Open Stack

Hi Rui,

The problem with the following rule is that there are a bunch of hidden
variables in the "not cinder:volumes(...)" literal.  The error message
shows the hidden variables.  The syntax restriction is that every variable
in a negative literal must appear in a positive literal in the body.  Those
hidden variables fail to satisfy that restriction, hence the error.

 error(id) :- cinder:volumes(id=id), not cinder:volumes(id=id,
status="available")

The reason the other rule worked is that you made the hidden variables
equivalent to the ones in the positive literal, e.g. x_0_1 shows up in both
the positive and negative literals.

error(x) :- cinder:volumes(x, _x_0_1, _x_0_2, _x_0_3, _x_0_4, _x_0_5,
_x_0_6, _x_0_7, _x_0_8),not cinder:volumes(x, _x_0_1, _x_0_2,
\"available\",_x_0_4, _x_0_5, _x_0_6, _x_0_7, _x_0_8)

But in the auto-generated one, the variables in the two literals are
different e.g. _x_0_1 and _x_1_1

error(id) :- cinder:volumes(id, _x_0_1, _x_0_2, _x_0_3, _x_0_4, _x_0_5,
_x_0_6, _x_0_7, _x_0_8), not cinder:volumes(id, _x_1_1, _x_1_2,
"available", _x_1_4, _x_1_5, _x_1_6, _x_1_7, _x_1_8).  Unsafe lits: not
cinder:volumes(id, _x_1_1, _x_1_2, "available", _x_1_4, _x_1_5, _x_1_6,
_x_1_7, _x_1_8)

Probably the solution you want is to write 2 rules:

error(id) :- cinder:volumes(id=id), not avail_cinder_vol(id)
avail_cinder_vol(id) :- cinder:volumes(id=id, status="available")

Tim

On Thu, Aug 13, 2015 at 8:07 PM Rui Chen <chenrui.momo at gmail.com> wrote:

> Sorry, send the same mail again, please comments at here, the other mail
> lack title.
>
> 2015-08-14 11:03 GMT+08:00 Rui Chen <chenrui.momo at gmail.com>:
>
>> Hi folks:
>>
>>     I face a problem when I insert a rule into Congress. I want to find
>> out all of the volumes that are not available status, so I draft a rule
>> like this:
>>
>>     error(id) :- cinder:volumes(id=id), not cinder:volumes(id=id,
>> status="available")
>>
>>     But when I create the rule, a error is raised:
>>
>> (openstack) congress policy rule create chenrui_p "error(id) :-
>> cinder:volumes(id=id),not cinder:volumes(id=id, status=\"available\")"
>> ERROR: openstack Syntax error for rule::Errors: Could not reorder rule
>> error(id) :- cinder:volumes(id, _x_0_1, _x_0_2, _x_0_3, _x_0_4, _x_0_5,
>> _x_0_6, _x_0_7, _x_0_8), not cinder:volumes(id, _x_1_1, _x_1_2,
>> "available", _x_1_4, _x_1_5, _x_1_6, _x_1_7, _x_1_8).  Unsafe lits: not
>> cinder:volumes(id, _x_1_1, _x_1_2, "available", _x_1_4, _x_1_5, _x_1_6,
>> _x_1_7, _x_1_8) (vars set(['_x_1_2', '_x_1_1', '_x_1_6', '_x_1_7',
>> '_x_1_4', '_x_1_5', '_x_1_8'])) (HTTP 400) (Request-ID:
>> req-1f4432d6-f869-472b-aa7d-4cf78dd96fa1)
>>
>>     I check the Congress policy docs [1], looks like that the rule don't
>> break any syntax restrictions.
>>
>>     If I modify the rule like this, it works:
>>
>> (openstack) congress policy rule create chenrui_p "error(x) :-
>> cinder:volumes(x, _x_0_1, _x_0_2, _x_0_3, _x_0_4, _x_0_5, _x_0_6, _x_0_7,
>> _x_0_8),not cinder:volumes(x, _x_0_1, _x_0_2, \"available\",_x_0_4, _x_0_5,
>> _x_0_6, _x_0_7, _x_0_8)"
>>
>> +---------+------------------------------------------------------------------------------------------------+
>> | Field   | Value
>>                                  |
>>
>> +---------+------------------------------------------------------------------------------------------------+
>> | comment | None
>>                                   |
>> | id      | ad121e09-ba0a-45d6-bd18-487d975d5bf5
>>                                   |
>> | name    | None
>>                                   |
>> | rule    | error(x) :-
>>                                  |
>> |         |     cinder:volumes(x, _x_0_1, _x_0_2, _x_0_3, _x_0_4, _x_0_5,
>> _x_0_6, _x_0_7, _x_0_8),         |
>> |         |     not cinder:volumes(x, _x_0_1, _x_0_2, "available",
>> _x_0_4, _x_0_5, _x_0_6, _x_0_7, _x_0_8) |
>>
>> +---------+------------------------------------------------------------------------------------------------+
>>
>>     I'm not sure this is a bug or I miss something from docs, so I need
>> some feedback from mail list.
>> Feel free to discuss about it.
>>
>>
>> [1]:
>> http://congress.readthedocs.org/en/latest/policy.html#datalog-syntax-restrictions
>>
>>
>> Best Regards.
>>
>
> __________________________________________________________________________
> OpenStack Development Mailing List (not for usage questions)
> Unsubscribe: OpenStack-dev-request at lists.openstack.org?subject:unsubscribe
> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20150814/6ae9047c/attachment.html>