netdev - Re: [PATCH v4 net-next 09/11] net: Add IPv6 flow label to flow

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Date:	Fri, 22 May 2015 13:12:38 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 net-next 09/11] net: Add IPv6 flow label to flow_keys

On Fri, May 22, 2015 at 8:22 AM, Jiri Pirko <jiri@...nulli.us> wrote:
> Fri, May 22, 2015 at 05:14:21PM CEST, tom@...bertland.com wrote:
>>On Fri, May 22, 2015 at 1:14 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>> Fri, May 22, 2015 at 02:11:44AM CEST, tom@...bertland.com wrote:
>>>>In flow_dissector set the flow label in flow_keys for IPv6. This also
>>>>removes the shortcircuiting of flow dissection when a non-zero label
>>>>is present, the flow label can be considered to provide additional
>>>>entropy for a hash.
>>>>
>>>>Signed-off-by: Tom Herbert <tom@...bertland.com>
>>>>---
>>>> include/net/flow_dissector.h |  4 +++-
>>>> net/core/flow_dissector.c    | 37 +++++++++++++------------------------
>>>> 2 files changed, 16 insertions(+), 25 deletions(-)
>>>>
>>>>diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
>>>>index 08480fb..effe607 100644
>>>>--- a/include/net/flow_dissector.h
>>>>+++ b/include/net/flow_dissector.h
>>>>@@ -28,7 +28,8 @@ struct flow_dissector_key_basic {
>>>> };
>>>>
>>>> struct flow_dissector_key_tags {
>>>>-      u32     vlan_id:12;
>>>>+      u32     vlan_id:12,
>>>>+              flow_label:20;
>>>> };
>>>>
>>>> /**
>>>>@@ -111,6 +112,7 @@ enum flow_dissector_key_id {
>>>>       FLOW_DISSECTOR_KEY_ETH_ADDRS, /* struct flow_dissector_key_eth_addrs */
>>>>       FLOW_DISSECTOR_KEY_TIPC_ADDRS, /* struct flow_dissector_key_tipc_addrs */
>>>>       FLOW_DISSECTOR_KEY_VLANID, /* struct flow_dissector_key_flow_tags */
>>>>+      FLOW_DISSECTOR_KEY_FLOW_LABEL, /* struct flow_dissector_key_flow_label */
>>>
>>>
>>> I think it makes sense to pair FLOW_DISSECTOR_KEY_* with
>>> struct flow_dissector_key_*
>>>
>>> How about to have FLOW_DISSECTOR_KEY_TAGS istead of VLANID and FLOW_LABEL?
>>>
>>
>>I thought about that, but it doesn't really save anything to be less
>>explicit as we still need a conditional at each occurrence. If someone
>>is only looking for IPv6 flow label and nothing else they are able to
>>do that.
>
> So have 2 structs then.

We also use this structure in flow_keys and it's convenient to packet
both VLAN and and flow label into single structure in that case. So we
get precisely 24 or 48 bytes in flow_keys from skb_flow_dissector with
the trick os setting keys to same field. The comment for
FLOW_DISSECTOR_KEY_FLOW_LABEL does need to be fixed.
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