Re: guest / host buffer sharing ...

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Nov 05, 2019 at 11:54:56AM +0100, Gerd Hoffmann wrote:
> The issue of sharing buffers between guests and hosts keeps poping
> up again and again in different contexts.  Most recently here:
> 
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg656685.html
> 
> So, I'm grabbing the recipient list of the virtio-vdec thread and some
> more people I know might be interested in this, hoping to have everyone
> included.
> 
> Reason is:  Meanwhile I'm wondering whenever "just use virtio-gpu
> resources" is really a good answer for all the different use cases
> we have collected over time.  Maybe it is better to have a dedicated
> buffer sharing virtio device?  Here is the rough idea:

My concern is that buffer sharing isn't a "device".  It's a primitive
used in building other devices.  When someone asks for just buffer
sharing it's often because they do not intend to upstream a
specification for their device.

If this buffer sharing device's main purpose is for building proprietary
devices without contributing to VIRTIO, then I don't think it makes
sense for the VIRTIO community to assist in its development.

VIRTIO recently gained a shared memory resource concept for access to
host memory.  It is being used in virtio-pmem and virtio-fs (and
virtio-gpu?).  If another flavor of shared memory is required it can be
added to the spec and new VIRTIO device types can use it.  But it's not
clear why this should be its own device.

My question would be "what is the actual problem you are trying to
solve?".

Stefan

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