Re: [PATCH net-next 1/7] net: sched: Add a trap-and-forward action

On 2021-04-09 9:43 a.m., Petr Machata wrote:

Jamal Hadi Salim [off-list ref] writes:

quoted

quoted

quoted

Does the spectrum not support multiple actions?
e.g with a policy like:
   match blah action trap action drop skip_sw

Trap drops implicitly. We need a "trap, but don't drop". Expressed in
terms of existing actions it would be "mirred egress redirect dev
$cpu_port". But how to express $cpu_port except again by a HW-specific
magic token I don't know.

(I meant mirred egress mirror, not redirect.)

Ok.

quoted

Note: mirred was originally intended to send redirect/mirror
packets to user space (the comment is still there in the code).
Infact there is a patch lying around somewhere that does that with
packet sockets (the author hasnt been serious about pushing it
upstream). In that case the semantics are redirecting to a file
descriptor. Could we have something like that here which points
to whatever representation $cpu_port has? Sounds like semantics
for "trap and forward" are just "mirror and forward".

Hmm, we have devlink ports, the CPU port is exposed there. But that's
the only thing that comes to mind. Those are specific for the given
device though, it doesn't look suitable...

If it has an ifindex should be good enough for abstraction
purposes.

quoted

I think there is value in having something like trap action
which generalizes the combinations only to the fact that
it will make it easier to relay the info to the offload without
much transformation.
If i was to do it i would write one action configured by user space:
- to return DROP if you want action trap-and-drop semantics.
- to return STOLEN if you want trap
- to return PIPE if you want trap and forward. You will need a second
action composed to forward.

I think your STOLEN and PIPE are the same behavior. Both are "transfer
the packet to the SW datapath, but keep it in the HW datapath".

In general I have no issue expressing this stuff as a new action,
instead of an opcode. I'll take a look at this.

Ok, thanks.

cheers,
jamal