Re: [PATCH net-next,RFC 0/9] net: sched: prepare to reuse per-block callbacks from netfilter

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Fri, Apr 26, 2019 at 04:32:58PM +0200, Jiri Pirko wrote:
> Fri, Apr 26, 2019 at 02:33:37AM CEST, pablo@netfilter.org wrote:
> >Hi,
> >
> >This patchset aims to introduce changes to reuse the existing .ndo_setup_tc
> >netdev operations from netfilter.
> >
> >The idea is to move tcf_block_cb to net/core/flow_offload.c and rename
> >it to flow_block_cb. This object provides the minimal infrastructure to
> >set up per-block callbacks that are called to offload policies to
> >hardware.
> >
> >The tcf_block object is specific for TC to share policies between
> >ingress devices. This object has a list of tcf_block_cb objects that are
> >called to offload the policies to hardware. In netfilter, the idea is to
> >store the list of tcf_block_cb objects in a chain that would be bound to
> >several devices, eg.
> >
> >  chain x {
> >	type filter hook ingress devices = { eth0, eth1 } priority 0;
> >	...
> >  }
> >
> 
> Do you have the follow-up patchset somewhere? I'm curius about your
> goal. Without that, it is hard to understand what you are getting at.

Goal is to use the TC_SETUP_BLOCK logic in the existing drivers from
netfilter. So Netfilter calls TC_SETUP_BLOCK by when a chain is set up
to configure the driver, hence reuse your whole logic with minimal
changes.

Currently, the tcf_block_cb_register() call assumes there's a
tcf_block object in place and it internally invokes the tc
.reoffload() callback. This tcf_block corresponds to the nft_chain
object in netfilter, and I need to add my own .reoffload() callback
for the nft_chain object. This patch uses the block_index instead from
the driver, instead of exposing tcf_block.

This patchset updates the TC_SETUP_BLOCK path to only configure the
block_cb objects. The registration is done from the core, by iterating
the list of block_cb's that the driver offers in the temporary
tc_block_offload->cb_list, and then iterate over that list and
register them from the core.

My patchset moves the tcf_block_cb object to net/core/flow_offload.c
(it renames it to flow_block_cb) so it can be used both by tc and
netfilter.

Follow up patchset in netfilter calls TC_SETUP_BLOCK when the offloadi
flag is set on. Then, it has its own version of tc_setup_cb_call(),
which iterates over the block_cb() in this chain to reuse existing
driver codebase.

> >Hence, this emulates the shared blocks available in TC that Jiri made.
> >
> >Note that the list of tcf_block_cb objects will be called to offload
> >policies in this chain.
> 
> So you are going to use chain_id (if there is anything like that) as
> block_index during offload, right?

Yes. But I don't need to expose this chain_index to userspace though,
I can internally allocate it, I only need to make sure it does not
overlap with any of the existing tc block_indexed. I can just use a
different index space which does not overlap with the tc block index
space.

Thanks.