Re: [PATCH v9 3/3] iotests: test nbd reconnect

[Eric Blake <eblake@redhat.com>]

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On 9/17/19 12:13 PM, Vladimir Sementsov-Ogievskiy wrote:
> Add test, which starts backup to nbd target and restarts nbd server
> during backup.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  tests/qemu-iotests/264        | 65 +++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/264.out    | 12 +++++++
>  tests/qemu-iotests/group      |  1 +
>  tests/qemu-iotests/iotests.py |  4 +++
>  4 files changed, 82 insertions(+)
>  create mode 100755 tests/qemu-iotests/264
>  create mode 100644 tests/qemu-iotests/264.out
> 

> +import time
> +
> +import iotests
> +from iotests import qemu_img_create, file_path, qemu_nbd_popen, log
> +
> +disk_a, disk_b, nbd_sock = file_path('disk_a', 'disk_b', 'nbd-sock')
> +
> +qemu_img_create('-f', iotests.imgfmt, disk_a, '5M')
> +qemu_img_create('-f', iotests.imgfmt, disk_b, '5M')
> +srv = qemu_nbd_popen('-k', nbd_sock, '-f', iotests.imgfmt, disk_b)
> +time.sleep(1)
> +

Hard-coded sleep times can be problematic (too long, and the test is no
longer quick; too short, and heavy load can interfere); is there any way
to poll for a completion event rather than just waiting one second?

> +vm = iotests.VM().add_drive(disk_a)
> +vm.launch()
> +vm.hmp_qemu_io('drive0', 'write 0 5M')
> +
> +vm.qmp_log('blockdev-add', filters=[iotests.filter_qmp_testfiles],
> +           **{'node_name': 'backup0',
> +              'driver': 'raw',
> +              'file': {'driver': 'nbd',
> +                       'server': {'type': 'unix', 'path': nbd_sock},
> +                       'reconnect-delay': 10}})
> +vm.qmp_log('blockdev-backup', device='drive0', sync='full', target='backup0',
> +           speed=(1 * 1024 * 1024))

Throttling to make sure we are likely to still be going and thus test
the reconnect logic.

> +
> +time.sleep(1)
> +log('Kill NBD server')
> +srv.kill()

Again, that hard-coded sleep looks a bit risky.

> +
> +jobs = vm.qmp('query-block-jobs')['return']
> +if jobs and jobs[0]['offset'] < jobs[0]['len']:
> +    log('Backup job is still in progress')
> +
> +time.sleep(1)

Why do we need yet another sleep?

> +
> +log('Start NBD server')
> +srv = qemu_nbd_popen('-k', nbd_sock, '-f', iotests.imgfmt, disk_b)
> +
> +vm.qmp_log('block-job-set-speed', device='drive0', speed=0)

So here, you release the throttle to finish the job.

> +e = vm.event_wait('BLOCK_JOB_COMPLETED')
> +log('Backup completed: {}'.format(e['data']['offset']))
> +
> +vm.qmp_log('blockdev-del', node_name='backup0')
> +srv.kill()
> +vm.shutdown()
> diff --git a/tests/qemu-iotests/264.out b/tests/qemu-iotests/264.out
> new file mode 100644
> index 0000000000..4a2f4aa509
> --- /dev/null
> +++ b/tests/qemu-iotests/264.out
> @@ -0,0 +1,12 @@
> +{"execute": "blockdev-add", "arguments": {"driver": "raw", "file": {"driver": "nbd", "reconnect-delay": 10, "server": {"path": "TEST_DIR/PID-nbd-sock", "type": "unix"}}, "node-name": "backup0"}}
> +{"return": {}}
> +{"execute": "blockdev-backup", "arguments": {"device": "drive0", "speed": 1048576, "sync": "full", "target": "backup0"}}
> +{"return": {}}
> +Kill NBD server
> +Backup job is still in progress
> +Start NBD server
> +{"execute": "block-job-set-speed", "arguments": {"device": "drive0", "speed": 0}}
> +{"return": {}}
> +Backup completed: 5242880
> +{"execute": "blockdev-del", "arguments": {"node-name": "backup0"}}
> +{"return": {}}
> diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
> index 5d3da937e4..4f6dd6f153 100644
> --- a/tests/qemu-iotests/group
> +++ b/tests/qemu-iotests/group
> @@ -275,5 +275,6 @@
>  258 rw quick
>  262 rw quick migration
>  263 rw quick
> +264 rw quick

With that many hard-coded sleeps, is it still quick?

/me applies the patch and runs it...

264      pass       [14:49:55] [14:50:01]   6s

that's borderline enough that I would not call it quick.

>  
> +def qemu_nbd_popen(*args):
> +    '''Run qemu-nbd in daemon mode and return the parent's exit code'''
> +    return subprocess.Popen(qemu_nbd_args + ['--persistent'] + list(args))
> +

Should you also use a pid file here, and wait for the existence of the
pid file before returning (rather than hard-coding sleep(1))?

>  def compare_images(img1, img2, fmt1=imgfmt, fmt2=imgfmt):
>      '''Return True if two image files are identical'''
>      return qemu_img('compare', '-f', fmt1,
> 

At any rate,

Tested-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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