block: Add qdev ID to DEVICE_TRAY_MOVED

The event currently only contains the BlockBackend name. However, with
anonymous BlockBackends, this is always the empty string. Add the qdev
ID (or if none was given, the QOM path) so that the user can still see
which device caused the event.

Event generation has to be moved from bdrv_eject() to the BlockBackend
because the BDS doesn't know the attached device, but that's easy
because blk_eject() is the only user of it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

docs/qmp-commands.txt

@@ -3239,6 +3239,7 @@ Example:
                     "microseconds": 716996 },
      "event": "DEVICE_TRAY_MOVED",
      "data": { "device": "ide1-cd0",
+               "id": "ide0-1-0",
                "tray-open": true } }
 
 <- { "return": {} }
@@ -3267,6 +3268,7 @@ Example:
                     "microseconds": 272147 },
      "event": "DEVICE_TRAY_MOVED",
      "data": { "device": "ide1-cd0",
+               "id": "ide0-1-0",
                "tray-open": false } }
 
 <- { "return": {} }
@@ -3303,6 +3305,7 @@ Example:
                     "microseconds": 549958 },
      "event": "DEVICE_TRAY_MOVED",
      "data": { "device": "ide1-cd0",
+               "id": "ide0-1-0",
                "tray-open": true } }
 
 <- { "return": {} }

docs/qmp-events.txt

@@ -220,12 +220,16 @@ or by HMP/QMP commands.
 
 Data:
 
-- "device": device name (json-string)
+- "device": Block device name. This is always present for compatibility
+            reasons, but it can be empty ("") if the image does not have a
+            device name associated. (json-string)
+- "id": The name or QOM path of the guest device (json-string)
 - "tray-open": true if the tray has been opened or false if it has been closed
                (json-bool)
 
 { "event": "DEVICE_TRAY_MOVED",
   "data": { "device": "ide1-cd0",
+            "id": "/machine/unattached/device[22]",
             "tray-open": true
   },
   "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }