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Date: Wed, 14 Apr 2010 22:39:49 +0200 From: Arnd Bergmann <arnd@...db.de> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: xiaohui.xin@...el.com, netdev@...r.kernel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...e.hu, davem@...emloft.net, jdike@...ux.intel.com Subject: Re: [RFC][PATCH v3 1/3] A device for zero-copy based on KVM virtio-net. On Wednesday 14 April 2010 22:31:42 Michael S. Tsirkin wrote: > On Wed, Apr 14, 2010 at 06:35:57PM +0200, Arnd Bergmann wrote: > > On Wednesday 14 April 2010, Michael S. Tsirkin wrote: > > > > > > > > > > qemu needs the ability to inject raw packets into device > > > > > from userspace, bypassing vhost/virtio (for live migration). > > > > > > > > Ok, but since there is only a write callback and no read, it won't > > > > actually be able to do this with the current code, right? > > > > > > I think it'll work as is, with vhost qemu only ever writes, > > > never reads from device. We'll also never need GSO etc > > > which is a large part of what tap does (and macvtap will > > > have to do). > > > > Ah, I see. I didn't realize that qemu needs to write to the > > device even if vhost is used. But for the case of migration to > > another machine without vhost, wouldn't qemu also need to read? > > Not that I know. Why? Well, if the guest not only wants to send data but also receive frames coming from other machines, they need to get from the kernel into qemu, and the only way I can see for doing that is to read from this device if there is no vhost support around on the new machine. Maybe we're talking about different things here. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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