linux-kernel - Re: [kvm-devel] [PATCH 3/3] virtio PCI device

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Message-Id: <1195669377.6352.247.camel@bodhitayantram.eng.vmware.com>
Date:	Wed, 21 Nov 2007 10:22:57 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Anthony Liguori <aliguori@...ibm.com>,
	kvm-devel@...ts.sourceforge.net, virtualization@...ts.osdl.org,
	linux-kernel@...r.kernel.org,
	Eric Van Hensbergen <ericvanhensbergen@...ibm.com>
Subject: Re: [kvm-devel] [PATCH 3/3] virtio PCI device

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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