netdev - Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work

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Date:	Mon, 09 Apr 2007 12:50:18 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Ingo Molnar <mingo@...e.hu>, kvm-devel@...ts.sourceforge.net,
	netdev <netdev@...r.kernel.org>
Subject: Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work

On Sun, 2007-04-08 at 08:36 +0300, Avi Kivity wrote:
> Rusty Russell wrote:
> > Hi Avi,
> >
> > 	I don't think you've thought about this very hard.  The receive copy is
> > completely independent with whether the packet is going to the guest via
> > a kernel driver or via userspace, so not relevant.
> >   
> 
> A packet received in the kernel cannot be made available to userspace in 
> a safe manner without a copy, as it will not be aligned with page 
> boundaries, so userspace cannot examine the packet until after one copy 
> has occured.

Hi Avi!

	I'm a little puzzled by your response.  Hmm...

	lguest's userspace network frontend does exactly as many copies as
Ingo's in-host-kernel code.  One from the Guest, one to the Guest.

Does that clarify?
Rusty.

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