monitor: allow device_del to accept QOM paths

Currently device_del requires that the client provide the
device short ID. device_add allows devices to be created
without giving an ID, at which point there is no way to
delete them with device_del. The QOM object path, however,
provides an alternative way to identify the devices.

Allowing device_del to accept an object path ensures all
devices are deletable regardless of whether they have an
ID.

 (qemu) device_add usb-mouse
 (qemu) qom-list /machine/peripheral-anon
 device[0] (child<usb-mouse>)
 type (string)
 (qemu) device_del /machine/peripheral-anon/device[0]

Devices are required to be marked as hotpluggable
otherwise an error is raised

 (qemu) device_del /machine/unattached/device[4]
 Device 'PIIX3' does not support hotplugging

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1441974836-17476-1-git-send-email-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[Commit message touched up, accidental white-space change dropped]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

hmp-commands.hx

@@ -676,7 +676,8 @@ ETEXI
 STEXI
 @item device_del @var{id}
 @findex device_del
-Remove device @var{id}.
+Remove device @var{id}. @var{id} may be a short ID
+or a QOM object path.
 ETEXI
 
     {

qapi-schema.json

@@ -1951,7 +1951,7 @@
 #
 # Remove a device from a guest
 #
-# @id: the name of the device
+# @id: the name or QOM path of the device
 #
 # Returns: Nothing on success
 #          If @id is not a valid device, DeviceNotFound

qdev-monitor.c

@@ -771,12 +771,17 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
 void qmp_device_del(const char *id, Error **errp)
 {
     Object *obj;
-    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);
+    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);
+    }
 
     if (!obj) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
@@ -784,6 +789,11 @@ void qmp_device_del(const char *id, Error **errp)
         return;
     }
 
+    if (!object_dynamic_cast(obj, TYPE_DEVICE)) {
+        error_setg(errp, "%s is not a hotpluggable device", id);
+        return;
+    }
+
     qdev_unplug(DEVICE(obj), errp);
 }
 

qmp-commands.hx

@@ -321,13 +321,18 @@ Remove a device.
 
 Arguments:
 
-- "id": the device's ID (json-string)
+- "id": the device's ID or QOM path (json-string)
 
 Example:
 
 -> { "execute": "device_del", "arguments": { "id": "net1" } }
 <- { "return": {} }
 
+Example:
+
+-> { "execute": "device_del", "arguments": { "id": "/machine/peripheral-anon/device[0]" } }
+<- { "return": {} }
+
 EQMP
 
     {