Re: Xtables2 Netlink spec

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On Mon, Dec 13, 2010 at 6:01 PM, Jan Engelhardt <jengelh@xxxxxxxxxx> wrote:
>
> On Thursday 2010-12-09 13:08, Pablo Neira Ayuso wrote:
>>
>>If we follow the one message per rule basis, you can put several
>>messages into one batch with different sequence numbers. Thus, you can
>>know what message in the batch has triggered the error and the reason.
>
> /* The unwritten laws of netlink */
>
> Normally, the sequence number of a response message is simply
> the one from the request message. But in a dump where there
> can be multiple messages, do they all share the sequence number?
>
> Must the response sequence numbers match at all, or is it like TCP
> where each side has its own set?
>
> BTW, can response messages - all those leading up to NLMSG_DONE -
> have different nlmsg_type, or not? Does the nlmsg_type need
> to match the request type?
>

There's an upper layer netlink flag set (NLM_F_MULTI , NLMSG_DONE,
etc) that's usually used in NETLINK_ROUTE, etc.

Essentially, you set the MULTI flag on multi-part messages, and DONE
on the last one, clients are expected to collect and respond;

In those cases, the sequence number does NOT change intra-messageset
in my experience, instead it is assumed they may be received out of
order.

> Jan
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