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Subject: Re: [PATCH v2 net 2/2] selftests: net: tun: add test for VLAN-tagged GSO without NEEDS_CSUM

Eric Dumazet wrote:

Add a selftest in tun.c verifying that a VLAN-tagged (802.1Q) TCPv4 GSO
packet without VIRTIO_NET_HDR_F_NEEDS_CSUM (both flags = 0 and
flags = VIRTIO_NET_HDR_F_DATA_VALID) is accepted when written to a TAP
device (/dev/net/tun with IFF_TAP | IFF_NO_PI | IFF_VNET_HDR).

Thanks. We must not regress users.

Even those that do dubious things..

What is the use case for TSO without checksum offload? Do we know of real
users?

It would not work whenever segmentation is actually needed. So maybe for
on-host VM-to-VM communication? But that won't segment with properly
configured checksum offload either.