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

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2012-06-06, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Wed, 2012-06-06 at 11:51 -0700, David Miller wrote:
>> From: Grant Edwards <grant.b.edwards@gmail.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.
>> 
>> 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.
>
> By the way, we had a similar problem, and the fix was :
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=a21d45726acacc963d8baddf74607d9b74e2b723
>
> Grant, depending on the context, you might use skb->avail_size and
> skb_availroom() as well.
>
> Beware skb->avail_size is unioned with skb->{mark|dropcount}

Thanks for the pointer.

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