Re: [PATCH v2 0/3] Add NETIF_F_HW_BR_CAP feature

From: Andrew Lunn
Date: Mon Aug 26 2019 - 08:38:26 EST

On Mon, Aug 26, 2019 at 10:11:12AM +0200, Horatiu Vultur wrote:
> When a network port is added to a bridge then the port is added in
> promisc mode. Some HW that has bridge capabilities(can learn, forward,
> flood etc the frames) they are disabling promisc mode in the network
> driver when the port is added to the SW bridge.
> This patch adds the feature NETIF_F_HW_BR_CAP so that the network ports
> that have this feature will not be set in promisc mode when they are
> added to a SW bridge.
> In this way the HW that has bridge capabilities don't need to send all the
> traffic to the CPU and can also implement the promisc mode and toggle it
> using the command 'ip link set dev swp promisc on'

Hi Horatiu

I'm still not convinced this is needed. The model is, the hardware is
there to accelerate what Linux can do in software. Any peculiarities
of the accelerator should be hidden in the driver. If the accelerator
can do its job without needing promisc mode, do that in the driver.

So you are trying to differentiate between promisc mode because the
interface is a member of a bridge, and promisc mode because some
application, like pcap, has asked for promisc mode.

dev->promiscuity is a counter. So what you can do it look at its
value, and how the interface is being used. If the interface is not a
member of a bridge, and the count > 0, enable promisc mode in the
accelerator. If the interface is a member of a bridge, and the count >
1, enable promisc mode in the accelerator.