netdev - Re: [PATCH net-next RFC WIP] Patch for XDP support for virtio

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Message-Id: <20161026.125245.1630138589657247338.davem@davemloft.net>
Date:   Wed, 26 Oct 2016 12:52:45 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     mst@...hat.com
Cc:     brouer@...hat.com, shrijeet@...il.com, tom@...bertland.com,
        netdev@...r.kernel.org, shm@...ulusnetworks.com,
        roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com
Subject: Re: [PATCH net-next RFC WIP] Patch for XDP support for virtio_net

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Wed, 26 Oct 2016 19:36:45 +0300

> On Wed, Oct 26, 2016 at 03:52:02PM +0200, Jesper Dangaard Brouer wrote:
>> On Sat, 22 Oct 2016 04:07:23 +0000
>> Shrijeet Mukherjee <shrijeet@...il.com> wrote:
>> 
>> > This patch adds support for xdp ndo and also inserts the xdp program
>> > call into the merged RX buffers and big buffers paths
>> 
>> I really appreciate you are doing this for virtio_net.
>> 
>> My first question is: Is the (packet) page data writable?
>> (MST might be able to answer?)
>> 
>> As this is currently an XDP requirement[1].  
> 
> I'm not sure I understand what does writable mean.
> Could you explain a bit more pls?
> We do copy data into skb ATM but I plan to change that.

The packet data area must be writable, and the page it lives in must
not be shared with any other entity in the system.

This is because the eBPF program that executes via XDP must be able
to modify and read arbitrary parts of the packet area.