Re: [Qemu-devel] [PATCH 01/10] virtio: move VirtQueueElement at the beginning of the structs

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/01/2016 13:09, Cornelia Huck wrote:
>> > The next patch will make virtqueue_pop/vring_pop allocate memory for a
> s/will make/will make it possible for/
> 
> ?

This patch will actually do that.  This patch makes it possible.

> I had to spend some time grepping through the code to find that blk and
> scsi (and gpu, which already had elem at the beginning of its
> structure) are the only ones that work like this and that other devices
> do not need any change.
> 
>> > "subclass" of VirtQueueElement.  For this to work, VirtQueueElement
>> > must be the first field in the containing struct.

So...

The next patch will make virtqueue_pop/vring_pop allocate memory for the
VirtQueueElement.  In some cases (blk, scsi, gpu) the device wants to
extend VirtQueueElement with device-specific fields and, until now, the
place of the VirtQueueElement within the containing struct didn't
matter.  When allocating the entire block in virtqueue_pop/vring_pop,
however, the containing struct must basically be a "subclass" of
VirtQueueElement, with the VirtQueueElement as the first field.  Make
that the case for blk and scsi; gpu is already doing it.

Paolo

>> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> > ---
>> >  hw/scsi/virtio-scsi.c           |  3 +--
>> >  include/hw/virtio/virtio-blk.h  |  2 +-
>> >  include/hw/virtio/virtio-scsi.h | 13 ++++++-------
>> >  3 files changed, 8 insertions(+), 10 deletions(-)
> Otherwise,
> 
> Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> 
> 
>