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

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Date:   Thu, 15 Apr 2021 10:12:36 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     jasowang@...hat.com, 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

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;

	}

Thanks,
Stefano