[ovs-dev] [PATCH v4] conntrack: document all-zero IP SNAT behavior and add a test case

Aaron Conole aconole at redhat.com
Thu Jun 3 12:38:56 UTC 2021


Eelco Chaudron <echaudro at redhat.com> writes:

> On 2 Jun 2021, at 18:21, Aaron Conole wrote:
>
>> Eelco Chaudron <echaudro at redhat.com> writes:
>>
>>> Currently, conntrack in the kernel has an undocumented feature referred
>>> to as all-zero IP address SNAT. Basically, when a source port
>>> collision is detected during the commit, the source port will be
>>> translated to an ephemeral port. If there is no collision, no SNAT is
>>> performed.
>>>
>>> This patchset documents this behavior and adds a self-test to verify
>>> it's not changing. In addition, a datapath feature flag is added for
>>> the all-zero IP SNAT case. This will help applications on top of OVS,
>>> like OVN, to determine this feature can be used.
>>>
>>> Signed-off-by: Eelco Chaudron <echaudro at redhat.com>
>>> ---
>>> v4: Added datapath support flag for all-zero SNAT.
>>> v3: Renamed NULL SNAT to all-zero IP SNAT.
>>> v2: Fixed NULL SNAT to only work in the -rpl state to be inline with
>>>     OpenShift-SDN's behavior.
>>>
>>>  lib/ct-dpif.c                    |    8 +++++++
>>>  lib/ct-dpif.h                    |    6 +++++
>>>  lib/dpif-netdev.c                |    1 +
>>>  lib/dpif-netlink.c               |   11 +++++++++
>>>  lib/dpif-provider.h              |    5 ++++
>>>  lib/ovs-actions.xml              |   10 ++++++++
>>>  ofproto/ofproto-dpif.c           |   22 +++++++++++++++++-
>>>  ofproto/ofproto-dpif.h           |    5 +++-
>>>  tests/system-kmod-macros.at      |    7 ++++++
>>>  tests/system-traffic.at          |   46 ++++++++++++++++++++++++++++++++++++++
>>>  tests/system-userspace-macros.at |   10 ++++++++
>>>  vswitchd/vswitch.xml             |    9 +++++++
>>>  12 files changed, 138 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/ct-dpif.c b/lib/ct-dpif.c
>>> index 6a5ba052d..cfc2315e3 100644
>>> --- a/lib/ct-dpif.c
>>> +++ b/lib/ct-dpif.c
>>> @@ -889,3 +889,11 @@ ct_dpif_get_timeout_policy_name(struct dpif *dpif, uint32_t tp_id,
>>>                  dpif, tp_id, dl_type, nw_proto, tp_name, is_generic)
>>>              : EOPNOTSUPP);
>>>  }
>>> +
>>> +int
>>> +ct_dpif_get_features(struct dpif *dpif, enum ct_features *features)
>>> +{
>>
>> NIT-mode:
>>
>> Are these features or capabilities?  I ask because we may want to add
>> support for things like tcp loose mode, etc, and not sure if there would
>> need to be a corresponding set function (to enable / disable), and how
>> that should look.  I'm okay with keeping it as-is for here and adding
>> the corresponding set function later, but it would seem strange to try
>> and "set" support for all-zero snat, etc.
>
> Guess the line between feature and capabilities is rather thin... The
> code for checking the datapath support, check_support(), is calling
> all of this features, rather than capabilities.
>
> I guess ct_zero_snat is a none configurable feature ;) But more
> seriously, I could go ahead and change the naming from feature to
> capability. As most of the configurable "features" have their own
> callback.

I guess it doesn't matter too much, but I worry about whether we start
trying to enable.  Maybe we just make it unsupportable?  I'm just
concerned that when we add things like tcp_loose or try to make
tcp_liberal as a configurable in the kernel DP, there could be some
confusion.  Maybe it isn't too important.  Okay, we can cross those
bridges when we get there.

>>> +    return (dpif->dpif_class->ct_get_features
>>> +            ? dpif->dpif_class->ct_get_features(dpif, features)
>>> +            : EOPNOTSUPP);
>>> +}
>
> <SNIP>
>
>>> diff --git a/tests/system-userspace-macros.at b/tests/system-userspace-macros.at
>>> index 34f82cee3..9f0d38dfb 100644
>>> --- a/tests/system-userspace-macros.at
>>> +++ b/tests/system-userspace-macros.at
>>> @@ -96,6 +96,16 @@ m4_define([CHECK_CONNTRACK_FRAG_OVERLAP])
>>>  #
>>>  m4_define([CHECK_CONNTRACK_NAT])
>>>
>>> +# CHECK_CONNTRACK_ZEROIP_SNAT()
>>> +#
>>> +# Perform requirements checks for running conntrack all-zero IP SNAT tests.
>>> +# The userspace datapath does not support all-zero IP SNAT.
>>> +#
>>> +m4_define([CHECK_CONNTRACK_ZEROIP_SNAT],
>>> +[
>>> +    AT_SKIP_IF([:])
>>> +])
>>
>> I didn't check too close, but maybe it's possible to make this check the
>> capabilities bits and then it could be extended to everywhere.
>
> I was thinking about using "ovs-appctl dpif/show-dp-features" after I
> added the features check. However none of the other test cases do
> this, so I thought there might be a reason? It might be that I need to
> configure/setup OVS to run the test command, and not sure if there is
> a nice clean way to shut down if the feature is not supported.

Okay.  Maybe it's not possible in the test framework.

>>> +
>>>  # CHECK_CONNTRACK_TIMEOUT()
>>>  #
>>>  # Perform requirements checks for running conntrack customized timeout tests.
>>> diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
>>> index 4597a215d..d8ea287d5 100644
>>> --- a/vswitchd/vswitch.xml
>>> +++ b/vswitchd/vswitch.xml
>>> @@ -6126,6 +6126,15 @@ ovs-vsctl add-port br0 p0 -- set Interface p0 type=patch options:peer=p1 \
>>>          True if the datapath supports OVS_ACTION_ATTR_DROP.  If false,
>>>          explicit drop action will not be sent to the datapath.
>>>        </column>
>>> +      <column name="capabilities" key="ct_zero_snat"
>>> +              type='{"type": "boolean"}'>
>>> +        True if the datapath supports all-zero SNAT. This is a special case
>>> +        if the <code>src</code> IP address is configured as all 0's, i.e.,
>>> +        <code>nat(src=0.0.0.0)</code>. In this case, when a source port
>>> +        collision is detected during the commit, the source port will be
>>> +        translated to an ephemeral port. If there is no collision, no SNAT
>>> +        is performed.
>>> +      </column>
>>>      </group>
>>>
>>>      <group title="Common Columns">


Acked-by: Aaron Conole <aconole at redhat.com>



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