linux-kernel - Re: [PATCH V5 4/9] virtio: introduce vring_mapping

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Message-ID: <20250814063927-mutt-send-email-mst@kernel.org>
Date: Thu, 14 Aug 2025 06:42:15 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
	hch@...radead.org
Subject: Re: [PATCH V5 4/9] virtio: introduce vring_mapping_token

On Thu, Aug 14, 2025 at 11:36:22AM +0800, Jason Wang wrote:
> > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > index addbc209275a..37029df94aaf 100644
> > > --- a/include/linux/virtio.h
> > > +++ b/include/linux/virtio.h
> > > @@ -40,6 +40,13 @@ struct virtqueue {
> > >       void *priv;
> > >  };
> > >
> > > +union vring_mapping_token {
> > > +     /* Device that performs DMA */
> > > +     struct device *dma_dev;
> > > +     /* Transport specific token used for doing map */
> > > +     void *opaque;
> >
> > Please just declare whatever structure you want it to be.
> 
> It's an opaque one and so
> 
> 1) the virtio core knows nothing about that because it could be
> transport or device specific
> 2) no assumption of the type and usage, it just receive it from the
> transport and pass it back when doing the mapping
> 
> It should work like page->private etc.
> 
> Does this make sense?
> 
> Thanks

I fully expect most devices simply to use DMA here and no weird
tricks. vduse is the weird one, but I don't see us making it
grow much beyond that.

So I think for now we can just make it vduse_iova_domain *. If we see
it's getting out of hand with too many types, we can think of solutions.

-- 
MST