linux-kernel - Re: [PATCH] VFIO/VMBUS: Add VFIO VMBUS driver support

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Date:   Mon, 11 Nov 2019 09:29:48 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     lantianyu1986@...il.com, alex.williamson@...hat.com,
        cohuck@...hat.com, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>, sashal@...nel.org,
        mchehab+samsung@...nel.org, davem@...emloft.net, robh@...nel.org,
        Jonathan.Cameron@...wei.com, paulmck@...ux.ibm.com,
        Michael Kelley <mikelley@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, vkuznets <vkuznets@...hat.com>
Subject: Re: [PATCH] VFIO/VMBUS: Add VFIO VMBUS driver support

On Mon, 11 Nov 2019 18:23:22 +0100
Greg KH <gregkh@...uxfoundation.org> wrote:

> On Mon, Nov 11, 2019 at 08:47:12AM -0800, Stephen Hemminger wrote:
> > On Mon, 11 Nov 2019 01:49:20 -0800
> > "Greg KH" <gregkh@...uxfoundation.org> wrote:
> >   
> > > > +	ret = sysfs_create_bin_file(&channel->kobj,    
> > > &ring_buffer_bin_attr);  
> > > > +	if (ret)
> > > > +		dev_notice(&dev->device,
> > > > +			   "sysfs create ring bin file failed; %d\n",    
> > > ret);  
> > > > +    
> > > 
> > > Again, don't create sysfs files on your own, the bus code should be
> > > doing this for you automatically and in a way that is race-free.
> > > 
> > > thanks,
> > > 
> > > greg k-h  
> > 
> > The sysfs file is only created if the VFIO/UIO driveris used.  
> 
> That's even worse.  Again, sysfs files should be automatically created
> by the driver core when the device is created.  To randomly add/remove
> random files after that happens means userspace is never notified of
> that and that's not good.
> 
> We've been working for a while to fix up these types of races, don't
> purposfully add new ones for no good reason please :)
> 
> thanks,
> 
> greg k-h

The handler for this sysfs file is in the vfio (and uio) driver.
How would this work if bus handled it?