Re: BUG:af_packet fails to TX TSO frames

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Network Development <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>
Subject: Re: BUG:af_packet fails to TX TSO frames
Date: Thu, 12 Oct 2017 12:30:44 -0400	[thread overview]
Message-ID: <CAF=yD-+W2tyXqCS_ueZgu11BB8ON5hdKGOZQOWtfr+HfvqW=Sg@mail.gmail.com> (raw)
In-Reply-To: <e301fbfd-a283-caa1-5915-8be15677ed74@cambridgegreys.com>

On Thu, Oct 12, 2017 at 11:44 AM, Anton Ivanov
<anton.ivanov@cambridgegreys.com> wrote:
> Found it.
>
> Two bugs canceling each other.
> The bind sequence in:  psock_txring_vnet.c is wrong.
>
> It does the following addr.sll_protocol =    htons(ETH_P_IP);
> before calling bind.
>
> If you set addr.sll_protocol to ETH_P_ALL where it should have been in the
> first place the test program blows up with -ENOBUFS

There is no such requirement that the socket should bind to ETH_P_ALL.

> I think what is happening is that this value is taken into account when
> looking at "what should I use to segment it with" in skb_mac_gso_segment
> which is invoked at the end of the verification chain which starts in
> packet_direct_xmit in af_packet.c

packet_snd sets skb->protocol based on the protocol that the packet
socket is bound to. Binding to ETH_P_IP is the right choice here.