netdev - Re: Change in alloc_skb() behavior in 3.2+ kernels?

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Date:	Wed, 6 Jun 2012 19:01:40 +0000 (UTC)
From:	Grant Edwards <grant.b.edwards@...il.com>
To:	netdev@...r.kernel.org
Subject: Re: Change in alloc_skb() behavior in 3.2+ kernels?

On 2012-06-06, David Miller <davem@...emloft.net> wrote:
> From: Grant Edwards <grant.b.edwards@...il.com>
> Date: Wed, 6 Jun 2012 18:32:57 +0000 (UTC)
>
>> The kernel module that's started failing fills the allocated sk_buff
>> until tailroom() indicates it is full and then sends it.  The problem
>> is that sending a packet with a length of 1850 won't work (it's a
>> MAC-layer Ethernet packet).
>
> The amount of tailroom an SKB has is implementation dependent.

Today, that's apparently the case, but that's not what the man page
for alloc_skb said when the code was written.

> It's incredibly poor form to rely upon it to determine whether a fully
> sized frame has been constructed or not.
>
> Please fix the code that does this.

That's what I'll do as soon as I can find a definition of what the API
for alloc_skb() actually _is_.  It has clearly changed in the past few
years.

-- 
Grant Edwards               grant.b.edwards        Yow! I'm also against
                                  at               BODY-SURFING!!
                              gmail.com            

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