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

[Peter Maydell <peter.maydell@linaro.org>]

On 7 December 2015 at 15:19, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> 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 asked me to apply this to master, so I have done so.

thanks
-- PMM