netdev - Re: [PATCH net-next repost] openvswitch: allow output of MPLS packets on tunnel vports

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Message-ID: <CAEh+42h-w5Xm2i3H8auNCO4U3yYBadU7GsWFe7dwiKNcBq1dGg@mail.gmail.com>
Date:	Tue, 15 Mar 2016 10:05:25 -0700
From:	Jesse Gross <jesse@...nel.org>
To:	Simon Horman <simon.horman@...ronome.com>
Cc:	Pravin Shelar <pshelar@....org>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	ovs dev <dev@...nvswitch.org>
Subject: Re: [PATCH net-next repost] openvswitch: allow output of MPLS packets
 on tunnel vports

On Mon, Mar 14, 2016 at 8:00 PM, Simon Horman
<simon.horman@...ronome.com> wrote:
> Currently output of MPLS packets on tunnel vports is not allowed by Open
> vSwitch. This is because historically encapsulation was done in such a way
> that the inner_protocol field of the skb needed to hold the inner protocol
> for both MPLS and tunnel encapsulation in order for GSO segmentation to be
> performed correctly.
>
> Since b2acd1dc3949 ("openvswitch: Use regular GRE net_device instead of
> vport") Open vSwitch makes use of lwt to output to tunnel netdevs which
> perform encapsulation. As no drivers expose support for MPLS offloads this
> means that GSO packets are segmented in software by validate_xmit_skb(),
> which is called from __dev_queue_xmit(), before tunnel encapsulation occurs.
> This means that the inner protocol of MPLS is no longer needed by the time
> encapsulation occurs and the contention on the inner_protocol field of the
> skb no longer occurs.
>
> Thus it is now safe to output MPLS to tunnel vports.
>
> Signed-off-by: Simon Horman <simon.horman@...ronome.com>

Reviewed-by: Jesse Gross <jesse@...nel.org>