Linux Ethernet Bridging - Aug 2022 - [Bridge] [PATCH v4 net-next 3/6] drivers: net: dsa: add locked fdb entry flag to drivers

On Mon, Aug 22, 2022 at 09:49:28AM +0200, netdev at kapio-technology.com
wrote:
> On 2022-08-22 07:40, Ido Schimmel wrote:
> > On Sun, Aug 21, 2022 at 03:43:04PM +0200, netdev at
kapio-technology.com
> > wrote:
> > 
> > I personally think that the mv88e6xxx semantics are very weird (e.g.,
no
> > roaming, traffic blackhole) and I don't want them to determine how
the
> > feature works in the pure software bridge or other hardware
> > implementations. On the other hand, I understand your constraints and
I
> > don't want to create a situation where user space is unable to
> > understand how the data path works from the bridge FDB dump with
> > mv88e6xxx.
> > 
> > My suggestion is to have mv88e6xxx report the "locked" entry
to the
> > bridge driver with additional flags that describe its behavior in
terms
> > of roaming, ageing and forwarding.
> > 
> > In terms of roaming, since in mv88e6xxx the entry can't roam you
should
> > report the entry with the "sticky" flag.
> 
> As I am not familiar with roaming in this context, I need to know how the
SW
> bridge should behave in this case.
I think I wasn't clear enough. The idea is to make the bridge compatible
with mv88e6xxx in a way that is discoverable by user space by having
mv88e6xxx add the locked entry with flags that describe the hardware
behavior. Therefore, it's not a matter of "how the SW bridge should
behave", but having it behave in a way that matches the offloaded data
path.
>From what I was able to understand from you, the "locked" entry
cannot
roam at all in mv88e6xxx, which can be described by the "sticky" flag.
> In this I am assuming that roaming is regarding unauthorized entries.
Yes, talking about "locked" entries that are notified by mv88e6xxx to
the bridge.
> In this case, is the roaming only between locked ports or does the
> roaming include that the entry can move to a unlocked port, resulting
> in the locked flag getting removed?
Any two ports. If the "locked" entry in mv88e6xxx cannot move once
installed, then the "sticky" flag accurately describes it.
> 
> > In terms of ageing, since
> > mv88e6xxx is the one doing the ageing and not the bridge driver,
report
> > the entry with the "extern_learn" flag.
> 
> Just for the record, I see that entries coming from the driver to the
bridge
> will always have the "extern learn" flag set as can be seen from
the
> SWITCHDEV_FDB_ADD_TO_BRIDGE events handling in br_switchdev_event() in
br.c,
> which I think is the correct behavior.
Yes.
> 
> > In terms of forwarding, in
> > mv88e6xxx the entry discards all matching packets. We can introduce a
> > new FDB flag that instructs the entry to silently discard all matching
> > packets. Like we have with blackhole routes and nexthops.
> 
> Any suggestions to the name of this flag?
I'm not good at naming, but "blackhole" is at least consistent
with what
we already have for routes and nexthop objects.
> 
> > 
> > I believe that the above suggestion allows you to fully describe how
> > these entries work in mv88e6xxx while keeping the bridge driver in
sync
> > with complete visibility towards user space.
> > 
> > It also frees the pure software implementation from the constraints of
> > mv88e6xxx, allowing "locked" entries to behave like any
other
> > dynamically learned entries modulo the fact that they cannot
"unlock" a
> > locked port.
> > 
> > Yes, it does mean that user space will get a bit different behavior
with
> > mv88e6xxx compared to a pure software solution, but a) It's only
the
> > corner cases that act a bit differently. As a whole, the feature works
> > largely the same. b) User space has complete visibility to understand
> > the behavior of the offloaded data path.
> > 
> 
> > > 
> > > I will change it in iproute2 to:
> > > bridge link set dev DEV mab on|off
> > 
> > And s/BR_PORT_MACAUTH/BR_PORT_MAB/ ?
> 
> Sure, I will do that. :-)
Thanks

On 2022-08-23 08:48, Ido Schimmel wrote:
> On Mon, Aug 22, 2022 at 09:49:28AM +0200, netdev at kapio-technology.com 
> wrote:
>> As I am not familiar with roaming in this context, I need to know how 
>> the SW
>> bridge should behave in this case.
> 
>> In this case, is the roaming only between locked ports or does the
>> roaming include that the entry can move to a unlocked port, resulting
>> in the locked flag getting removed?
> 
> Any two ports. If the "locked" entry in mv88e6xxx cannot move
once
> installed, then the "sticky" flag accurately describes it.
> 
But since I am also doing the SW bridge implementation without mv88e6xxx 
I need it to function according to needs.
Thus the locked entries created in the bridge I shall not put the sticky 
flag on, but there will be the situation where a locked entry can move 
to an unlocked port, which we regarded as a bug. In that case there is 
two possibilities, the locked entry can move to an unlocked port with 
the locked flag being removed or the locked entry can only move to 
another locked port?

On 2022-08-23 08:48, Ido Schimmel wrote:
> 
> I'm not good at naming, but "blackhole" is at least
consistent with
> what
> we already have for routes and nexthop objects.
> 
I have changed it the name "masked", as that is also the term used in 
the documentation for the zero-DPV entries, and I think that it will 
generally be a more accepted term.
Thus the name of the flag is now "BR_FDB_ENTRY_MASKED".

I hope that is fine with you?