fw_cfg: add API to find FW cfg object

Remove some code duplication by adding a
function to look up the fw cfg file.
This way, we don't need to duplicate same strings everywhere.
Use by both fw cfg and pvpanic device.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/misc/pvpanic.c

@@ -96,7 +96,7 @@ static int pvpanic_isa_initfn(ISADevice *dev)
     isa_register_ioport(dev, &s->io, s->ioport);
 
     if (!port_configured) {
-        fw_cfg = object_resolve_path("/machine/fw_cfg", NULL);
+        fw_cfg = fw_cfg_find();
         if (fw_cfg) {
             fw_cfg_add_file(fw_cfg, "etc/pvpanic-port",
                             g_memdup(&s->ioport, sizeof(s->ioport)),

hw/nvram/fw_cfg.c

@@ -32,6 +32,9 @@
 
 #define FW_CFG_SIZE 2
 #define FW_CFG_DATA_SIZE 1
+#define TYPE_FW_CFG "fw_cfg"
+#define FW_CFG_NAME "fw_cfg"
+#define FW_CFG_PATH "/machine/" FW_CFG_NAME
 
 typedef struct FWCfgEntry {
     uint32_t len;
@@ -493,8 +496,8 @@ FWCfgState *fw_cfg_init(uint32_t ctl_port, uint32_t data_port,
 
     s = DO_UPCAST(FWCfgState, busdev.qdev, dev);
 
-    if (!object_resolve_path("/machine/fw_cfg", NULL)) {
-        object_property_add_child(qdev_get_machine(), "fw_cfg", OBJECT(s),
+    if (!object_resolve_path(FW_CFG_PATH, NULL)) {
+        object_property_add_child(qdev_get_machine(), FW_CFG_NAME, OBJECT(s),
                                   NULL);
     }
 
@@ -553,6 +556,12 @@ static Property fw_cfg_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+FWCfgState *fw_cfg_find(void)
+{
+    return OBJECT_CHECK(FWCfgState, object_resolve_path(FW_CFG_PATH, NULL),
+                        TYPE_FW_CFG);
+}
+
 static void fw_cfg_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -566,7 +575,7 @@ static void fw_cfg_class_init(ObjectClass *klass, void *data)
 }
 
 static const TypeInfo fw_cfg_info = {
-    .name          = "fw_cfg",
+    .name          = TYPE_FW_CFG,
     .parent        = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(FWCfgState),
     .class_init    = fw_cfg_class_init,

include/hw/nvram/fw_cfg.h

@@ -73,6 +73,8 @@ void fw_cfg_add_file(FWCfgState *s, const char *filename, void *data,
 FWCfgState *fw_cfg_init(uint32_t ctl_port, uint32_t data_port,
                         hwaddr crl_addr, hwaddr data_addr);
 
+FWCfgState *fw_cfg_find(void);
+
 #endif /* NO_QEMU_PROTOS */
 
 #endif