ramfb: add migration support

Implementing RAMFB migration is quite straightforward. One caveat is to
treat the whole RAMFBCfg as a blob, since that's what is exposed to the
guest directly. This avoid having to fiddle with endianness issues if we
were to migrate fields individually as integers.

The devices using RAMFB will have to include ramfb_vmstate in their
migration description.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/display/ramfb.c

@@ -28,6 +28,8 @@ struct QEMU_PACKED RAMFBCfg {
     uint32_t stride;
 };
 
+typedef struct RAMFBCfg RAMFBCfg;
+
 struct RAMFBState {
     DisplaySurface *ds;
     uint32_t width, height;
@@ -116,6 +118,23 @@ void ramfb_display_update(QemuConsole *con, RAMFBState *s)
     dpy_gfx_update_full(con);
 }
 
+static int ramfb_post_load(void *opaque, int version_id)
+{
+    ramfb_fw_cfg_write(opaque, 0, 0);
+    return 0;
+}
+
+const VMStateDescription ramfb_vmstate = {
+    .name = "ramfb",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = ramfb_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_BUFFER_UNSAFE(cfg, RAMFBState, 0, sizeof(RAMFBCfg)),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 RAMFBState *ramfb_setup(Error **errp)
 {
     FWCfgState *fw_cfg = fw_cfg_find();

include/hw/display/ramfb.h

@@ -1,11 +1,15 @@
 #ifndef RAMFB_H
 #define RAMFB_H
 
+#include "migration/vmstate.h"
+
 /* ramfb.c */
 typedef struct RAMFBState RAMFBState;
 void ramfb_display_update(QemuConsole *con, RAMFBState *s);
 RAMFBState *ramfb_setup(Error **errp);
 
+extern const VMStateDescription ramfb_vmstate;
+
 /* ramfb-standalone.c */
 #define TYPE_RAMFB_DEVICE "ramfb"