netdev - Re: [PATCH net-next v4] net: qualcomm: rmnet: Add side band flow control support

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Date: Mon, 9 Oct 2023 19:42:51 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com>
Cc: davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 netdev@...r.kernel.org, vadim.fedorenko@...ux.dev, lkp@...el.com,
 horms@...nel.org, Sean Tranchetti <quic_stranche@...cinc.com>
Subject: Re: [PATCH net-next v4] net: qualcomm: rmnet: Add side band flow
 control support

On Thu,  5 Oct 2023 17:16:14 -0700 Subash Abhinov Kasiviswanathan wrote:
> Individual rmnet devices map to specific network types such as internet,
> multimedia messaging services, IP multimedia subsystem etc. Each of
> these network types may support varying quality of service for different
> bearers or traffic types.
> 
> The physical device interconnect to radio hardware may support a
> higher data rate than what is actually supported by the radio network.
> Any packets transmitted to the radio hardware which exceed the radio
> network data rate limit maybe dropped. This patch tries to minimize the
> loss of packets by adding support for bearer level flow control within a
> rmnet device by ensuring that the packets transmitted do not exceed the
> limit allowed by the radio network.
> 
> In order to support multiple bearers, rmnet must be created as a
> multiqueue TX netdevice. Radio hardware communicates the supported
> bearer information for a given network via side band signalling.
> Consider the following mapping -
> 
> IPv4 UDP port 1234 - Mark 0x1001 - Queue 1
> IPv6 TCP port 2345 - Mark 0x2001 - Queue 2
> 
> iptables can be used to install filters which mark packets matching these
> specific traffic patterns and the RMNET_QUEUE_MAPPING_ADD operation can
> then be to install the mapping of the mark to the specific txqueue.

I don't understand why you need driver specific commands to do this.
It should be easily achievable using existing TC qdisc infra.
What's the gap?