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

[Max Reitz <mreitz@redhat.com>]

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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.

>> +
>> +    @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.

>> +
>> +    @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.

>> +            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'([^\[]+)\[([^\]]+)\]')
>>   
>>



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