Re: [PATCH v5] Drivers: hv: vmbus: Expose monitor data only when monitor pages are used

From: Kimberly Brown <kimbrownkd@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Michael Kelley <mikelley@microsoft.com>,
	Long Li <longli@microsoft.com>,
	Sasha Levin <Alexander.Levin@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Dexuan Cui <decui@microsoft.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5] Drivers: hv: vmbus: Expose monitor data only when monitor pages are used
Date: Mon, 11 Mar 2019 20:04:50 -0400	[thread overview]
Message-ID: <20190312000449.GA2741@ubu-Virtual-Machine> (raw)
In-Reply-To: <20190309072135.GG3882@kroah.com>

On Sat, Mar 09, 2019 at 08:21:35AM +0100, Greg KH wrote:
> On Fri, Mar 08, 2019 at 05:46:11PM -0500, Kimberly Brown wrote:
> >  static struct kobj_type vmbus_chan_ktype = {
> >  	.sysfs_ops = &vmbus_chan_sysfs_ops,
> >  	.release = vmbus_chan_release,
> > -	.default_attrs = vmbus_chan_attrs,
> 
> As discussed on IRC, a kobj_type needs to get an attribute group one of
> these days, not just a attribute list :)
> 
> So thanks for persisting with this, sorry for the earlier review
> comments, you were totally right about this, nice work.
> 
> Minor review comments below:
> 
> >  };
> >  
> >  /*
> > @@ -1571,11 +1624,34 @@ int vmbus_add_channel_kobj(struct hv_device *dev, struct vmbus_channel *channel)
> >  	if (ret)
> >  		return ret;
> >  
> > +	ret = sysfs_create_group(kobj, &vmbus_chan_group);
> > +	channel->sysfs_group_ready = !ret;
> 
> Why do you need this flag?
> 

I added this flag to prevent sysfs_remove_group() from being called if
sysfs_create_group() or the earlier call to kobject_init_and_add()
failed. However, it looks like that would just lead to WARN() being
called, which seems appropriate. I'll remove this flag.

> > +
> > +	if (ret) {
> > +		/*
> > +		 * If an error is returned to the calling functions, those
> > +		 * functions will call kobject_put() on the channel kobject,
> > +		 * which will cleanup the empty channel directory created by
> > +		 * kobject_init_and_add().
> 
> Why is this comment needed?
> 

Another reviewer asked why the empty directory created by
kobject_init_and_add() isn't removed here when sysfs_create_group()
fails. We decided that a comment would help clear up any future
confusion.

> > +		 */
> > +		pr_err("Unable to set up channel sysfs files\n");
> 
> dev_err() to show who had the problem with the files?
>

Yes, good point. I'll change this.

> > +		return ret;
> > +	}
> > +
> >  	kobject_uevent(kobj, KOBJ_ADD);
> >  
> >  	return 0;
> >  }
> >  
> > +/*
> > + * vmbus_remove_channel_attr_group - remove the channel's attribute group
> > + */
> > +void vmbus_remove_channel_attr_group(struct vmbus_channel *channel)
> > +{
> > +	if (channel->sysfs_group_ready)
> > +		sysfs_remove_group(&channel->kobj, &vmbus_chan_group);
> 
> You should be able to just always remove these, no need for a flag to
> say you have created them or not, right?
> 
> thanks,
> 
> greg k-h