netdev - Re: Netlink limitations

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Date:	Tue, 9 Nov 2010 13:10:53 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Patrick McHardy <kaber@...sh.net>
cc:	"David S. Miller" <davem@...emloft.net>,
	Holger Eitzenberger <heitzenberger@...aro.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	netdev@...r.kernel.org
Subject: Re: Netlink limitations


On Sunday 2010-11-07 18:17, Patrick McHardy wrote:
>On 07.11.2010 17:44, Jan Engelhardt wrote:
>> we mentioned it only briefly at the Netfilter workshop a few weeks ago, 
>> but as I am trying to figure out how to use Netlink in Xtables, 
>> Netlink's limitations really start ruining my day.
>> 
>> The well-known issue is that NL messages[sic] the kernel is supposed to 
>> receive have a max size of 64K, due to nlmsghdr's use of uint16_t. This 
>> is very problematic because attributes can easily amass more than 64K. 
>> Think of a chain full of rules, represented by a top-level attribute 
>> that nests attributes. The problem is bidirectional, a table 
>> dump has the same problem.
>
>Messages are not limited to 64k, individual attributes are. Holger
>started working on a nlattr32, which uses 32 bit for the length
>value.

Does he have a format specification available?
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