[PATCH v3 07/28] hw/xen: use correct default protocol for xen-block on x86

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

Even on x86_64 the default protocol is the x86-32 one if the guest doesn't
specifically ask for x86-64.

Fixes: b6af8926fb85 ("xen: add implementations of xen-block connect and disconnect functions...")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 hw/block/xen-block.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index a07cd7eb5d..64470fc579 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -117,7 +117,11 @@ static void xen_block_connect(XenDevice *xendev, Error **errp)
 
     if (xen_device_frontend_scanf(xendev, "protocol", "%ms",
                                   &str) != 1) {
-        protocol = BLKIF_PROTOCOL_NATIVE;
+        /* x86 defaults to the 32-bit protocol even for 64-bit guests. */
+        if (object_dynamic_cast(OBJECT(qdev_get_machine()), "x86-machine"))
+            protocol = BLKIF_PROTOCOL_X86_32;
+        else
+            protocol = BLKIF_PROTOCOL_NATIVE;
     } else {
         if (strcmp(str, XEN_IO_PROTO_ABI_X86_32) == 0) {
             protocol = BLKIF_PROTOCOL_X86_32;
-- 
2.40.1