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

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Date:	Sun, 19 Jun 2016 17:27:02 +0300
From:	Saeed Mahameed <saeedm@....mellanox.co.il>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	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>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next 12/18] IB/mlx5: Add kernel offload flow-tag

On Sat, Jun 18, 2016 at 2:34 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> On Fri, Jun 17, 2016 at 3:31 PM, Saeed Mahameed
> <saeedm@....mellanox.co.il> wrote:
>>
>> 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.
>
> Well, your patch adds an extra test in kernel fast path, just to ease
> the life of people using kernel bypass,
> but willing to use tcpdump because they can not figure to do this in
> user space properly.
>
> Please find a way  _not_ adding a single instruction in kernel fast path.
>

Well, we can set skb->protocol = 0xffff.
what do you think ?