netdev - Re: [RFC net-next] net: tc: flow indirect framework issue

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Date:   Wed, 13 Apr 2022 12:07:05 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Baowen Zheng <baowen.zheng@...igine.com>
Cc:     Mattias Forsblad <mattias.forsblad@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "roid@...dia.com" <roid@...dia.com>,
        "vladbu@...dia.com" <vladbu@...dia.com>,
        Eli Cohen <elic@...dia.com>, Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Tobias Waldekranz <tobias@...dekranz.com>
Subject: Re: [RFC net-next] net: tc: flow indirect framework issue

Hi Baowen,

On Wed, Apr 13, 2022 at 07:05:39AM +0000, Baowen Zheng wrote:
> Hi Mattias, in my understand, your problem may because you register
> your callback here. I am not sure why you choose to register your hook
> here(after the interface is added to the bridge to just trigger the
> callback in necessary case.)

> Then your function is called and add your cb to the tcf_block. But
> since the matchall filter has been created so you can not get your
> callback triggered. 

The bridge device has a certain lifetime, and the physical port device
has a different and completely independent lifetime. So the port device
may join the bridge when the bridge already has some filters on its
ingress chain.

Even with the indirect flow block callback registered at module load
stage as you suggest, the port driver needs to have a reason to
intercept a tc filter on a certain bridge. And when the port isn't a
member (yet) of that bridge, it has no reason to.

Of course, you could make the port driver speculatively monitor all tc
filters installed on all bridges in the system (related or unrelated to
ports belonging to this driver), just to not miss callbacks which may be
needed later. But that is quite suboptimal.

Mattias' question comes from the fact that there is already some logic
in flow_indr_dev_register() to replay missed flow block binding events,
added by Eli Cohen in commit 74fc4f828769 ("net: Fix offloading indirect
devices dependency on qdisc order creation"). That logic works, but it
replays only the binding, not the actual filters, which again, would be
necessary.

> Maybe you can try to regist your callback in your module load stage I
> think your callback will be triggered, or change the command order as: 
> tc qdisc add dev br0 clsact
> ip link set dev swp0 master br0
> tc filter add dev br0 ingress pref 1 proto all matchall action drop
> I am not sure whether it will take effect.

I think the idea is to make the given command order work, not to change it.