Re: [PATCH v2 3/6] qdev-monitor: add option to report GenericError from find_device_state

[Vladimir Sementsov-Ogievskiy]

On 07.03.24 12:46, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
>
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> > ---
> >   system/qdev-monitor.c | 15 +++++++++++----
> >   1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> > index 9febb743f1..cf7481e416 100644
> > --- a/system/qdev-monitor.c
> > +++ b/system/qdev-monitor.c
> > @@ -877,13 +877,20 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, 
> > Error **errp)
> >       object_unref(OBJECT(dev));
> >   }
> >   
> > -static DeviceState *find_device_state(const char *id, Error **errp)
> > +/*
> > + * Note that creating new APIs using error classes other than GenericError is
> > + * not recommended. Set use_generic_error=true for new interfaces.
> > + */
> > +static DeviceState *find_device_state(const char *id, bool use_generic_error,
> > +                                      Error **errp)
> >   {
> >       Object *obj = object_resolve_path_at(qdev_get_peripheral(), id);
> >       DeviceState *dev;
> >   
> >       if (!obj) {
> > -        error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
> > +        error_set(errp,
> > +                  (use_generic_error ?
> > +                   ERROR_CLASS_GENERIC_ERROR : ERROR_CLASS_DEVICE_NOT_FOUND),
> >                     "Device '%s' not found", id);
> >           return NULL;
> >       }
> > @@ -947,7 +954,7 @@ void qdev_unplug(DeviceState *dev, Error **errp)
> >   
> >   void qmp_device_del(const char *id, Error **errp)
> >   {
> > -    DeviceState *dev = find_device_state(id, errp);
> > +    DeviceState *dev = find_device_state(id, false, errp);
> >       if (dev != NULL) {
> >           if (dev->pending_deleted_event &&
> >               (dev->pending_deleted_expires_ms == 0 ||
> > @@ -1067,7 +1074,7 @@ BlockBackend *blk_by_qdev_id(const char *id, Error **errp)
> >   
> >       GLOBAL_STATE_CODE();
> >   
> > -    dev = find_device_state(id, errp);
> > +    dev = find_device_state(id, false, errp);
> >       if (dev == NULL) {
> >           return NULL;
> >       }
>
> I appreciate the attempt to curb the spread of DeviceNotFound errors.
> Two issues:
>
> * Copy-pasting find_device_state() with a false argument is an easy
>    error to make.
>
> * Most uses of find_device_state() are via blk_by_qdev_id() and
>    qmp_get_blk().  Any new uses of qemu_get_blk() will still produce
>    DeviceNotFound.

Hm. But what to do?

- rename all three functions to FOO_base(), and add a boolean parameter
- add FOO() wrappers, passing true (use generic error)
- add FOO_deprecated() wrappers, passing false (use device not found error)
- change existing callers to use FOO_deprecated()

Still, new generic-error-based blk_by_qdev_id() and qmp_get_blk() will be 
unused..

That seem too ugly for me. And that doesn't give 100% sure that nobody will 
simply duplicate call to _deprecated() function...

Maybe better don't care for now (and continue use device-not-found for new 
APIs, that reuse find_device_state()), and just declare the deprecation for 
ERROR_CLASS_DEVICE_NOT_FOUND? And drop it usage everywhere after 3-releases 
deprecation cycle.

Or do we want deprecate everything except for generic-error, and deprecate 
error/class field in qmp return value altogether?

--
Best regards,
Vladimir