netdev - Re: [PATCH V6 8/8] virtio: Intel IFC VF driver for VDPA

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Date:   Thu, 19 Mar 2020 16:14:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     mst@...hat.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        maxime.coquelin@...hat.com, cunming.liang@...el.com,
        zhihong.wang@...el.com, rob.miller@...adcom.com,
        xiao.w.wang@...el.com, lingshan.zhu@...el.com, eperezma@...hat.com,
        lulu@...hat.com, parav@...lanox.com, kevin.tian@...el.com,
        stefanha@...hat.com, rdunlap@...radead.org, hch@...radead.org,
        aadam@...hat.com, jiri@...lanox.com, shahafs@...lanox.com,
        hanand@...inx.com, mhabets@...arflare.com, gdawar@...inx.com,
        saugatm@...inx.com, vmireyno@...vell.com,
        Bie Tiwei <tiwei.bie@...el.com>
Subject: Re: [PATCH V6 8/8] virtio: Intel IFC VF driver for VDPA


On 2020/3/18 下午8:22, Jason Gunthorpe wrote:
> On Wed, Mar 18, 2020 at 04:03:27PM +0800, Jason Wang wrote:
>> From: Zhu Lingshan <lingshan.zhu@...el.com>
>> +
>> +static int ifcvf_vdpa_attach(struct ifcvf_adapter *adapter)
>> +{
>> +	int ret;
>> +
>> +	adapter->vdpa_dev  = vdpa_alloc_device(adapter->dev, adapter->dev,
>> +					       &ifc_vdpa_ops);
>> +	if (IS_ERR(adapter->vdpa_dev)) {
>> +		IFCVF_ERR(adapter->dev, "Failed to init ifcvf on vdpa bus");
>> +		put_device(&adapter->vdpa_dev->dev);
>> +		return -ENODEV;
>> +	}
> The point of having an alloc call is so that the drivers
> ifcvf_adaptor memory could be placed in the same struct - eg use
> container_of to flip between them, and have a kref for both memories.
>
> It seem really weird to have an alloc followed immediately by
> register.


I admit the ifcvf_adapter is not correctly ref-counted. What you suggest 
should work. But it looks to me the following is more cleaner since the 
members of ifcvf_adapter are all related to PCI device not vDPA itself.

- keep the current layout of ifcvf_adapter
- merge vdpa_alloc_device() and vdpa_register_device()
- use devres to bind ifcvf_adapter refcnt/lifcycle to the under PCI device

If we go for the container_of method, we probably need

- accept a size of parent parent structure in vdpa_alloc_device() and 
mandate vdpa_device to be the first member of ifcvf_adapter
- we need provide a way to free resources of parent structure when we 
destroy vDPA device

What's your thought?


>> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
>> index c30eb55030be..de64b88ee7e4 100644
>> +++ b/drivers/virtio/virtio_vdpa.c
>> @@ -362,6 +362,7 @@ static int virtio_vdpa_probe(struct vdpa_device *vdpa)
>>   		goto err;
>>   
>>   	vdpa_set_drvdata(vdpa, vd_dev);
>> +	dev_info(vd_dev->vdev.dev.parent, "device attached to VDPA bus\n");
>>   
>>   	return 0;
> This hunk seems out of place
>
> Jason


Right, will fix.

Thanks