netdev - Re: [PATCH V3 2/8] Add a new zerocopy device flag

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Message-ID: <20110502195302.GA25619@redhat.com>
Date:	Mon, 2 May 2011 22:53:03 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/8] Add a new zerocopy device flag

On Mon, May 02, 2011 at 11:47:08AM -0700, Shirley Ma wrote:
> On Mon, 2011-05-02 at 13:42 +0300, Michael S. Tsirkin wrote:
> > This comment should specify what exactly is the promise the
> > device makes by setting this flag. Specifically, the
> > condition is that no skb fragments are used
> > after the uinfo callback has been called.
> > 
> > The way it's implemented, it probably means the device
> > should not use any of skb_clone, expand head etc.
> 
> Agree. Or maybe force a copy when device uses skb_clone, expand
> head ...?
> 
> Thanks
> Shirley

Copy from userspace upfront without locking is probably cheaper?

-- 
MST
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