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Date: Mon, 19 Oct 2015 09:43:16 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: "Xie, Huawei" <huawei.xie@intel.com>
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Cc: "dev@dpdk.org" <dev@dpdk.org>,
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Subject: Re: [dpdk-dev] [PATCH 4/5] virtio: use any layout on transmit
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On Mon, 19 Oct 2015 16:28:30 +0000
"Xie, Huawei" <huawei.xie@intel.com> wrote:

> On 10/19/2015 1:16 PM, Stephen Hemminger wrote:
> > Virtio supports a feature that allows sender to put transmit
> > header prepended to data.  It requires that the mbuf be writeable, correct
> > alignment, and the feature has been negotiatied.  If all this works out,
> > then it will be the optimum way to transmit a single segment packet.  
> "When using legacy interfaces, transitional drivers which have not
> negotiated VIRTIO_F_ANY_LAYOUT
> MUST use a single descriptor for the struct virtio_net_hdr on both
> transmit and receive, with the
> network data in the following descriptors."

The code checks for the any layout feature, what is the problem?