Re: [Qemu-devel] [PATCH] virtio-blk: Drop x-data-plane option

[Paolo Bonzini <pbonzini@redhat.com>]

On 07/12/2015 14:02, Fam Zheng wrote:
> On Mon, 12/07 12:29, Cornelia Huck wrote:
>> On Mon,  7 Dec 2015 18:59:27 +0800
>> Fam Zheng <famz@redhat.com> wrote:
>>
>>> The official way of enabling dataplane is through the "iothread"
>>> property that references an iothread object created by "-object
>>> iothread".  Since the old "x-data-plane=on" way now even crashes, it's
>>> probably easier to just drop it:
>>>
>>> $ qemu-system-x86_64 -drive file=null-co://,id=d0,if=none \
>>>     -device virtio-blk-pci,drive=d0,x-data-plane=on
>>>
>>> ERROR:/home/fam/work/qemu/qom/object.c:1515:
>>> object_get_canonical_path_component: assertion failed: (obj->parent != NULL)
>>> Aborted
>>
>> Do we understand yet why this crashes, btw?
> 
> I think it's because with x-data-plane=on, virtio-blk initialize an object that
> doesn't have a parent, therefore it doesn't have a valid "canonical path
> component" thing, which is different from objects created with "-object" CLI.
> I'm not very familiar with the QOM semantics here.
> 
>>
>>>
>>> Signed-off-by: Fam Zheng <famz@redhat.com>
>>> ---
>>>  hw/block/dataplane/virtio-blk.c | 15 ++-------------
>>>  hw/block/virtio-blk.c           |  1 -
>>>  include/hw/virtio/virtio-blk.h  |  1 -
>>>  3 files changed, 2 insertions(+), 15 deletions(-)
>>>
>>
>> No general objection to removing x-data-plane; but this probably wants
>> a mention on the changelog as x-data-plane has been described in
>> various howtos etc. over the years.
> 
> Yes, that is a good point.  I don't know if it's too rushing in removing it for
> 2.5 (this is just posted as one option) and we'll have to count on QOM experts
> for the fix, if it is.

The solution would be to add object_property_add_child to
virtio_blk_data_plane_create, between object_initialize and
user_creatable_complete.  But I think this patch is ok for 2.5.

Paolo