netdev - Re: [patch net-next v3 09/17] bridge: add API to notify bridge driver of learned FBD on offloaded device

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Date:	Tue, 25 Nov 2014 16:40:59 -1000
From:	Scott Feldman <sfeldma@...il.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	"nhorman@...driver.com" <nhorman@...driver.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Thomas Graf <tgraf@...g.ch>,
	"dborkman@...hat.com" <dborkman@...hat.com>,
	"ogerlitz@...lanox.com" <ogerlitz@...lanox.com>,
	"jesse@...ira.com" <jesse@...ira.com>,
	"pshelar@...ira.com" <pshelar@...ira.com>,
	"azhou@...ira.com" <azhou@...ira.com>,
	"ben@...adent.org.uk" <ben@...adent.org.uk>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"vyasevic@...hat.com" <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	"Fastabend, John R" <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	John Linville <linville@...driver.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	"ryazanov.s.a@...il.com" <ryazanov.s.a@...il.com>,
	"buytenh@...tstofly.org" <buytenh@...tstofly.org>,
	Aviad Raveh <aviadr@...lanox.com>,
	"nbd@...nwrt.org" <nbd@...nwrt.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Neil Jerram <Neil.Jerram@...aswitch.com>,
	"ronye@...lanox.com" <ronye@...lanox.com>,
	"simon.horman@...ronome.com" <simon.horman@...ronome.com>,
	"alexander.h.duyck@...hat.com" <alexander.h.duyck@...hat.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"mleitner@...hat.com" <mleitner@...hat.com>,
	Shrijeet Mukherjee <shrijeet@...il.com>,
	Andy Gospodarek <gospo@...ulusnetworks.com>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [patch net-next v3 09/17] bridge: add API to notify bridge driver
 of learned FBD on offloaded device

On Tue, Nov 25, 2014 at 4:34 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
> On 25/11/14 18:03, Scott Feldman wrote:
>> On Tue, Nov 25, 2014 at 12:44 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
>>> On 25/11/14 02:28, Jiri Pirko wrote:
>>>> From: Scott Feldman <sfeldma@...il.com>
>>>>
>>>> When the swdev device learns a new mac/vlan on a port, it sends some async
>>>> notification to the driver and the driver installs an FDB in the device.
>>>> To give a holistic system view, the learned mac/vlan should be reflected
>>>> in the bridge's FBD table, so the user, using normal iproute2 cmds, can view
>>>> what is currently learned by the device.  This API on the bridge driver gives
>>>> a way for the swdev driver to install an FBD entry in the bridge FBD table.
>>>> (And remove one).
>>>>
>>>> This is equivalent to the device running these cmds:
>>>>
>>>>   bridge fdb [add|del] <mac> dev <dev> vid <vlan id> master
>>>>
>>>> This patch needs some extra eyeballs for review, in paricular around the
>>>> locking and contexts.
>>>>
>>>> Signed-off-by: Scott Feldman <sfeldma@...il.com>
>>>> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
>>>> ---
>>>
>>> [snip]
>>>
>>>> +     head = &br->hash[br_mac_hash(addr, vid)];
>>>> +     fdb = fdb_find(head, addr, vid);
>>>> +     if (!fdb) {
>>>> +             fdb = fdb_create(head, p, addr, vid);
>>>> +             if (!fdb) {
>>>> +                     err = -ENOMEM;
>>>> +                     goto err_unlock;
>>>> +             }
>>>> +             fdb->added_by_external_learn = 1;
>>>> +             fdb_notify(br, fdb, RTM_NEWNEIGH);
>>>> +     } else if (fdb->added_by_external_learn) {
>>>> +             /* Refresh entry */
>>>> +             fdb->updated = fdb->used = jiffies;
>>>> +     } else if (!fdb->added_by_user) {
>>>> +             /* Take over SW learned entry */
>>>> +             fdb->added_by_external_learn = 1;
>>>> +             fdb->updated = jiffies;
>>>> +             fdb_notify(br, fdb, RTM_NEWNEIGH);
>>>> +     }
>>>
>>> Is there any case where this fdb entry gets re-used and is no longer
>>> added by an external learning? Should we clear this flag somewhere?
>>
>> Once the FDB entry is marked "added_by_external_learn" it stays marked
>> as such until removed by aging cleanup process (or flushed due to
>> interface down, etc).  If aged out (and now deleted), the FDB entry
>> may come back either by SW learn or by HW learn.  If SW learn comes
>> first, and then HW learn, HW learn will override and mark the existing
>> FDB entry "added_by_external_learn".  So there is take-over by HW but
>> no give-back to SW.  And there is no explicit clearing of the mark
>> short of deleting the FDB entry.  The mark is mostly for letting
>> user's know which FDB entries where learned by HW and synced to the
>> bridge's FDB.
>
> Thanks, makes sense now. This is probably obvious in this context, but
> maybe it would not hurt to come up with a documentation that describe
> the offload API, FDB entry lifetime and HW/SW ownership etc...

I have an updated Documentation/networking/switchdev.txt that covers
the swdev APIs and usage and notes, but Jiri is being stingy with it.
Will get this out, either in v4 or follow-on patches.  There is enough
going on just with L2 offload that we're going to need some good
documentation to guide implementers.
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