Re: [Qemu-devel] [PATCH] virtio-scsi: fix object check failure

["Andreas Färber" <afaerber@suse.de>]

Am 18.06.2014 14:13, schrieb Ming Lei:
> In case of vhost-scsi, the object type of VirtIODevice isn't
> VirtIOSCSI, so use the cast trick to fix the problem like
> in virtio_scsi_handle_cmd()
> 
> Cc: qemu-stable@nongnu.org
> Cc: Anthony Liguori <aliguori@amazon.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
>  hw/scsi/virtio-scsi.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index b0d7517..13700f5 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -538,7 +538,7 @@ static void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice *dev,
>  
>  static void virtio_scsi_handle_event(VirtIODevice *vdev, VirtQueue *vq)
>  {
> -    VirtIOSCSI *s = VIRTIO_SCSI(vdev);
> +    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
>  
>      if (s->events_dropped) {

If s is not of type VirtIOSCSI as you indicate, then you shouldn't be
accessing its fields here either. You're basically disabling the safety
mechanism to avoid just that.

If you see a direct cast used elsewhere, it is most likely for
performance reasons, not for correctness.

Regards,
Andreas

>          virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
> 


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