netdev - How net_device feature flag of 'tx-udp

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Message-ID: <CAFAx9ab=Wys2QU+nsh-O_XyOKw9T1ACziphzRW4ARYAwA30xEw@mail.gmail.com>
Date:   Fri, 7 Jun 2019 15:56:48 +0900
From:   양유석 <ileixe@...il.com>
To:     netdev@...r.kernel.org
Subject: How net_device feature flag of 'tx-udp_tnl-segmetnation' is decided?

Hi netdev!

I'm kernel newbie and I'm not sure it's right place to ask though, if
not please let me know the right place. :)

I sent this mail to ask about net_device interface feature called
'tx-udp_tnl-segmentation'. Ethtool does not appear correct status of
offloading, even if the vxlan offloading is enabled. Ethtool show like
below for vxlan interface.

deploy@...ne-pg1-com1000:~$ ethtool --show-offload vxlan100
Features for vxlan100:
tx-udp_tnl-segmentation: off [fixed]

deploy@...ne-pg1-com1000:~$ ethtool --show-offload eth0
Features for eth0:
tx-udp_tnl-csum-segmentation: on

Tcpdumping show offload is correctly applied in vxlan interface, so I
wonder this is bug for vxlan implementation. I found
drivers/net/vxlan.c does not set the feature SKB_GSO_UDP_TUNNEL, just
applying the flag at creation time. Is it bug or something that I
misunderstood?

Thanks in advance!

Best regards

Yang Youseok