[RFC PATCH v1 19/25] hw/xen: Only advertise ring-page-order for xen-block if gnttab supports it

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

Whem emulating Xen, multi-page grants are distinctly non-trivial and we
have elected not to support them for the time being. Don't advertise
them to the guest.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 hw/block/xen-block.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 87299615e3..f5a744589d 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -83,7 +83,8 @@ static void xen_block_connect(XenDevice *xendev, Error **errp)
             g_free(ring_ref);
             return;
         }
-    } else if (order <= blockdev->props.max_ring_page_order) {
+    } else if (qemu_xen_gnttab_can_map_multi() &&
+               order <= blockdev->props.max_ring_page_order) {
         unsigned int i;
 
         nr_ring_ref = 1 << order;
@@ -255,8 +256,12 @@ static void xen_block_realize(XenDevice *xendev, Error 
**errp)
     }
 
     xen_device_backend_printf(xendev, "feature-flush-cache", "%u", 1);
-    xen_device_backend_printf(xendev, "max-ring-page-order", "%u",
-                              blockdev->props.max_ring_page_order);
+
+    if (qemu_xen_gnttab_can_map_multi()) {
+        xen_device_backend_printf(xendev, "max-ring-page-order", "%u",
+                                  blockdev->props.max_ring_page_order);
+    }
+
     xen_device_backend_printf(xendev, "info", "%u", blockdev->info);
 
     xen_device_frontend_printf(xendev, "virtual-device", "%lu",
-- 
2.39.0