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

Eelco Chaudron echaudro at redhat.com
Thu Jun 3 08:01:32 UTC 2021



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.

>> +    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.

>> +
>>  # 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">



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