Migration from QEMU(v4.0) fails when using 3.1 or older machine
type. For example if one attempts to migrate
QEMU-2.12 started as
qemu-system-ppc64 -nodefaults -M pseries-2.12 -m 4096 -mem-path /tmp/
to current master, it will fail with
qemu-system-ppc64: Unknown ramblock "ppc_spapr.ram", cannot accept migration
qemu-system-ppc64: error while loading state for instance 0x0 of device 'ram'
qemu-system-ppc64: load of migration failed: Invalid argument
Caused by 900c0ba373 commit which switches main RAM allocation to
memory backends and the fact in 3.1 and older QEMU, backends used
full[***] QOM path as memory region name instead of backend's name.
That was changed after 3.1 to use prefix-less names by default
(fa0cb34d22) for new machine types.
*** effectively makes main RAM memory region names defined by
MachineClass::default_ram_id being altered with '/objects/' prefix
and therefore migration fails as old QEMU sends prefix-less
name while new QEMU expects name with prefix when using 3.1 and
older machine types.
Fix it by forcing implicit[1] memory backend to always use
prefix-less names for its memory region by setting
'x-use-canonical-path-for-ramblock-id'
property to false.
1) i.e. memory backend created by compat glue which maps
-m/-mem-path/-mem-prealloc/default RAM size into
appropriate backend type/options to match old CLI format.
Fixes: 900c0ba373
Signed-off-by: Igor Mammedov <imamm...@redhat.com>
Reported-by: Lukáš Doktor <ldok...@redhat.com>
---
CC: ldok...@redhat.com
CC: marcandre.lur...@redhat.com
CC: dgilb...@redhat.com
---
softmmu/vl.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 5549f4b619..1101b1cb41 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2800,6 +2800,9 @@ static void create_default_memdev(MachineState *ms, const
char *path)
object_property_set_int(obj, ms->ram_size, "size", &error_fatal);
object_property_add_child(object_get_objects_root(), mc->default_ram_id,
obj, &error_fatal);
+ /* Ensure backend's memory region name is equal to mc->default_ram_id */
+ object_property_set_bool(obj, false,
"x-use-canonical-path-for-ramblock-id",
+ &error_fatal);
user_creatable_complete(USER_CREATABLE(obj), &error_fatal);
object_unref(obj);
object_property_set_str(OBJECT(ms), mc->default_ram_id, "memory-backend",
--
2.18.1
