Re: [PATCH V2 3/5] vDPA: introduce vDPA bus

From: Jason Wang <jasowang@redhat.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: mst@redhat.com, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, tiwei.bie@intel.com,
	maxime.coquelin@redhat.com, cunming.liang@intel.com,
	zhihong.wang@intel.com, rob.miller@broadcom.com,
	xiao.w.wang@intel.com, haotian.wang@sifive.com,
	lingshan.zhu@intel.com, eperezma@redhat.com, lulu@redhat.com,
	parav@mellanox.com, kevin.tian@intel.com, stefanha@redhat.com,
	rdunlap@infradead.org, hch@infradead.org, aadam@redhat.com,
	jiri@mellanox.com, shahafs@mellanox.com, hanand@xilinx.com,
	mhabets@solarflare.com
Subject: Re: [PATCH V2 3/5] vDPA: introduce vDPA bus
Date: Thu, 13 Feb 2020 11:34:10 +0800	[thread overview]
Message-ID: <12775659-1589-39e4-e344-b7a2c792b0f3@redhat.com> (raw)
In-Reply-To: <20200212125108.GS4271@mellanox.com>

On 2020/2/12 下午8:51, Jason Gunthorpe wrote:
> On Wed, Feb 12, 2020 at 03:55:31PM +0800, Jason Wang wrote:
>>> The ida_simple_remove should probably be part of the class release
>>> function to make everything work right
>> It looks to me bus instead of class is the correct abstraction here since
>> the devices share a set of programming interface but not the semantics.
> device_release() doesn't call the bus release?

What it did is:

         if (dev->release)
                 dev->release(dev);
         else if (dev->type && dev->type->release)
                 dev->type->release(dev);
         else if (dev->class && dev->class->dev_release)
                 dev->class->dev_release(dev);
         else
                 WARN(1, KERN_ERR "Device '%s' does not have a release() 
function, it is broken and must be fixed. See Documentation/kobject.txt.\n",
                         dev_name(dev));

So it looks not.

>   You have dev, type or
> class to choose from. Type is rarely used and doesn't seem to be used
> by vdpa, so class seems the right choice
>
> Jason

Yes, but my understanding is class and bus are mutually exclusive. So we 
can't add a class to a device which is already attached on a bus.

Thanks