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 <[email protected]>
> Signed-off-by: Zhao Liu <[email protected]>
> ---
> 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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