Subject: Re: [PATCH rdma-next v1 05/11] RDMA/counter: Add optional counter support

From: Jason Gunthorpe <[email-masked]>
Date: Tue, 28 Sep 2021 08:51:35 -0300

On Tue, Sep 28, 2021 at 05:03:24PM +0800, Mark Zhang wrote:
> On 9/28/2021 1:03 AM, Jason Gunthorpe wrote:
> > On Wed, Sep 15, 2021 at 02:07:24AM +0300, Leon Romanovsky wrote:
> > > +int rdma_counter_modify(struct ib_device *dev, u32 port, int index, bool enable)
> > > +{
> > > +	struct rdma_hw_stats *stats;
> > > +	int ret;
> > > +
> > > +	if (!dev->ops.modify_hw_stat)
> > > +		return -EOPNOTSUPP;
> > > +
> > > +	stats = ib_get_hw_stats_port(dev, port);
> > > +	if (!stats)
> > > +		return -EINVAL;
> > > +
> > > +	mutex_lock(&stats->lock);
> > > +	ret = dev->ops.modify_hw_stat(dev, port, index, enable);
> > > +	if (!ret)
> > > +		enable ? clear_bit(index, stats->is_disabled) :
> > > +			set_bit(index, stats->is_disabled);
> > 
> > This is not a kernel coding style write out the if, use success
> > oriented flow
> > 
> > Also, shouldn't this logic protect the driver from being called on
> > non-optional counters?
> 
> We leave it to driver, driver would return failure if modify is not
> supported. Is it good?

I think the core code should do it

> > >   	for (i = 0; i < data->stats->num_counters; i++) {
> > > -		attr = &data->attrs[i];
> > > +		if (data->stats->descs[i].flags & IB_STAT_FLAG_OPTIONAL)
> > > +			continue;
> > > +		attr = &data->attrs[pos];
> > >   		sysfs_attr_init(&attr->attr.attr);
> > >   		attr->attr.attr.name = data->stats->descs[i].name;
> > >   		attr->attr.attr.mode = 0444;
> > >   		attr->attr.show = hw_stat_device_show;
> > >   		attr->show = show_hw_stats;
> > > -		data->group.attrs[i] = &attr->attr.attr;
> > > +		data->group.attrs[pos] = &attr->attr.attr;
> > > +		pos++;
> > >   	}
> > 
> > This isn't OK, the hw_stat_device_show() computes the stat index like
> > this:
> > 
> > 	return stat_attr->show(ibdev, ibdev->hw_stats_data->stats,
> > 			       stat_attr - ibdev->hw_stats_data->attrs, 0, buf);
> > 
> > Which assumes the stats are packed contiguously. This only works
> > because mlx5 is always putting the optional stats at the end.
> 
> Yes you are right, thanks. Maybe we can add an "index" field in struct
> hw_stats_device/port_attribute, then set it in setup and use it in show.

You could just add a WARN_ON check that optional stats are at the end
I suppose

Jason