++++++++++++++++++++++
>  tests/qemu-iotests/tests/nbd-commands.out |   5 +
>  2 files changed, 145 insertions(+)
>  create mode 100755 tests/qemu-iotests/tests/nbd-commands
>  create mode 100644 tests/qemu-iotests/tests/nbd-commands.out
> 
> diff --git a/tests/qemu-iotests/tests/nbd-commands b/tests/qemu-iotests/tests/nbd-commands
> new file mode 100755
> index 00000000000..4c1cd33db74
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/nbd-commands
> @@ -0,0 +1,140 @@
> +#!/usr/bin/env python3
> +# group: rw auto quick
> +#
> +# Test NBD transmission commands against a qemu NBD export
> +#
> +# Copyright (C) 2026 Virtuozzo International GmbH
> +#
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +
> +import os
> +from types import ModuleType
> +
> +import iotests
> +from iotests import qemu_img_create, qemu_img_map, qemu_io
> +
> +
> +base = os.path.join(iotests.test_dir, 'base')
> +top = os.path.join(iotests.test_dir, 'top')
> +# Larger than the maximum payload size an export can advertise
> +size = 64 * 1024 * 1024
> +pattern = 0xa5
> +nbd_sock = os.path.join(iotests.sock_dir, 'nbd_sock')
> +nbd_uri = 'nbd+unix:///exp?socket=' + nbd_sock
> +nbd: ModuleType
> +
> +DEPTH_LOCAL = 1
> +DEPTH_BACKING = 2
> +
> +
> +class TestNbdCommands(iotests.QMPTestCase):
> +    def setUp(self):
> +        qemu_img_create('-f', iotests.imgfmt, base, str(size))
> +        qemu_io('-c', f'write -P {pattern} 0 {size}', base)
> +        qemu_img_create('-f', iotests.imgfmt, '-b', base,
> +                        '-F', iotests.imgfmt, top, str(size))
> +
> +        self.vm = iotests.VM()
> +        self.vm.launch()
> +        self.vm.cmd('blockdev-add', {
> +            'driver': iotests.imgfmt,
> +            'node-name': 'n',
> +            'file': {'driver': 'file', 'filename': top},
> +            'backing': {
> +                'driver': iotests.imgfmt,
> +                'node-name': 'base',
> +                'file': {'driver': 'file', 'filename': base},
> +            },
> +        })
> +        self.vm.cmd('nbd-server-start', {
> +            'addr': {'type': 'unix', 'data': {'path': nbd_sock}}
> +        })
> +        self.vm.cmd('block-export-add', {
> +            'type': 'nbd',
> +            'id': 'exp',
> +            'node-name': 'n',
> +            'name': 'exp',
> +            'writable': True,
> +            'allocation-depth': True,
> +        })
> +
> +        self.h = None
> +        self.connect()
> +
> +    def tearDown(self):
> +        self.disconnect()
> +        self.vm.shutdown()
> +        for f in (top, base, nbd_sock):
> +            try:
> +                os.remove(f)
> +            except OSError:
> +                pass
> +
> +    def connect(self, structured=True, extended=True):
> +        self.disconnect()
> +        h = nbd.NBD()
> +        h.set_request_structured_replies(structured)
> +        h.set_request_extended_headers(extended)
> +        h.add_meta_context('base:allocation')
> +        h.add_meta_context('qemu:allocation-depth')
> +        # Let the server, not libnbd, reject the out of range requests below
> +        h.set_strict_mode(h.get_strict_mode() &
> +                          ~(nbd.STRICT_BOUNDS | nbd.STRICT_PAYLOAD))
> +        h.connect_uri(nbd_uri)
> +        self.assertEqual(h.get_structured_replies_negotiated(), structured)
> +        self.assertEqual(h.get_extended_headers_negotiated(), extended)
> +        self.h = h
> +
> +    def disconnect(self):
> +        if self.h is not None:
> +            self.h.shutdown()
> +            self.h = None
> +
> +    def block_status(self, count=size):
> +        """Map each meta context in the reply to its list of extents."""
> +        reply = {}
> +
> +        def cb(meta, _offset, entries, _err):
> +            reply.setdefault(meta, []).extend(zip(entries[0::2],
> +                                                  entries[1::2]))
> +
> +        self.h.block_status(count, 0, cb)
> +        return reply
> +
> +    def top_extents(self):
> +        """Which parts of the top image are local, once qemu has let go."""
> +        self.disconnect()
> +        self.vm.shutdown()
> +        return [(e['start'], e['length'], e['depth'])
> +                for e in qemu_img_map(top)]
This test is broken in our downstream because of commit ce4a1338cf7
("block/io: copy-on-read: use aio task pool").  The test fails flakily.
Namely we get on qemu_img_map():

OK run:
  {start: 0,        length: 33554432, depth: 0, offset:   327680}
  {start: 33554432, length: 33554432, depth: 1, offset: 33882112}

FAIL run:
  {start: 0,        length: 16777216, depth: 0, offset: 17104896}
  {start: 16777216, length: 16777216, depth: 0, offset:   327680}
  {start: 33554432, length: 33554432, depth: 1, offset: 33882112}

I.e. it's same data, but cluster allocation order is broken.  I'll send
a follow up fix.

Andrey