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

[Markus Armbruster]

Michael Roth <address@hidden> writes:

> 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" <address@hidden>
> Cc: Markus Armbruster <address@hidden>
> Cc: Eric Blake <address@hidden>
> Cc: Daniel Berrange <address@hidden>
> Cc: address@hidden
> Signed-off-by: Michael Roth <address@hidden>
> ---
>  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) {

How can opt_group ever be null?

For what it's worth, we assume it can't in hmp_object_add() and main().

> +        qemu_opts_del(qemu_opts_find(opt_group, id));
> +    }
> +
>      object_unparent(obj);
>  }