netdev - Re: [PATCH net] net: Allow flow dissector to handle non 4-byte aligned headers

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Date:	Mon, 1 Feb 2016 15:32:41 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Tom Herbert <tom@...bertland.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Cc:	sowmini.varadhan@...cle.com, kernel-team@...com
Subject: Re: [PATCH net] net: Allow flow dissector to handle non 4-byte
 aligned headers

Hello.

On 2/1/2016 12:37 AM, Tom Herbert wrote:

> Call get_unaligned_be32 when we access 32-bit fields in
> __skb_flow_dissect. At the beginning check for unlikely case of
> 1-byte aligned packet.
>
> Note that flow_dissector may be asked to parse packet unaligned
> fields in two instances:
>
> 1) Packet from a driver which is aligned to Ethernet header
>     (2-byte alignment)
> 2) Parsing inner headers of a received GRE-TEB packet
>
> Testing: Ran super_netperf tests did not see a regression. This was on
> x86 which does not have problems with unaligned data.
>
> Signed-off-by: Tom Herbert <tom@...bertland.com>
> ---
>   net/core/flow_dissector.c | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index d79699c..1c64a1a 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
[...]
> @@ -116,6 +116,10 @@ EXPORT_SYMBOL(__skb_flow_get_ports);
>    * by flow_dissector from either the skbuff or a raw buffer specified by the
>    * rest parameters.
>    *
> + * This function does not assume 4-byte alignment, but it does assume 2-byte
> + * alignment (false is returned for 1-byte alignment). get_unaligned_be32
> + * is called to get thirty-two values out of the packet.

    32-bit, maybe?

[...]

MBR, Sergei