Re: [Qemu-block] [PATCH RFC v3 4/8] block: convert ThrottleGroup to object with QOM

[Stefan Hajnoczi]

On Mon, Jun 26, 2017 at 07:58:32PM +0300, Manos Pitsidianakis wrote:
> On Mon, Jun 26, 2017 at 03:52:34PM +0100, Stefan Hajnoczi wrote:
> > On Fri, Jun 23, 2017 at 03:46:56PM +0300, Manos Pitsidianakis wrote:
> > > +static bool throttle_group_exists(const char *name)
> > > +{
> > > +    ThrottleGroup *iter;
> > > +    bool ret = false;
> > > +
> > > +    qemu_mutex_lock(&throttle_groups_lock);
> > 
> > Not sure if this lock or the throttle_groups list are necessary.
> > 
> > Have you seen iothread.c:qmp_query_iothreads()?  All objects are put
> > into a container (the parent object), so you can just iterate over its
> > children.  There's no need for a separate list because QOM already has
> > all the objects.
> > 
> 
> > > +static void throttle_group_obj_complete(UserCreatable *obj, Error **errp)
> > > +{
> > > +    char *name = NULL;
> > > +    Error *local_error = NULL;
> > > +    ThrottleGroup *tg = THROTTLE_GROUP(obj);
> > > +
> > > +    name = object_get_canonical_path_component(OBJECT(obj));
> > > +    if (throttle_group_exists(name)) {
> > > +        error_setg(&local_error, "A throttle group with this name 
> > > already \
> > > +                                  exists.");
> > > +        goto ret;
> > > +    }
> > 
> > QOM should enforce unique id=<ID>.  I don't think this is necessary.
> > 
> > > +
> > > +    qemu_mutex_lock(&throttle_groups_lock);
> > > +    tg->name = name;
> > > +    qemu_mutex_init(&tg->lock);
> > > +    QLIST_INIT(&tg->head);
> > > +    QTAILQ_INSERT_TAIL(&throttle_groups, tg, list);
> > > +    tg->refcount++;
> > > +    qemu_mutex_unlock(&throttle_groups_lock);
> > > +
> 
> Sorry for the multiple replies but I just remembered this.
> 
> This is necessary because throttle groups are created by other interfaces as
> well. Of course block/throttle-groups.c could use only QOM objects
> internally to eliminate the housekeeping.

I suggest all throttle group objects are visible in QOM.  Who are the
non-QOM users?

I have CCed Pradeep who has been working on virtio-9p throttling.

Pradeep: You may be interested in this series, which makes the throttle
group a QOM object (-object throttle-group,id=group0,bps=1235678).  In
other words, groups are becoming first-class objects instead of being
hidden behind the member devices that use them.

Stefan

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