netdev - Re: BUG:af_packet fails to TX TSO frames

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Message-ID: <CAF=yD-+q_h4SE0E9RjE59i2FDYZQ_wV+L6RQjE9B_fszen-y0A@mail.gmail.com>
Date:   Thu, 12 Oct 2017 09:39:43 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Anton Ivanov <anton.ivanov@...-begemot.co.uk>
Cc:     Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: BUG:af_packet fails to TX TSO frames

> If I produce a real vnet frame out of a live kernel frame using
> virtio_net_hdr_from_skb() and try to send it it fails on the check in
> af_packet, while succeeding for tap. If I remove the af_packet check the
> frame is accepted by the hardware too.
>
> If I produce it a synthetic frame + vnet header using the test program - it
> works. Go figure.

Besides looking at the raw frame bytes, also compare the setup
of virtio_net_header, as well as the tcp checksum field. The stack
expects the pseudo header to have already been calculated.

> I am going to continue digging into it.
>
> At the very least I now have a positive test case which uses the same
> semantics as my code so I have something to compare to.

Glad to hear that the test is helpful. I wrote it because I
have run into these exact same issues in the past.