Re: [PATCH v6 6/6] hmp: add virtio commands

[Jonah Palmer]

On 7/22/21 5:18 AM, Jason Wang wrote:
> 在 2021/7/21 下午5:11, Jonah Palmer 写道:
> > On 7/13/21 10:40 PM, Jason Wang wrote:
> > > 在 2021/7/12 下午6:35, Jonah Palmer 写道:
> > > > +void hmp_virtio_queue_status(Monitor *mon, const QDict *qdict)
> > > > +{
> > > > +    Error *err = NULL;
> > > > +    const char *path = qdict_get_try_str(qdict, "path");
> > > > +    int queue = qdict_get_int(qdict, "queue");
> > > > +    VirtQueueStatus *s = qmp_x_debug_virtio_queue_status(path, 
> > > > queue, &err);
> > > > +
> > > > +    if (err != NULL) {
> > > > +        hmp_handle_error(mon, err);
> > > > +        return;
> > > > +    }
> > > > +
> > > > +    monitor_printf(mon, "%s:\n", path);
> > > > +    monitor_printf(mon, "  device_type:          %s\n",
> > > > +                   VirtioType_str(s->device_type));
> > > > +    monitor_printf(mon, "  index:                %d\n", 
> > > > s->queue_index);
> > > > +    monitor_printf(mon, "  inuse:                %d\n", s->inuse);
> > > > +    monitor_printf(mon, "  last_avail_idx:       %d (%"PRId64" %% 
> > > > %"PRId64")\n",
> > > > +                   s->last_avail_idx, s->last_avail_idx % 
> > > > s->vring_num,
> > > > +                   s->vring_num);
> > > > +    monitor_printf(mon, "  shadow_avail_idx:     %d (%"PRId64" %% 
> > > > %"PRId64")\n",
> > > > +                   s->shadow_avail_idx, s->shadow_avail_idx % 
> > > > s->vring_num,
> > > > +                   s->vring_num);
> > > > +    monitor_printf(mon, "  used_idx:             %d (%"PRId64" %% 
> > > > %"PRId64")\n",
> > > > +                   s->used_idx, s->used_idx % s->vring_num, 
> > > > s->vring_num);
> > >
> > >
> > > The modular information is not the case of packed ring where the 
> > > queue size does not have to be a power of 2.
> > Doesn't modulo work for any integer, regardless if it's a power of 2 
> > or not? Could you clarify this for me?
>
>
> For packed ring, the index doesn't increase freely, it's always small 
> than the virtqueue size.
>
> So showing the modulo arithmetic seems useless since the device or 
> driver doesn't use modulo for calculating the real offset.
>
> Thanks

I see, got it. Thank you for the explanation.

I should be able to easily determine a packed or split ring via. 
virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED).


Jonah

> > Thank you,