netdev - Re: [PATCH net-next v4 0/2] net: Introducing socket mark receive socket option

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Date:	Mon, 2 Mar 2015 15:48:58 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	David Miller <davem@...emloft.net>,
	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v4 0/2] net: Introducing socket mark receive
 socket option

On Mon, Mar 2, 2015 at 3:29 PM, Florian Westphal <fw@...len.de> wrote:
> Eyal Birger <eyal.birger@...il.com> wrote:
>> This patch set introduces a new socket option for fetching the mark
>> of skbs passed to sockets as ancillary data.
>>
>> A userspace program may wish to receive the mark of packets it
>> receives, for example for distinguishing between different TPROXY
>> diversion rules to the same userspace proxy socket.
>
> Hmm... Whats the use case?
> Even if you cannot use multiple sockets for every divert rule,
> TPROXY doesn't mangle payload; applications could use sockaddrs
> returned by accept, getpeername, getsockname etc.  to figure out
> which original port/address the packet was sent to?

Right. But that would mean the criteria for traffic diversion would need to
be known to the application receiving the traffic. IMHO It is a more elegant
solution to use the mark in order to distinguish between different traffic flows
instead of duplicating the match logic.

Also, the feature has use-cases outside of TPROXY as the skb->mark may be set
by other mechanisms (including SO_MARK from user space).

For example, a user space daemon can receive traffic from multiple
applications using
a single socket and distinguish between different traffic groups
according to the packet
mark.

Regards,
Eyal.
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