linux-kernel - Re: [PATCH] net: preserve IP control block during GSO segmentation

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Message-ID: <CAM_iQpUO4aE_UybNYrFw+u=LWnF3OcC5jQ+ADsK1XobjBwUeEA@mail.gmail.com>
Date:	Mon, 11 Jan 2016 16:58:24 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Zang MingJie <zealot0630@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	dev@...nvswitch.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: preserve IP control block during GSO segmentation

On Sun, Jan 10, 2016 at 11:45 PM, Zang MingJie <zealot0630@...il.com> wrote:
> On 01/08/2016 08:13 PM, David Laight wrote:
>>
>> You could set SKB_SGO_CB_OFFSET to sizeof ((skb)->cb) - sizeof (struct
>> skb_gso_cb)
>> so that the end of 'cb' is always used.
>> (Assuming the former is a multiple of 4.)
>>
>> It might be worth using an on-stack structure passed through as a separate
>> parameter - it doesn't look as though it has to be queued with the skb.
>> (Clearly a bigger change.)
>
>
> I would definitely prefer the stack structure.
>
> As a kernel developer, sometime I can hardly figure out which struct current
> cb is without debug it, and the worst they are not documented anywhere. I
> can hardly know the life time of the cb types.

NAK.

Skb control block was not designed to be used like a stack but like a union
for different layers, just that people begin to mess it up.