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 09:49:40AM +0000, Daniel P. Berrangé wrote:
> 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.

In fact, with my comment on the later patch, OBJ_PROP_FLAG_DEPRECATED should
not be modelled as a boolean flag at all.  We need to record a const char*
deprecation_note internally, so that warn_report can provide useful info
to the user. We can turn that into a "bool deprecated" flag in the QAPI
command response for querying properties.


With regards,
Daniel
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