From: Patrick McHardy <kaber@trash•net>
To: Jan Engelhardt <jengelh@medozas•de>
Cc: "David S. Miller" <davem@davemloft•net>,
Holger Eitzenberger <heitzenberger@astaro•com>,
Pablo Neira Ayuso <pablo@netfilter•org>,
netdev@vger•kernel.org
Subject: Re: Netlink limitations
Date: Tue, 09 Nov 2010 13:24:26 +0100 [thread overview]
Message-ID: <4CD93D7A.2010305@trash.net> (raw)
In-Reply-To: <alpine.LNX.2.01.1011091303250.21752@obet.zrqbmnf.qr>
Am 09.11.2010 13:10, schrieb Jan Engelhardt:
>
> 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?
As I said, the basic idea is to use a length value of zero to indicate
that the length should be read from a second length member. Basically:
struct nlattr32 {
__u16 nla_len;
__u16 nla_type;
__u32 nla_len2;
};
prev parent reply other threads:[~2010-11-09 12:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-07 16:44 Netlink limitations Jan Engelhardt
2010-11-07 17:17 ` Patrick McHardy
2010-11-08 15:16 ` Thomas Graf
2010-11-08 19:21 ` Jan Engelhardt
2010-11-08 23:36 ` Pablo Neira Ayuso
2010-11-09 9:27 ` Patrick McHardy
2010-11-09 14:49 ` Thomas Graf
2010-11-09 20:20 ` Jan Engelhardt
2010-11-09 21:40 ` Thomas Graf
2010-11-09 22:02 ` Jan Engelhardt
2010-11-09 23:35 ` Thomas Graf
2010-11-09 23:42 ` Jan Engelhardt
2010-11-09 23:54 ` Thomas Graf
2010-11-09 11:58 ` Jan Engelhardt
2010-11-09 12:10 ` Jan Engelhardt
2010-11-09 12:24 ` Patrick McHardy [this message]
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