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

[Daniel P . Berrangé]

On Tue, Jun 23, 2020 at 05:54:52PM +0200, Eric Auger wrote:
> 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>
> ---
>  include/qom/object.h    | 24 ++++++++++++++++++++++--
>  qom/object.c            | 33 ++++++++++++++++++++++++++++-----
>  qom/object_interfaces.c |  7 +++++--
>  3 files changed, 55 insertions(+), 9 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
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