netdev - Re: [PATCH net-next v2 4/7] net: packet: use skb->dev as storage for skb orig len instead of skb->cb[]

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Message-ID: <CAHsH6Gv8Dh3RQ0V7KURcca9bzZGY0FwiqGj-mP9oKA_Vv72nUA@mail.gmail.com>
Date:	Sun, 1 Mar 2015 07:09:54 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	linux-bluetooth@...r.kernel.org,
	Marcel Holtmann <marcel@...tmann.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 4/7] net: packet: use skb->dev as storage for
 skb orig len instead of skb->cb[]

On Sat, Feb 28, 2015 at 11:00 PM, David Miller <davem@...emloft.net> wrote:
> From: Eyal Birger <eyal.birger@...il.com>
> Date: Sat, 28 Feb 2015 22:38:04 +0200
>
>> My concern is that any value I pick based on the existing implementations
>> would need to be adjusted come a protocol with a larger address length.
>
> Then we need a method that requires protocols to register their
> address length in a manner that will allow us to validate that
> limit at compile time.
>

Sorry to reiterate this, but such validation will inherently become the
actual limit for hardware addresses.
So, it would be equivalent to changing the in-kernel definition of
MAX_ADDR_SIZE.

Is this something to be considered?

> This is not rocket science.
>
> Right now we're proposing to do utterly stupid shit like encoding
> integers in device pointers in the sk_buff, when that is absolutely
> not necessary at all.

Ok. Another suggestion I received was to delay the preparation of the full
sockaddr_ll until it is needed, and store the skb original length in the first
two fields (sll_protocol and sll_family) as they can be derived later on from
the skb.

IMHO, It would still be somewhat of a hack though.

Would that approach be considered?

Regards,
Eyal.
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