Re: [PATCH nf-next V2] netfilter: nft_queue: add _SREG_QNUM attr to select the queue number

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Wed, Sep 14, 2016 at 11:41:46PM +0800, Liping Zhang wrote:
> From: Liping Zhang <liping.zhang@spreadtrum.com>
> 
> Currently, the user can specify the queue numbers by _QUEUE_NUM and
> _QUEUE_TOTAL attributes, this is enough in most situations.
> 
> But acctually, it is not very flexible, for example:
>   tcp dport 80 mapped to queue0
>   tcp dport 81 mapped to queue1
>   tcp dport 82 mapped to queue2
> In order to do this thing, we must add 3 nft rules, and more
> mapping meant more rules ...
> 
> So take one register to select the queue number, then we can add one
> simple rule to mapping queues, maybe like this:
>   queue num tcp dport map { 80:0, 81:1, 82:2 ... }
> 
> Florian Westphal also proposed wider usage scenarios:
>   queue num jhash ip saddr . ip daddr mod ...
>   queue num meta cpu ...
>   queue num meta mark ...
> 
> The last point is how to load a queue number from sreg, although we can
> use *(u16*)&regs->data[reg] to load the queue number, just like nat expr
> to load its l4port do.
> 
> But we will cooperate with hash expr, meta cpu, meta mark expr and so on.
> They all store the result to u32 type, so cast it to u16 pointer and
> dereference it will generate wrong result in the big endian system.
> 
> So just keep it simple, we treat queue number as u32 type, although u16
> type is already enough.

Applied, thanks Liping.