block-backend: Always notify on blk_eject

blk_eject is only used by scsi-disk and atapi, and in both cases we
only attempt to invoke blk_eject if we have a bona-fide change in
tray state.

The "issue" here is that the tray state does not generate a QMP event
unless there is a medium/BDS attached to the device, so if libvirt et al
are waiting for a tray event to occur from an empty-but-closed drive,
software opening that drive will not emit an event and libvirt will
wait forever.

Change this by modifying blk_eject to always emit an event, instead of
conditionally on a "real" backend eject.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1373264
Reported-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1478553214-497-2-git-send-email-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

diff --git a/block/block-backend.c b/block/block-backend.c
index 27a7f6f523b775fcde0e5fb83638074228171adf..efbf398bb54d68d8b1a2f5823cbaf2affc91b66e 100644 (file)
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1393,13 +1393,14 @@ void blk_eject(BlockBackend *blk, bool eject_flag)
 
     if (bs) {
         bdrv_eject(bs, eject_flag);
-
-        id = blk_get_attached_dev_id(blk);
-        qapi_event_send_device_tray_moved(blk_name(blk), id,
-                                          eject_flag, &error_abort);
-        g_free(id);
-
     }
+
+    /* Whether or not we ejected on the backend,
+     * the frontend experienced a tray event. */
+    id = blk_get_attached_dev_id(blk);
+    qapi_event_send_device_tray_moved(blk_name(blk), id,
+                                      eject_flag, &error_abort);
+    g_free(id);
 }
 
 int blk_get_flags(BlockBackend *blk)