Fix pc migration from qemu <= 1.5

The following commit introduced a migration incompatibility:

commit 568f0690fd9aa4d39d84b04c1a5dbb53a915c3fe
Author: David Gibson <david@gibson.dropbear.id.au>
Date:   Thu Jun 6 18:48:49 2013 +1000

    pci: Replace pci_find_domain() with more general pci_root_bus_path()

The issue is that i440fx savevm idstr went from 0000:00:00.0/I440FX to
0000:00.0/I440FX. Unfortunately we are stuck with the breakage for
1.6 machine types.

Add a compat property to maintain the busted idstr for the 1.6 machine
types, but revert to the old style format for 1.7+, and <= 1.5.

Tested with migration from qemu 1.5, qemu 1.6, and qemu.git.

Cc: qemu-stable@nongnu.org
Signed-off-by: Cole Robinson <crobinso@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
index b8feed1254..c043998e32 100644
--- a/hw/pci-host/q35.c
+++ b/hw/pci-host/q35.c
@@ -61,8 +61,13 @@ static void q35_host_realize(DeviceState *dev, Error **errp)
 static const char *q35_host_root_bus_path(PCIHostState *host_bridge,
                                           PCIBus *rootbus)
 {
-    /* For backwards compat with old device paths */
-    return "0000";
+    Q35PCIHost *s = Q35_HOST_DEVICE(host_bridge);
+
+     /* For backwards compat with old device paths */
+    if (s->mch.short_root_bus) {
+        return "0000";
+    }
+    return "0000:00";
 }
 
 static void q35_host_get_pci_hole_start(Object *obj, Visitor *v,
@@ -124,6 +129,7 @@ static Property mch_props[] = {
                         MCH_HOST_BRIDGE_PCIEXBAR_DEFAULT),
     DEFINE_PROP_SIZE(PCI_HOST_PROP_PCI_HOLE64_SIZE, Q35PCIHost,
                      mch.pci_hole64_size, DEFAULT_PCI_HOLE64_SIZE),
+    DEFINE_PROP_UINT32("short_root_bus", Q35PCIHost, mch.short_root_bus, 0),
     DEFINE_PROP_END_OF_LIST(),
 };