Re: [PATCH 17/22] iotests: Add VM.assert_block_path()

[Max Reitz <mreitz@redhat.com>]

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On 26.09.19 16:07, Vladimir Sementsov-Ogievskiy wrote:
> 20.09.2019 18:27, Max Reitz wrote:
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   tests/qemu-iotests/iotests.py | 48 +++++++++++++++++++++++++++++++++++
>>   1 file changed, 48 insertions(+)
>>
>> diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
>> index daed4ee013..e6fb46287d 100644
>> --- a/tests/qemu-iotests/iotests.py
>> +++ b/tests/qemu-iotests/iotests.py
>> @@ -670,6 +670,54 @@ class VM(qtest.QEMUQtestMachine):
>>   
>>           return fields.items() <= ret.items()
>>   
>> +    '''
>> +    @path is a string whose components are separated by slashes.
>> +    The first component is a node name, the rest are child names.
>> +    Examples:
>> +      - "qcow2-node/backing/file"
>> +      - "quorum-node/children.2/file"
> 
> Possibly, separting node-name to first parameter and keeping child-path as
> a second will simplify code a bit, and be more useful for cases when on caller
> part node-name is in variable.

Sounds good.

>> +
>> +    @expected_node may be None.
>> +
>> +    @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, path, expected_node, graph=None):
>> +        if graph is None:
>> +            graph = self.qmp('x-debug-query-block-graph')['return']
> 
> Yay! I'm happy to see that it's useful.

:-)

It’s probably the best query function we have.

>> +
>> +        iter_path = iter(path.split('/'))
>> +        root = next(iter_path)
>> +        try:
>> +            node = next(node for node in graph['nodes'] if node['name'] == root)
>> +        except StopIteration:
>> +            node = None
> 
> for such usage next has second optional argument: next(iterator[, default])

Great!

> (don't think I teach you Python, actually you teach me, as before I didn't know
> correct way to search first element with condition)

We learn from one another, which is the best case.

>> +
>> +        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)
> 
> Hmm here you allow default StopIteration exception [1]
> 
> 
>> +
>> +                node = next(node for node in graph['nodes'] \
>> +                                 if node['id'] == node_id)
>> +            except StopIteration:
>> +                node = None
> 
> actually, I think this will never happen, so we may simplify code and allow it to
> throw StopIteration exception in this impossible case..

This is for a use case where the next child simply doesn’t exist, so you
can do:

assert_block_path('qcow2-node/backing', None)

To verify that the qcow2 node has no backing file.

>> +
>> +        assert node is not None or expected_node is None, \
>> +               'No node found under %s (but expected %s)' % \
>> +               (path, expected_node)
> 
> node may be None here only from last iteration, but it can't happen: if we have edge
> with child, we'll for sure have node with such node-name in graph

node will always be set by the try-except block, won’t it?

>> +
>> +        assert expected_node is not None or node is None, \
>> +               'Found node %s under %s (but expected none)' % \
>> +               (node['name'], path)
> 
> hmm, so expected_node=None means we want to prove that there is no such node? It should
> be mentioned in comment above the function. But this don't work due to [1]

Hm, I seem to remember I tested all cases locally and they all worked.

Max

>> +
>> +        if node is not None and expected_node is not None:
>> +            assert node['name'] == expected_node, \
>> +                   'Found node %s under %s (but expected %s)' % \
>> +                   (node['name'], path, expected_node)
>>   
>>   index_re = re.compile(r'([^\[]+)\[([^\]]+)\]')
>>   
>>
> 
> 



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