linux-kernel - Re: [PATCH 3/3] vDPA/ifcvf: get_config_size should return dev specific config size

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Date:   Thu, 15 Apr 2021 16:16:20 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     mst@...hat.com, lulu@...hat.com, leonro@...dia.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] vDPA/ifcvf: get_config_size should return dev
 specific config size


在 2021/4/15 下午4:12, Stefano Garzarella 写道:
> On Wed, Apr 14, 2021 at 05:18:32PM +0800, Zhu Lingshan wrote:
>> get_config_size() should return the size based on the decected
>> device type.
>>
>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>> ---
>> drivers/vdpa/ifcvf/ifcvf_main.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c 
>> b/drivers/vdpa/ifcvf/ifcvf_main.c
>> index 9b6a38b798fa..b48b9789b69e 100644
>> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
>> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
>> @@ -347,7 +347,16 @@ static u32 ifcvf_vdpa_get_vq_align(struct 
>> vdpa_device *vdpa_dev)
>>
>> static size_t ifcvf_vdpa_get_config_size(struct vdpa_device *vdpa_dev)
>> {
>> -    return sizeof(struct virtio_net_config);
>> +    struct ifcvf_hw *vf = vdpa_to_vf(vdpa_dev);
>> +    size_t size;
>> +
>> +    if (vf->dev_type == VIRTIO_ID_NET)
>> +        size = sizeof(struct virtio_net_config);
>> +
>> +    if (vf->dev_type == VIRTIO_ID_BLOCK)
>> +        size = sizeof(struct virtio_blk_config);
>> +
>> +    return size;
>
> I'm not familiar with the ifcvf details, but can it happen that the 
> device is not block or net?
>
> Should we set `size` to 0 by default to handle this case or are we 
> sure it's one of the two?
>
> Maybe we should add a comment or a warning message in this case, to 
> prevent some analysis tool or compiler from worrying that `size` might 
> be uninitialized.
>
> I was thinking something like this:
>
>     switch(vf->dev_type) {
>     case VIRTIO_ID_NET:
>         size = sizeof(struct virtio_net_config);
>         break;
>     case VIRTIO_ID_BLOCK:
>         size = sizeof(struct virtio_blk_config);
>         break;
>     default:
>         /* or WARN(1, "") if dev_warn() not apply */
>         dev_warn(... , "virtio ID [0x%x] not supported\n")
>         size = 0;
>
>     }
>

Yes, I agree.

Thanks


> Thanks,
> Stefano
>