Re: [PATCH for-5.0 v2 18/23] iotests: Add VM.assert_block_path()

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

09.12.2019 18:10, Max Reitz wrote:
> On 03.12.19 13:59, Vladimir Sementsov-Ogievskiy wrote:
>> 11.11.2019 19:02, Max Reitz wrote:
>>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>>> ---
>>>    tests/qemu-iotests/iotests.py | 59 +++++++++++++++++++++++++++++++++++
>>>    1 file changed, 59 insertions(+)
>>>
>>> diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
>>> index d34305ce69..3e03320ce3 100644
>>> --- a/tests/qemu-iotests/iotests.py
>>> +++ b/tests/qemu-iotests/iotests.py
>>> @@ -681,6 +681,65 @@ class VM(qtest.QEMUQtestMachine):
>>>    
>>>            return fields.items() <= ret.items()
>>>    
>>> +    """
>>> +    Check whether the node under the given path in the block graph is
>>> +    @expected_node.
>>> +
>>> +    @root is the node name of the node where the @path is rooted.
>>> +
>>> +    @path is a string that consists of child names separated by
>>> +    slashes.  It must begin with a slash.
>>
>> Why do you need this slash?
> 
> I don’t.  It just looked better to me.
> 
> (One reason would be so it could be empty to refer to @root, but as I
> said that isn’t very useful.)
> 
>> To stress that we are starting from root?
>> But root is not global, it's selected by previous argument, so for me the
>> path is more like relative than absolute..
>>
>>> +
>>> +    Examples for @root + @path:
>>> +      - root="qcow2-node", path="/backing/file"
>>> +      - root="quorum-node", path="/children.2/file"
>>> +
>>> +    Hypothetically, @path could be empty, in which case it would point
>>> +    to @root.  However, in practice this case is not useful and hence
>>> +    not allowed.
>>
>> 1. path can't be empty, as accordingly to previous point, it must start with '/'
> 
> Hence “hypothetically”.
> 
>> 2. path can be '/', which does exactly what you don't allow, and I don't see,
>> where it is restricted in code
> 
> No, it doesn’t.  That refers to a child of @root with an empty name.

Hmm, yes, OK.

> 
>>> +
>>> +    @expected_node may be None.
>>
>> Which means that, we assert existence of the path except its last element,
>> yes? Worth mention this behavior here.
> 
> “(All elements of the path but the leaf must still exist.)”?  OK.

OK

> 
>>> +
>>> +    @graph may be None or the result of an x-debug-query-block-graph
>>> +    call that has already been performed.
>>> +    """
>>> +    def assert_block_path(self, root, path, expected_node, graph=None):
>>> +        if graph is None:
>>> +            graph = self.qmp('x-debug-query-block-graph')['return']
>>> +
>>> +        iter_path = iter(path.split('/'))
>>> +
>>> +        # Must start with a /
>>> +        assert next(iter_path) == ''
>>> +
>>> +        node = next((node for node in graph['nodes'] if node['name'] == root),
>>> +                    None)
>>> +
>>> +        for path_node in iter_path:
>>> +            assert node is not None, 'Cannot follow path %s' % path
>>> +
>>> +            try:
>>> +                node_id = next(edge['child'] for edge in graph['edges'] \
>>> +                                             if edge['parent'] == node['id'] and
>>> +                                                edge['name'] == path_node)
>>> +
>>> +                node = next(node for node in graph['nodes'] \
>>> +                                 if node['id'] == node_id)
>>
>> this line cant fail. If it fail, it means a bug in x-debug-query-block-graph, so,
>> I'd prefer to move it out of try:except block.
> 
> But that makes the code uglier, in my opinion.  We’d then have to set
> node_id to e.g. None in the except branch (or rather just abolish the
> try-except then) and check whether it’s None before assigning node.
> Like this:
> 
> node_id = next(..., None)
> 
> if node_id is not None:
>      node = next(...)
> else:
>      node = None
> 
> I prefer the current try-except construct over that.

OK

> 
>>> +            except StopIteration:
>>> +                node = None
>>> +
>>> +        assert node is not None or expected_node is None, \
>>> +               'No node found under %s (but expected %s)' % \
>>> +               (path, expected_node)
>>> +
>>> +        assert expected_node is not None or node is None, \
>>> +               'Found node %s under %s (but expected none)' % \
>>> +               (node['name'], path)
>>> +
>>> +        if node is not None and expected_node is not None:
>>
>> [1]
>> second part of condition already asserted by previous assertion
> 
> Yes, but I wanted to cover all four cases explicitly.  (In the usual 00,
> 01, 10, 11 manner.  Well, except it’s 10, 01, 11, 00.)
> 
>>> +            assert node['name'] == expected_node, \
>>> +                   'Found node %s under %s (but expected %s)' % \
>>> +                   (node['name'], path, expected_node)
>>
>> IMHO, it would be easier to read like:
>>
>>             if node is None:
>>                 assert  expected_node is None, \
>>                    'No node found under %s (but expected %s)' % \
>>                    (path, expected_node)
>>             else:
>>                 assert expected_node is not None, \
>>                    'Found node %s under %s (but expected none)' % \
>>                    (node['name'], path)
>>
>>                 assert node['name'] == expected_node, \
>>                        'Found node %s under %s (but expected %s)' % \
>>                        (node['name'], path, expected_node)
>>
>> Or even just
>>
>>             if node is None:
>>                 assert expected_node is None, \
>>                    'No node found under %s (but expected %s)' % \
>>                    (path, expected_node)
>>             else:
>>                 assert node['name'] == expected_node, \
>>                        'Found node %s under %s (but expected %s)' % \
>>                        (node['name'], path, expected_node)
> 
> Works for me, too.
> 
>> (I've checked:
>>   >>> 'erger %s erg' % None
>> 'erger None erg'
>>
>> Also, %-style formatting is old, as I understand it's better always use .format()
>> )
> 
> OK.
> 
> Max
> 
>>>    
>>>    index_re = re.compile(r'([^\[]+)\[([^\]]+)\]')
>>>    
>>>
> 
> 


-- 
Best regards,
Vladimir