monitor: Tidy up find_device_state()

Commit 6287d82 "monitor: allow device_del to accept QOM paths"
extended find_device_state() to accept QOM paths in addition to qdev
IDs.  This added a checked conversion to TYPE_DEVICE at the end, which
duplicates the check done for the qdev ID case earlier, except it sets
a *different* error: GenericError "ID is not a hotpluggable device"
when passed a QOM path, and DeviceNotFound "Device 'ID' not found"
when passed a qdev ID.  Fortunately, the latter won't happen as long
as we add only devices to /machine/peripheral/.

Earlier, commit b6cc36a "qdev: device_del: Search for to be
unplugged device in 'peripheral' container" rewrote the lookup by qdev
ID to use QOM instead of qdev_find_recursive(), so it can handle
buss-less devices.  It does so by constructing an absolute QOM path.
Works, but object_resolve_path_component() is easier.  Switching to it
also gets rid of the unclean duplication described above.

While there, avoid converting to TYPE_DEVICE twice, first to check
whether it's possible, and then for real.

Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Damien Hedde <[email protected]>
Reviewed-by: Daniel P. Berrangé <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Markus Armbruster

softmmu/qdev-monitor.c

@@ -836,16 +836,12 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
 static DeviceState *find_device_state(const char *id, Error **errp)
 {
     Object *obj;
+    DeviceState *dev;
 
     if (id[0] == '/') {
         obj = object_resolve_path(id, NULL);
     } else {
-        char *root_path = object_get_canonical_path(qdev_get_peripheral());
-        char *path = g_strdup_printf("%s/%s", root_path, id);
-
-        g_free(root_path);
-        obj = object_resolve_path_type(path, TYPE_DEVICE, NULL);
-        g_free(path);
+        obj = object_resolve_path_component(qdev_get_peripheral(), id);
     }
 
     if (!obj) {
@@ -854,12 +850,13 @@ static DeviceState *find_device_state(const char *id, Error **errp)
         return NULL;
     }
 
-    if (!object_dynamic_cast(obj, TYPE_DEVICE)) {
+    dev = (DeviceState *)object_dynamic_cast(obj, TYPE_DEVICE);
+    if (!dev) {
         error_setg(errp, "%s is not a hotpluggable device", id);
         return NULL;
     }
 
-    return DEVICE(obj);
+    return dev;
 }
 
 void qdev_unplug(DeviceState *dev, Error **errp)