netdev - ethtool features: tx-udp_tnl-csum-segmentation and tx-udp

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Date:   Thu, 29 Apr 2021 12:16:55 +0300
From:   Aya Levin <ayal@...dia.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...dia.com>
CC:     Tariq Toukan <tariqt@...dia.com>, Moshe Shemesh <moshe@...dia.com>,
        "Maria Pasechnik" <mariap@...dia.com>
Subject: ethtool features: tx-udp_tnl-csum-segmentation and
 tx-udp_tnl-segmentation

Hi,

I see a strange behavior when toggling feature flags:
(1) tx-udp_tnl-csum-segmentation
(2) tx-udp_tnl-segmentation

I had a guess that tx-udp_tnl-segmentation is responsible for 
segmentation of inner packets (SKB encapsulation + GSO) while 
tx-udp_tnl-csum-segmentation is responsible for checksum of the inner 
packet (SKB encapsulation  + ip_summed == CHECKSUM_PARTIAL). But testing 
proved me wrong.
What I see is that tx-udp_tnl-csum-segmentation controls TSO on inner, 
while tx-udp_tnl-segmentation has no effect - none of them controls the 
inner csum (ip_summed == CHECKSUM_PARTIAL always).

I looked for answers in documentation 
(Documentation/networking/vxlan.rst), with no luck.

Is the above behavior expected?
What is the role of each feature flag?
More specifically: Why are there 2? What is the difference between them?

Regards,
Aya