From: Jason Wang <jasowang@xxxxxxxxxx>
Date: Mon, 6 Aug 2018 11:17:47 +0800
> We use to have message like:
>
> struct vhost_msg {
> int type;
> union {
> struct vhost_iotlb_msg iotlb;
> __u8 padding[64];
> };
> };
>
> Unfortunately, there will be a hole of 32bit in 64bit machine because
> of the alignment. This leads a different formats between 32bit API and
> 64bit API. What's more it will break 32bit program running on 64bit
> machine.
>
> So fixing this by introducing a new message type with an explicit
> 32bit reserved field after type like:
>
> struct vhost_msg_v2 {
> __u32 type;
> __u32 reserved;
> union {
> struct vhost_iotlb_msg iotlb;
> __u8 padding[64];
> };
> };
>
> We will have a consistent ABI after switching to use this. To enable
> this capability, introduce a new ioctl (VHOST_SET_BAKCEND_FEATURE) for
> userspace to enable this feature (VHOST_BACKEND_F_IOTLB_V2).
>
> Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> Changes from V1:
> - use __u32 instead of int for type
Applied, thanks Jason.
