backtrace when creating bcached partition

[Paul Collins]

When creating a new bcached partition via the MAAS UI, after I click the final "Create bcache", nothing seems to happen, except that the bcache UI, including the device I selected, disappear. But I note the following in regiond.log:

2016-04-18 02:02:02 [-] Error on request (345) node.create_bcache: <ul class="errorlist"><li>__all__<ul class="errorlist"><li>Either backing_device or backing_partition must be specified.</li></ul></li><li>backing_device<ul class="errorlist"><li>Select a valid choice. 32 is not one of the available choices.</li></ul></li></ul>
        Traceback (most recent call last):
          File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
            self.__bootstrap_inner()
          File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
            self.run()
          File "/usr/lib/python2.7/threading.py", line 763, in run
            self.__target(*self.__args, **self.__kwargs)
          File "/usr/lib/python2.7/dist-packages/provisioningserver/utils/twisted.py", line 791, in _worker
            return super(ThreadPool, self)._worker()
        --- <exception caught here> ---
          File "/usr/lib/python2.7/dist-packages/twisted/python/threadpool.py", line 191, in _worker
            result = context.call(ctx, function, *args, **kwargs)
          File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 501, in call_within_transaction
            return func_outside_txn(*args, **kwargs)
          File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 328, in retrier
            return func(*args, **kwargs)
          File "/usr/lib/python2.7/dist-packages/django/db/transaction.py", line 339, in inner
            return func(*args, **kwargs)
          File "/usr/lib/python2.7/dist-packages/maasserver/websockets/handlers/node.py", line 980, in create_bcache
            raise HandlerError(form.errors)
        maasserver.websockets.base.HandlerError: <ul class="errorlist"><li>__all__<ul class="errorlist"><li>Either backing_device or backing_partition must be specified.</li></ul></li><li>backing_device<ul class="errorlist"><li>Select a valid choice. 32 is not one of the available choices.</li></ul></li></ul>

This seems similar to https://bugs.launchpad.net/maas/+bug/1547185 but it started working for the reporter of that bug later.

We are running MAAS 1.9.1+bzr4543-0ubuntu1~trusty1 from the PPA. Attached please find a screenshot just before I click the final "Create bcache" and trigger the traceback.

[Paul Collins (pjdc)]

I've discovered that if I create an unformatted partition manually, select the resulting (in this case) "sda-part3", and invoke "create bcache", then everything works fine.

I think the MAAS UI should either do this for me, or else prevent me from invoking "create bcache" on the unformatted space of a block device perhaps with some kind of hint. But the first option seems friendlier.

[Gavin Panella (allenap)]

Bug 1556963 ("HandlerError suppressed in UI") is related.

[Andres Rodriguez (andreserl)]

We believe this is no longer an issue in the latest releases of MAAS. Please upgrade to the latest version of MAAS, and If you believe this issue is still present, please re-open this bug report or file a new one.