Re: [PATCH] qom: Allow object_property_add_child() to fail

[Daniel P . Berrangé]

On Wed, Jun 24, 2020 at 10:22:14AM +0200, Markus Armbruster wrote:
> Eric Auger <eric.auger@redhat.com> writes:
> 
> > object_property_add() does not allow object_property_try_add()
> > to gracefully fail as &error_abort is passed as an error handle.
> >
> > However such failure can easily be triggered from the QMP shell when,
> > for instance, one attempts to create an object with an id that already
> > exists:
> >
> > For instance, call twice:
> > object-add qom-type=memory-backend-ram id=mem1 props.size=1073741824
> > and QEMU aborts.
> >
> > This behavior is undesired as a user/management application mistake
> > in reusing a property ID shouldn't result in loss of the VM and live
> > data within.
> >
> > This patch introduces two new functions, object_property_add_err() and
> > object_property_add_child_err() whose prototype features an error handle.
> > object_property_add_child_err() now gets called from 
> > user_creatable_add_type.
> > This solution was chosen instead of changing the prototype of existing
> > functions because the number of existing callers is huge.
> >
> > The error now is returned gracefully to the QMP client.
> >
> > (QEMU) object-add qom-type=memory-backend-ram id=mem2  props.size=4294967296
> > {"return": {}}
> > (QEMU) object-add qom-type=memory-backend-ram id=mem2  props.size=4294967296
> > {"error": {"class": "GenericError", "desc": "attempt to add duplicate 
> > property
> > 'mem2' to object (type 'container')"}}
> >
> > Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> Recent regression, my fault.  Please point that out, and add
> 
>   Fixes: d2623129a7dec1d3041ad1221dda1ca49c667532

I noticed tests/qtest/qmp-cmd-test.c exercises object-add. Probably a
good idea to extend that to test duplicate ID scenario, as that would
have caught the accidental regression.

Regards,
Daniel
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