Subject: Re: [kvm-devel] [PATCH 3/3] virtio PCI device
From: Zachary Amsden <zach@vmware.com>
To: Avi Kivity <avi@qumranet.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, kvm-devel@lists.sourceforge.net,
       virtualization@lists.osdl.org, linux-kernel@vger.kernel.org,
       Eric Van Hensbergen <ericvanhensbergen@us.ibm.com>
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Date: Wed, 21 Nov 2007 10:22:57 -0800
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On Wed, 2007-11-21 at 09:13 +0200, Avi Kivity wrote:

> Where the device is implemented is an implementation detail that should 
> be hidden from the guest, isn't that one of the strengths of 
> virtualization?  Two examples: a file-based block device implemented in 
> qemu gives you fancy file formats with encryption and compression, while 
> the same device implemented in the kernel gives you a low-overhead path 
> directly to a zillion-disk SAN volume.  Or a user-level network device 
> capable of running with the slirp stack and no permissions vs. the 
> kernel device running copyless most of the time and using a dma engine 
> for the rest but requiring you to be good friends with the admin.
> 
> The user should expect zero reconfigurations moving a VM from one model 
> to the other.

I think that is pretty insightful, and indeed, is probably the only
reason we would ever consider using a virtio based driver.

But is this really a virtualization problem, and is virtio the right
place to solve it?  Doesn't I/O hotplug with multipathing or NIC teaming
provide the same infrastructure in a way that is useful in more than
just a virtualization context?

Zach

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