netdev - Re: [PATCH net-next 12/18] IB/mlx5: Add kernel offload flow-tag

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Date:	Sat, 18 Jun 2016 01:31:26 +0300
From:	Saeed Mahameed <saeedm@....mellanox.co.il>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Saeed Mahameed <saeedm@...lanox.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Doug Ledford <dledford@...hat.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Maor Gottlieb <maorg@...lanox.com>,
	Huy Nguyen <huyn@...lanox.com>, Tal Alon <talal@...lanox.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next 12/18] IB/mlx5: Add kernel offload flow-tag

On Fri, Jun 17, 2016 at 7:00 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Fri, Jun 17, 2016 at 05:43:53PM +0300, Saeed Mahameed wrote:
>> From: Maor Gottlieb <maorg@...lanox.com>
>>
>> Add kernel offload flow tag for packets that will bypass the kernel
>> stack, e.g (RoCE/RDMA/RAW ETH (DPDK), etc ..).
>
> so the whole series is an elaborate way to enable dpdk? how nice.

NO, God forbids! the whole series has nothing to do with dpdk!
Please read the cover letter.

Quoting my own words from the cover letter:
"This patch set introduces mlx5 RoCE/RDMA packet sniffer, it allows
mlx5e netdevice to receive RoCE/RDMA or RAW ETH traffic which isn't
supposed to be passed to the kernel stack, for sniffing and diagnostics
purposes."

We simply want to selectively be able to see RoCE/RDMA ETH standard
traffic in tcpdump, for diagnostic purposes.
so in order to not overwhelm the kernel TCP/IP stack with this
traffic, this patch in particular
configures ConnectX4 hardware to tag those packets, so in downstream
patches mlx5 netdevice will mark the SKBs of those packets
to skip the TCP/IP stack and go only to tcpdump.

DPDK is not enabled/disabled or even slightly affected in this series.
It was just given as an example in this patch commit message for
traffic that can be sniffed in standard tools such as tcpdump.

Today there are some bad usages and abuse to skb->protocol where some
device drivers set skb->protocol = 0xffffff to skip the kernel TCP/IP
processing for the same diagnostic purposes.
In this series we are just trying to do the right thing.