[RFC PATCH v2 02/20] hw/core/qdev: Add vmstate_qdev_no_state_to_migrate

[Philippe Mathieu-Daudé]

Add vmstate_qdev_no_state_to_migrate, which is simply a
pointer to vmstate_no_state_to_migrate. This way all
qdev devices (including "hw/qdev-core.h") don't have to
include "migration/vmstate.h".

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Unresolved issues:

https://www.mail-archive.com/qemu-devel@nongnu.org/msg721695.html
Peter:
> Does this definitely not put any data into the migration stream?
> We don't want to change what's on the wire for machines that
> use devices that start using this. (If it does by default, it
> would be easy to make the migration code special case the
> magic symbol to act like "no vmsd specified").

https://www.mail-archive.com/qemu-devel@nongnu.org/msg727634.html
Dave:
> I'd need to test it to be sure, but I think if we added a .needed
> to vmstate_no_state_to_migrate with a function that always returned
> false, then I think the stream would stay unchanged.
---
 include/hw/qdev-core.h      | 2 ++
 include/migration/vmstate.h | 1 +
 hw/core/qdev.c              | 3 +++
 migration/vmstate.c         | 7 +++++++
 stubs/vmstate.c             | 7 +++++++
 5 files changed, 20 insertions(+)

diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index bafc311bfa1..d2c7a46e6a2 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -140,6 +140,8 @@ struct DeviceClass {
     const char *bus_type;
 };
 
+extern const VMStateDescription *vmstate_qdev_no_state_to_migrate;
+
 typedef struct NamedGPIOList NamedGPIOList;
 
 struct NamedGPIOList {
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index dda65c9987d..50559598eac 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -197,6 +197,7 @@ struct VMStateDescription {
 #if defined(CONFIG_USER_ONLY)
 extern const VMStateDescription vmstate_user_mode_cpu_dummy;
 #endif
+extern const VMStateDescription vmstate_no_state_to_migrate;
 
 extern const VMStateInfo vmstate_info_bool;
 
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index cefc5eaa0a9..f0d0afd438d 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -44,6 +44,9 @@
 static bool qdev_hot_added = false;
 bool qdev_hot_removed = false;
 
+const VMStateDescription *vmstate_qdev_no_state_to_migrate =
+        &vmstate_no_state_to_migrate;
+
 const VMStateDescription *qdev_get_vmsd(DeviceState *dev)
 {
     DeviceClass *dc = DEVICE_GET_CLASS(dev);
diff --git a/migration/vmstate.c b/migration/vmstate.c
index 05f87cdddc5..2c373774dfa 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -20,6 +20,13 @@
 #include "qemu/error-report.h"
 #include "trace.h"
 
+const VMStateDescription vmstate_no_state_to_migrate = {
+    .name = "empty-state",
+    .fields = (VMStateField[]) {
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
                                    void *opaque, JSONWriter *vmdesc);
 static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
diff --git a/stubs/vmstate.c b/stubs/vmstate.c
index 8da777a1fb4..f561f9f39bd 100644
--- a/stubs/vmstate.c
+++ b/stubs/vmstate.c
@@ -5,6 +5,13 @@
 const VMStateDescription vmstate_user_mode_cpu_dummy = {};
 #endif
 
+const VMStateDescription vmstate_no_state_to_migrate = {
+    .name = "empty-state",
+    .fields = (VMStateField[]) {
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 int vmstate_register_with_alias_id(VMStateIf *obj,
                                    uint32_t instance_id,
                                    const VMStateDescription *vmsd,
-- 
2.26.2