Re: [Qemu-devel] [PATCH] VirtIO Support for Memory Regions

[Anthony Liguori]

On 02/24/2010 09:13 AM, Anthony Liguori wrote:
> > to work on that if we can agree on what the underlying device looks
> > like whether it should be VirtIO or just PCI.
> Agreed, you had suggested uio_pci for my PCI driver and I'd be happy
>
> I feel pretty strongly that we shouldn't add shared memory to virtio.  
> I'm pretty sure Christian would too because it eliminates the 
> possibility of implementing a copy-based transport for virtio 
> (virtio-over-ethernet).

Actually, ignore my crazy justification based on virtio-over-ethernet :-)

Certain hypervisors (like Xen and PHYP) have very limited/non-existent 
support for shared memory.  In the case of Xen, there's a very small 
pool that can be used for DMA buffers.  In the case of PHYP, you have 
hardware accelerated copying for all I/O.

Adding shared memory to virtio means that virtio could not be supported 
(or at least, all virtio devices) on these hypervisors.

Regards,

Anthony Liguori