Re: [PATCH net 0/5] Implement ndo_gso_check() for vxlan nics

[Jesse Gross <jesse@nicira.com>]

On Thu, Nov 6, 2014 at 8:06 AM, Tom Herbert <therbert@google.com> wrote:
> On Wed, Nov 5, 2014 at 10:16 PM, Sathya Perla <Sathya.Perla@emulex.com> wrote:
>>> -----Original Message-----
>>> From: Tom Herbert [mailto:therbert@google.com]
>>>
>>> On Wed, Nov 5, 2014 at 6:15 PM, David Miller <davem@davemloft.net>
>>> wrote:
>>> > From: Joe Stringer <joestringer@nicira.com>
>>> > Date: Wed, 5 Nov 2014 17:06:46 -0800
>>> >
>>> >> My impression was that the changes are more likely to be
>>> >> hardware-specific (like the i40e changes) rather than software-specific,
>>> >> like changes that might be integrated into the helper.
>>> >
>>> > I think there is more commonality amongst hardware capabilities,
>>> > and this is why I want the helper to play itself out.
>>> >
>>> >> That said, I can rework for one helper. The way I see it would be the
>>> >> same code as these patches, as "vxlan_gso_check(struct sk_buff *)" in
>>> >> drivers/net/vxlan.c which would be called from each driver. Is that what
>>> >> you had in mind?
>>> >
>>> > Yes.
>>>
>>> Note that this code is not VXLAN specific, it will also accept NVGRE
>>> and GRE/UDP with keyid and TEB. I imagine all these cases should be
>>> indistinguishable to the hardware so they probably just work (which
>>> would be cool!). It might be better to name and locate the helper
>>> function to reflect that.
>>
>> Tom, I'm confused as to how the value of (skb_inner_mac_header(skb) - skb_transport_header(skb))
>> would be the same for VxLAN and NVGRE encapsulated packets. Wouldn't this value be 16 for VxLAN
>> and 8 for NVGRE?
>>
> The inner headers are reset in iptunnel_handle_offloads. This is
> called in the xmit encapsulation functions (GRE, fou, VXLAN, etc.)
> before adding in encapsulation headers (skb_push), so the
> mac_inner_header will point to the encapsulation payload, i.e. the
> encapsulated packet. This should not change after being set, although
> inner network and inner transport can. The headers are only set on the
> first encapsulation, so with nested tunnels the inner headers point to
> the innermost encapsulated packet. Since VXLAN and NVGRE have same
> size of encapsulation (8 UDP + 8 header),   skb_inner_mac_header(skb)
> - skb_transport_header(skb) should always be 16.

Tom, NVGRE is not encapsulated in UDP and it is not 16 bytes.

http://tools.ietf.org/html/draft-sridharan-virtualization-nvgre-06