[ovs-dev] [PATCH v8 5/5] datapath: add layer 3 support to ovs_packet_cmd_execute()

[Jesse Gross]

On Wed, Nov 19, 2014 at 12:51 PM, Jarno Rajahalme <jrajahalme at nicira.com> wrote:
>
> On Nov 17, 2014, at 2:33 PM, Jesse Gross <jesse at nicira.com> wrote:
>
>> On Mon, Nov 17, 2014 at 1:50 PM, Lori Jakab <lojakab at cisco.com> wrote:
>>> On 11/17/14 8:03 PM, Jesse Gross wrote:
>>>> On Mon, Nov 17, 2014 at 9:24 AM, Lorand Jakab <lojakab at cisco.com> wrote:
>>>>> diff --git a/datapath/flow_netlink.c b/datapath/flow_netlink.c
>>>>> index 54510c8..8ca3469 100644
>>>>> --- a/datapath/flow_netlink.c
>>>>> +++ b/datapath/flow_netlink.c
>>>>> @@ -692,6 +692,18 @@ static int metadata_from_nlattrs(struct
>>>>> sw_flow_match *match,  u64 *attrs,
>>>>>                 else
>>>>>                         SW_FLOW_KEY_PUT(match, phy.is_layer3, true,
>>>>> is_mask);
>>>>>         }
>>>>> +       /* Layer 3 packets from user space have the EtherType as metadata
>>>>> */
>>>>> +       if (*attrs & (1ULL << OVS_KEY_ATTR_ETHERTYPE)) {
>>>>
>>>> Is this correct? I thought that EtherType wasn't serialized in this
>>>> case - in other places we extract this from the IP/IPv6 attribute
>>>> directly.
>>>
>>>
>>> For "ovs_flow" Netlink messages we can do that, but not for "ovs_packet"
>>> messages, which only have packet metadata, not the full flow key.  Packet
>>> metadata didn't include EtherType until now, but I unless we use the nibble
>>> from the IP version, we need to add it for layer 3 packets only.
>>
>> Hmm, I see. I think that diverging the Netlink encoding for flow
>> installation vs. metadata is probably not a good idea over the long
>> term. If I remember correctly, I believe the reason for only encoding
>> part of the flow key for metadata was to reduce serialization cost.
>> Jarno is thinking about combining the packet execution with flow
>> installation, which would might make this a moot point. If that's the
>> case, then we can probably solve this issue by just using the full
>> flow key.
>
> I have a patch that adds an optional packet to the flow installation command. However, we need to keep the existing packet execution command for backwards compatibility. Also, there are cases (like exceeded flow limit), where we will not add new flows, but just execute the miss packets.  This means that this problem needs to be solved independently of packet execution.

The source of the problem is that we send part of the flow key instead
of the whole thing, which I believe was only done as an optimization.
If this becomes a rare case rather than the common one, I think we can
just remove the optimization and things will continue to work in all
cases.