by Ido Schimmel

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Subject: Re: [PATCH v2 net-next 04/11] net: bridge: offload initial and final port flags through switchdev

On Thu, Feb 11, 2021 at 11:35:27AM +0200, Vladimir Oltean wrote:
> On Thu, Feb 11, 2021 at 09:44:43AM +0200, Ido Schimmel wrote:
> > On Thu, Feb 11, 2021 at 01:23:52AM +0200, Vladimir Oltean wrote:
> > > On Wed, Feb 10, 2021 at 12:59:49PM +0200, Ido Schimmel wrote:
> > > > > > The reverse, during unlinking, would be to refuse unlinking if the upper
> > > > > > has uppers of its own. netdev_upper_dev_unlink() needs to learn to
> > > > > > return an error and callers such as team/bond need to learn to handle
> > > > > > it, but it seems patchable.
> > > > >
> > > > > Again, this was treated prior to my deletion in this series and not by
> > > > > erroring out, I just really didn't think it through.
> > > > >
> > > > > So you're saying that if we impose that all switchdev drivers restrict
> > > > > the house of cards to be constructed from the bottom up, and destructed
> > > > > from the top down, then the notification of bridge port flags can stay
> > > > > in the bridge layer?
> > > >
> > > > I actually don't think it's a good idea to have this in the bridge in
> > > > any case. I understand that it makes sense for some devices where
> > > > learning, flooding, etc are port attributes, but in other devices these
> > > > can be {port,vlan} attributes and then you need to take care of them
> > > > when a vlan is added / deleted and not only when a port is removed from
> > > > the bridge. So for such devices this really won't save anything. I would
> > > > thus leave it to the lower levels to decide.
> > >
> > > Just for my understanding, how are per-{port,vlan} attributes such as
> > > learning and flooding managed by the Linux bridge? How can I disable
> > > flooding only in a certain VLAN?
> >
> > You can't (currently). But it does not change the fact that in some
> > devices these are {port,vlan} attributes and we are talking here about
> > the interface towards these devices. Having these as {port,vlan}
> > attributes allows you to support use cases such as a port being enslaved
> > to a VLAN-aware bridge and its VLAN upper(s) enslaved to VLAN unaware
> > bridge(s).
>
> I don't think I understand the use case really. You mean something like this?
>
> br1 (vlan_filtering=0)
> / \
> / \
> swp0.100 \
> | \
> |(vlan_filtering \
> | br0 =1) \
> | / \ \
> |/ \ \
> swp0 swp1 swp2
>
> A packet received on swp0 with VLAN tag 100 will go to swp0.100 which
> will be forwarded according to the FDB of br1, and will be delivered to
> swp2 as untagged? Respectively in the other direction, a packet received
> on swp2 will have a VLAN 100 tag pushed on egress towards swp0, even if
> it is already VLAN-tagged?
>
> What do you even use this for?

The more common use case is to have multiple VLAN-unaware bridges
instead of one VLAN-aware bridge. I'm not aware of users that use the
hybrid model (VLAN-aware + VLAN-unaware). But regardless, this entails
treating above mentioned attributes as {port,vlan} attributes. A device
that only supports them as port attributes will have problems supporting
such a model.

> And also: if the {port,vlan} attributes can be simulated by making the
> bridge port be an 8021q upper of a physical interface, then as far as
> the bridge is concerned, they still are per-port attributes, and they
> are per-{port,vlan} only as far as the switch driver is concerned -
> therefore I don't see why it isn't okay for the bridge to notify the
> brport flags in exactly the same way for them too.

Look at this hunk from the patch:

@@ -343,6 +360,8 @@ static void del_nbp(struct net_bridge_port *p)
update_headroom(br, get_max_headroom(br));
netdev_reset_rx_headroom(dev);

+ nbp_flags_notify(p, BR_PORT_DEFAULT_FLAGS & ~BR_LEARNING,
+ BR_PORT_DEFAULT_FLAGS);
nbp_vlan_flush(p);
br_fdb_delete_by_port(br, p, 0, 1);
switchdev_deferred_process();

Devices that treat these attributes as {port,vlan} attributes will undo
this change upon the call to nbp_vlan_flush() when all the VLANs are
flushed.

>
> > Obviously you need to ensure there is no conflict between the
> > VLANs used by the VLAN-aware bridge and the VLAN device(s).
>
> On the other hand I think I have a more real-life use case that I think
> is in conflict with this last phrase.
> I have a VLAN-aware bridge and I want to run PTP in VLAN 7, but I also
> need to add VLAN 7 in the VLAN table of the bridge ports so that it
> doesn't drop traffic. PTP is link-local, so I need to run it on VLAN
> uppers of the switch ports. Like this:
>
> ip link add br0 type bridge vlan_filtering 1
> ip link set swp0 master br0
> ip link set swp1 master br0
> bridge vlan add dev swp0 vid 7 master
> bridge vlan add dev swp1 vid 7 master
> bridge vlan add dev br0 vid 7 self
> ip link add link swp0 name swp0.7 type vlan id 7
> ip link add link swp1 name swp0.7 type vlan id 7
> ptp4l -i swp0.7 -i swp1.7 -m
>
> How can I do that considering that you recommend avoiding conflicts
> between the VLAN-aware bridge and 8021q uppers? Or is that true only
> when the 8021q uppers are bridged?

The problem is with the statement "I also need to add VLAN 7 in the VLAN
table of the bridge ports so that it doesn't drop traffic". Packets with
VLAN 7 received by swp0 will be processed by swp0.7. br0 is irrelevant
and configuring swp0.7 should be enough in order to enable the VLAN
filter for VLAN 7 on swp0. I don't know the internals of the HW you are
working with, but I imagine that you would need to create a HW bridge
between {swp0, VLAN 7} and the CPU port so that all the traffic with
VLAN 7 will be sent / flooded to the CPU.