netdev - Re: [PATCH V13 6/6] docs: sample driver to demonstrate how to implement virtio-mdev framework

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Date:   Mon, 18 Nov 2019 16:45:10 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
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Subject: Re: [PATCH V13 6/6] docs: sample driver to demonstrate how to
 implement virtio-mdev framework

On Mon, 18 Nov 2019 18:59:23 +0800
Jason Wang <jasowang@...hat.com> wrote:

[Note: I have not looked into the reworked architecture of this *at all*
so far; just something that I noted...]

> This sample driver creates mdev device that simulate virtio net device
> over virtio mdev transport. The device is implemented through vringh
> and workqueue. A device specific dma ops is to make sure HVA is used
> directly as the IOVA. This should be sufficient for kernel virtio
> driver to work.
> 
> Only 'virtio' type is supported right now. I plan to add 'vhost' type
> on top which requires some virtual IOMMU implemented in this sample
> driver.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  MAINTAINERS                        |   1 +
>  samples/Kconfig                    |  10 +
>  samples/vfio-mdev/Makefile         |   1 +
>  samples/vfio-mdev/mvnet_loopback.c | 690 +++++++++++++++++++++++++++++
>  4 files changed, 702 insertions(+)
>  create mode 100644 samples/vfio-mdev/mvnet_loopback.c
> 

> +static struct mvnet_dev {
> +	struct class	*vd_class;
> +	struct idr	vd_idr;
> +	struct device	dev;
> +} mvnet_dev;

This structure embeds a struct device (a reference-counted structure),
yet it is a static variable. This is giving a bad example to potential
implementers; just allocate it dynamically.

> +static void mvnet_device_release(struct device *dev)
> +{
> +	dev_dbg(dev, "mvnet: released\n");

And that also means you need a proper release function here, of
course.

> +}