Re: [PATCH v2 07/21] qom/object: introduce user interaction flags for properties

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Feb 10, 2026 at 11:23:34AM +0800, Zhao Liu wrote:
> Introduce three new flags to `ObjectPropertyFlags` to better manage
> property interactions with external users (CLI, QMP, HMP):
> 
> 1. OBJ_PROP_FLAG_USER_SET:
>    Marks a property as having been modified by an external user.
> 
>    This flag is designed to be "sticky": once set, it persists even if
>    the property value is subsequently overwritten by internal logic.
>    It allows the QEMU system to distinguish user intent.
> 
>    The advantage of this design is that it is not needed to manually
>    clear the USER_SET flag on every internal write. This simplifies the
>    logic and decouples flag management from the current property setting
>    path (object_property_set()).
> 
>    This is chosen over a strict "current origin" approach (where
>    internal writes would clear the flag) for a practical reason: QEMU
>    code often modifies underlying struct fields (which are defined as
>    properties) directly, bypassing the property API entirely. This makes
>    it impossible to "accurately" track whether the *current* value truly
>    comes from the user. Therefore, a sticky "user touched this" flag is
>    the only meaningful and robust solution.
> 
> 2. OBJ_PROP_FLAG_DEPRECATED:
>    Marks a property as deprecated.
> 
> 3. OBJ_PROP_FLAG_INTERNAL:
>    Marks a property as internal-only, disallowing external user access.
> 
> Additionally, update object_property_set_flags() to implement the
> enforcement logic. When a property is flagged with
> OBJ_PROP_FLAG_USER_SET:
>  - If the property is also marked OBJ_PROP_FLAG_DEPRECATED, report a
>    warning.
>  - If the property is also marked OBJ_PROP_FLAG_INTERNAL, raise an error
>    and stop the operation.
> 
> Suggested-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  include/qom/object.h | 24 ++++++++++++++++++++++++
>  qom/object.c         | 15 +++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 856b12e7289c..1b77429aa28b 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -109,6 +109,30 @@ typedef enum {
>       * will automatically add a getter and a setter to this property.
>       */
>      OBJ_PROP_FLAG_READWRITE = (OBJ_PROP_FLAG_READ | OBJ_PROP_FLAG_WRITE),
> +    /*
> +     * The property was explicitly set by an external user.
> +     *
> +     * This flag is set whenever the property is modified via external interfaces
> +     * (CLI, QMP, HMP). It allows internal code to distinguish whether the
> +     * property has been modified by the user.
> +     *
> +     * Once set, this flag persists even if the property value is subsequently
> +     * overwritten by internal logic. It is NOT automatically cleared and must
> +     * be explicitly cleared using object_property_clear_flags().
> +     */
> +    OBJ_PROP_FLAG_USER_SET = BIT(2),
> +    /*
> +     * The property is deprecated and will be removed in the future version.
> +     *
> +     * Any setting to this property by the user will raise a deprecation warning.
> +     */
> +    OBJ_PROP_FLAG_DEPRECATED = BIT(3),
> +    /*
> +     * The property is internal only and cannot be set by the user.
> +     *
> +     * Any setting to this property by the user will raise an error.
> +     */
> +    OBJ_PROP_FLAG_INTERNAL = BIT(4),
>  } ObjectPropertyFlags;

I don't think this single enum design is very desirable, as it is mixing up
pieces of information with three distinct lifetimes / scopes.

The OBJ_PROP_FLAD_{READ,WRITE,READWRITE} values are scoped to the execution
of the property adder methods.

The OBJ_PROP_FLAG_{DEPRECATED,INTERNAL} values are scoped to the lifetime
of the class.

The OBJ_PROP_FLAG_USER_SET value is scoped to the lifetime of the instance.

With regards,
Daniel
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