Re: [RFC PATCH v2 net-next 03/16] net: dsa: inherit the actual bridge port flags at join time

[Vladimir Oltean <olteanv@gmail.com>]

On Fri, Mar 19, 2021 at 03:08:46PM -0700, Florian Fainelli wrote:
> 
> 
> On 3/18/2021 4:18 PM, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@nxp.com>
> > 
> > DSA currently assumes that the bridge port starts off with this
> > constellation of bridge port flags:
> > 
> > - learning on
> > - unicast flooding on
> > - multicast flooding on
> > - broadcast flooding on
> > 
> > just by virtue of code copy-pasta from the bridge layer (new_nbp).
> > This was a simple enough strategy thus far, because the 'bridge join'
> > moment always coincided with the 'bridge port creation' moment.
> > 
> > But with sandwiched interfaces, such as:
> > 
> >  br0
> >   |
> > bond0
> >   |
> >  swp0
> > 
> > it may happen that the user has had time to change the bridge port flags
> > of bond0 before enslaving swp0 to it. In that case, swp0 will falsely
> > assume that the bridge port flags are those determined by new_nbp, when
> > in fact this can happen:
> > 
> > ip link add br0 type bridge
> > ip link add bond0 type bond
> > ip link set bond0 master br0
> > ip link set bond0 type bridge_slave learning off
> > ip link set swp0 master br0
> > 
> > Now swp0 has learning enabled, bond0 has learning disabled. Not nice.
> > 
> > Fix this by "dumpster diving" through the actual bridge port flags with
> > br_port_flag_is_set, at bridge join time.
> > 
> > We use this opportunity to split dsa_port_change_brport_flags into two
> > distinct functions called dsa_port_inherit_brport_flags and
> > dsa_port_clear_brport_flags, now that the implementation for the two
> > cases is no longer similar.
> > 
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> > ---
> >  net/dsa/port.c | 123 ++++++++++++++++++++++++++++++++-----------------
> >  1 file changed, 82 insertions(+), 41 deletions(-)
> > 
> > diff --git a/net/dsa/port.c b/net/dsa/port.c
> > index fcbe5b1545b8..346c50467810 100644
> > --- a/net/dsa/port.c
> > +++ b/net/dsa/port.c
> > @@ -122,26 +122,82 @@ void dsa_port_disable(struct dsa_port *dp)
> >  	rtnl_unlock();
> >  }
> >  
> > -static void dsa_port_change_brport_flags(struct dsa_port *dp,
> > -					 bool bridge_offload)
> > +static void dsa_port_clear_brport_flags(struct dsa_port *dp,
> > +					struct netlink_ext_ack *extack)
> >  {
> >  	struct switchdev_brport_flags flags;
> > -	int flag;
> >  
> > -	flags.mask = BR_LEARNING | BR_FLOOD | BR_MCAST_FLOOD | BR_BCAST_FLOOD;
> > -	if (bridge_offload)
> > -		flags.val = flags.mask;
> > -	else
> > -		flags.val = flags.mask & ~BR_LEARNING;
> > +	flags.mask = BR_LEARNING;
> > +	flags.val = 0;
> > +	dsa_port_bridge_flags(dp, flags, extack);
> 
> Would not you want to use the same for_each_set_bit() loop that
> dsa_port_change_br_flags() uses, that would be a tad more compact.
> -- 
> Florian

The reworded version has an equal number of lines, but at least it
catches errors now:

static void dsa_port_clear_brport_flags(struct dsa_port *dp,
					struct netlink_ext_ack *extack)
{
	const unsigned long val = BR_FLOOD | BR_MCAST_FLOOD | BR_BCAST_FLOOD;
	const unsigned long mask = BR_LEARNING | BR_FLOOD | BR_MCAST_FLOOD |
				   BR_BCAST_FLOOD;
	int flag, err;

	for_each_set_bit(flag, &mask, 32) {
		struct switchdev_brport_flags flags = {0};

		flags.mask = BIT(flag);
		flags.val = val & BIT(flag);

		err = dsa_port_bridge_flags(dp, flags, extack);
		if (err && err != -EOPNOTSUPP)
			dev_err(dp->ds->dev,
				"failed to clear bridge port flag %d: %d (%pe)\n",
				flag, err, ERR_PTR(err));
	}
}