Re: [Qemu-devel] [PATCH v2] xen_disk: add discard support

[Stefano Stabellini]

On Thu, 6 Feb 2014, Olaf Hering wrote:
> @@ -253,6 +254,8 @@ static int ioreq_parse(struct ioreq *ioreq)
>      case BLKIF_OP_WRITE:
>          ioreq->prot = PROT_READ; /* from memory */
>          break;
> +    case BLKIF_OP_DISCARD:
> +        return 0;
>      default:
>          xen_be_printf(&blkdev->xendev, 0, "error: unknown operation (%d)\n",
>                        ioreq->req.operation);

Unfortunately I didn't realize before that older Xen releases don't
define BLKIF_OP_DISCARD, therefore this patch would cause QEMU build
failures against Xen 4.1 for example.
Give a look at include/hw/xen/xen_common.h to see how compatibility
with older Xen versions is usually achieved in QEMU.