netdev - Re: [patch net-next v2 06/10] bridge: introduce fdb offloading via switchdev

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Message-ID: <20141110134715.GD4256@nanopsycho.orion>
Date:	Mon, 10 Nov 2014 14:47:15 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, nhorman@...driver.com,
	andy@...yhouse.net, tgraf@...g.ch, dborkman@...hat.com,
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	xiyou.wangcong@...il.com, john.r.fastabend@...el.com,
	edumazet@...gle.com, sfeldma@...il.com, f.fainelli@...il.com,
	roopa@...ulusnetworks.com, linville@...driver.com,
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	alexei.starovoitov@...il.com, Neil.Jerram@...aswitch.com,
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	alexander.h.duyck@...hat.com, john.ronciak@...el.com,
	mleitner@...hat.com, shrijeet@...il.com, gospo@...ulusnetworks.com,
	bcrl@...ck.org
Subject: Re: [patch net-next v2 06/10] bridge: introduce fdb offloading via
 switchdev

Mon, Nov 10, 2014 at 01:47:33PM CET, jhs@...atatu.com wrote:
>On 11/10/14 03:15, Jiri Pirko wrote:
>>Mon, Nov 10, 2014 at 04:47:48AM CET, jhs@...atatu.com wrote:
>>>On 11/09/14 05:51, Jiri Pirko wrote:
>>>>From: Scott Feldman <sfeldma@...il.com>
>>>>
>
>>Jamal, I believe we discussed this already.
>
>I cant remember how that ended.
>
>>The thing is that current
>>fdb_add/del does not need vlanid and master/self flags, because it
>>already has that (struct nlattr *tb[]). Here is the whole list of
>>parameters to these functions:
>>         NDA_DST,
>>         NDA_LLADDR,
>>         NDA_CACHEINFO,
>>         NDA_PROBES,
>>         NDA_VLAN,
>>         NDA_PORT,
>>         NDA_VNI,
>>         NDA_IFINDEX,
>>         NDA_MASTER,
>>
>>There are few problems in re-using this. It is netlink based so for calling
>>it from bridge code, we would have to construct netlink message. But
>>that could be probably changed.
>
>Trying to understand.
>
>A netlink message for a bridge to add an fdb is targeted at the
>*bridge port*.
>That message has semantic which says "please add this entry
>to the software bridge and/or offloaded hardware".
>If something is targetted at the bridge port, ->ndo_fdb_add()
>is invoked with an internally chewed structure.
>Why would you have to construct a new netlink message to the driver?

Because now, If you would like to pass one of NDA_DST, NDA_LLADDR,
NDA_CACHEINFO, NDA_PROBES, NDA_VLAN, NDA_PORT, NDA_VNI, NDA_IFINDEX,
NDA_MASTER values via ndo_fdb_add/del to the driver, you have to
construct "struct nlattr *tb[]". Preprocessing this tb into struct might
be suitable for some use-case, for some it may not.


>
>
>>As you can see from the list of parameters, this is no longer about fdb (addr,
>>vlanid) but this has been extended to something else.
>
>I am still missing understanding that part.
>Or maybe are you saying that you dont want to pass netlink
>constructs to the driver?

What I try to say is that the naming ndo_fdb_add/del is not accurate
because it is now used for far more than fdb (addr, vlan). See vxlan
code for example.


>
>>See vxlan code for
>>what this is used for. I believe that fdb_add/del should be renamed to
>>something else, perhaps l2neigh_add/del or something like that.
>>The other problem is that fdb_add/del is currently used by various
>>drivers for different purpose (adding macs to unicast list).
>>
>
>Ok, now a small spark ignited in my brain. You did talk about renaming
>things to neighXXX in one of the exchanges. I think this is a separate
>issue from the question of why you cant refactor ndo_fdb_add/del

It can be probably refactored in a way so it fits our fdb offloading
needs. I'm not really sure we would want it. ndo_fdb_* use-case
is dirrerent from what we introduce with ndo_sw_port_fdb_*. The only
similarity is the "fdb" name which in case of ndo_fdb_* is no longer
correct I believe.


>
>The abuse of using this interface for unicast addresses is probably
>driven by the fact some of the hardware probably offloads vlanid 0 or
>something speacial like 4095 to point to the underlying hardware that
>"this belongs to host cpu".
>I am not a fan of it (and have posted in exchanges with Vlad in the
>past).
>
>cheers,
>jamal
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