[Qemu-devel] [PATCH for-2.8 1/2] monitor: fix object_del for command-line-created objects

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Currently objects specified on the command-line are only partially
cleaned up when 'object_del' is issued in either HMP or QMP: the
object itself is fully finalized, but the QemuOpts are not removed.
This results in the following behavior:

  x86_64-softmmu/qemu-system-x86_64 -monitor stdio \
    -object memory-backend-ram,id=ram1,size=256M

  QEMU 2.7.91 monitor - type 'help' for more information
  (qemu) object_del ram1
  (qemu) object_del ram1
  object 'ram1' not found
  (qemu) object_add memory-backend-ram,id=ram1,size=256M
  Duplicate ID 'ram1' for object
  Try "help object_add" for more information

which can be an issue for use-cases like memory hotplug.

This happens on the HMP side because hmp_object_add() attempts to
create a temporary QemuOpts entry with ID 'ram1', which ends up
conflicting with the command-line-created entry, since it was never
cleaned up during the previous hmp_object_del() call.

We address this by adding a check in user_creatable_del(), which
is called by both qmp_object_del() and hmp_object_del() to handle
the actual object cleanup, to determine whether an option group entry
matching the object's ID is present and removing it if it is.

Note that qmp_object_add() never attempts to create a temporary
QemuOpts entry, so it does not encounter the duplicate ID error,
which is why this isn't generally visible in libvirt.

Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Daniel Berrange <berrange@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 qom/object_interfaces.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
index ded4d84..23849f9 100644
--- a/qom/object_interfaces.c
+++ b/qom/object_interfaces.c
@@ -5,6 +5,7 @@
 #include "qapi-visit.h"
 #include "qapi/qobject-output-visitor.h"
 #include "qapi/opts-visitor.h"
+#include "qemu/config-file.h"
 
 void user_creatable_complete(Object *obj, Error **errp)
 {
@@ -197,6 +198,7 @@ void user_creatable_del(const char *id, Error **errp)
 {
     Object *container;
     Object *obj;
+    QemuOptsList *opt_group;
 
     container = object_get_objects_root();
     obj = object_resolve_path_component(container, id);
@@ -209,6 +211,15 @@ void user_creatable_del(const char *id, Error **errp)
         error_setg(errp, "object '%s' is in use, can not be deleted", id);
         return;
     }
+
+    /* if object was defined on the command-line, remove its corresponding
+     * option group entry
+     */
+    opt_group = qemu_find_opts_err("object", NULL);
+    if (opt_group) {
+        qemu_opts_del(qemu_opts_find(opt_group, id));
+    }
+
     object_unparent(obj);
 }
 
-- 
1.9.1