Re: [PATCH net-next 1/6] net: bridge: mdb: add MDB_FLAGS_STREAM_RESERVED flag

[Nikolay Aleksandrov <razor@blackwall.org>]

On 27/05/2026 03:42, Luke Howard wrote:
> Add a new MDB entry flag, MDB_FLAGS_STREAM_RESERVED, that userspace
> can set on RTM_NEWMDB to mark a multicast destination as belonging
> to a reserved stream (e.g. IEEE 802.1Q Stream Reservation Protocol /
> IEEE 1722 / TSN). The bridge core does no admission control on the
> basis of the flag; it is metadata propagated through switchdev to
> hardware drivers that can themselves enforce admission of AVB / SR
> priority traffic only to flagged destinations.
> 
> The flag is settable via the new nested attribute MDBE_ATTR_FLAGS
> (NLA_U32 bitmask, validated against MDB_FLAGS_SETTABLE_MASK), and is
> reflected in dump output via br_mdb_entry.flags as is done today for
> the OFFLOAD/BLOCKED/STAR_EXCL flags.
> 
> Assisted-by: Claude:claude-4.7-opus
> Signed-off-by: Luke Howard <lukeh@padl.com>
> ---
>   include/net/switchdev.h        |  4 ++++
>   include/uapi/linux/if_bridge.h |  2 ++
>   net/bridge/br_mdb.c            | 12 ++++++++++++
>   net/bridge/br_private.h        |  2 ++
>   net/bridge/br_switchdev.c      | 17 +++++++++++------
>   5 files changed, 31 insertions(+), 6 deletions(-)
> 

We don't add hw-only functionality, if you'd like to have this flag
you'll have to do a software implementation of this feature first.
Also please check the slop(code) that Claude generates before sending
it, there are obvious issues in this patch.

Cheers,
  Nik

> diff --git a/include/net/switchdev.h b/include/net/switchdev.h
> index ee500706496b0..03d176708b768 100644
> --- a/include/net/switchdev.h
> +++ b/include/net/switchdev.h
> @@ -111,10 +111,14 @@ struct switchdev_obj_port_vlan {
>   	container_of((OBJ), struct switchdev_obj_port_vlan, obj)
>   
>   /* SWITCHDEV_OBJ_ID_PORT_MDB */
> +
> +#define SWITCHDEV_MDB_F_STREAM_RESERVED		BIT(0)
> +
>   struct switchdev_obj_port_mdb {
>   	struct switchdev_obj obj;
>   	unsigned char addr[ETH_ALEN];
>   	u16 vid;
> +	u32 flags;
>   };
>   
>   #define SWITCHDEV_OBJ_PORT_MDB(OBJ) \
> diff --git a/include/uapi/linux/if_bridge.h b/include/uapi/linux/if_bridge.h
> index 21a700c02ef76..51ec314994bec 100644
> --- a/include/uapi/linux/if_bridge.h
> +++ b/include/uapi/linux/if_bridge.h
> @@ -705,6 +705,7 @@ struct br_mdb_entry {
>   #define MDB_FLAGS_STAR_EXCL		(1 << 2)
>   #define MDB_FLAGS_BLOCKED		(1 << 3)
>   #define MDB_FLAGS_OFFLOAD_FAILED	(1 << 4)
> +#define MDB_FLAGS_STREAM_RESERVED	(1 << 5)
>   	__u8 flags;
>   	__u16 vid;
>   	struct {
> @@ -760,6 +761,7 @@ enum {
>   	MDBE_ATTR_IFINDEX,
>   	MDBE_ATTR_SRC_VNI,
>   	MDBE_ATTR_STATE_MASK,
> +	MDBE_ATTR_FLAGS,
>   	__MDBE_ATTR_MAX,
>   };
>   #define MDBE_ATTR_MAX (__MDBE_ATTR_MAX - 1)
> diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
> index e0c7020b12f5f..1320ccd81b0a1 100644
> --- a/net/bridge/br_mdb.c
> +++ b/net/bridge/br_mdb.c
> @@ -146,6 +146,8 @@ static void __mdb_entry_fill_flags(struct br_mdb_entry *e, unsigned char flags)
>   		e->flags |= MDB_FLAGS_BLOCKED;
>   	if (flags & MDB_PG_FLAGS_OFFLOAD_FAILED)
>   		e->flags |= MDB_FLAGS_OFFLOAD_FAILED;
> +	if (flags & MDB_PG_FLAGS_STREAM_RESERVED)
> +		e->flags |= MDB_FLAGS_STREAM_RESERVED;
>   }
>   
>   static void __mdb_entry_to_br_ip(struct br_mdb_entry *entry, struct br_ip *ip,
> @@ -664,6 +666,7 @@ static const struct nla_policy br_mdbe_attrs_pol[MDBE_ATTR_MAX + 1] = {
>   						  MCAST_INCLUDE),
>   	[MDBE_ATTR_SRC_LIST] = NLA_POLICY_NESTED(br_mdbe_src_list_pol),
>   	[MDBE_ATTR_RTPROT] = NLA_POLICY_MIN(NLA_U8, RTPROT_STATIC),
> +	[MDBE_ATTR_FLAGS] = NLA_POLICY_MASK(NLA_U32, MDB_FLAGS_STREAM_RESERVED),
>   };
>   
>   static bool is_valid_mdb_source(struct nlattr *attr, __be16 proto,
> @@ -1072,6 +1075,8 @@ static int br_mdb_add_group(const struct br_mdb_config *cfg,
>   	if (entry->state == MDB_PERMANENT)
>   		flags |= MDB_PG_FLAGS_PERMANENT;
>   
> +	flags |= cfg->pg_flags;
> +
>   	if (br_multicast_is_star_g(&group))
>   		return br_mdb_add_group_star_g(cfg, mp, brmctx, flags, extack);
>   	else
> @@ -1225,6 +1230,13 @@ static int br_mdb_config_attrs_init(struct nlattr *set_attrs,
>   		cfg->rt_protocol = nla_get_u8(mdb_attrs[MDBE_ATTR_RTPROT]);
>   	}
>   
> +	if (mdb_attrs[MDBE_ATTR_FLAGS]) {
> +		u32 user_flags = nla_get_u32(mdb_attrs[MDBE_ATTR_FLAGS]);
> +
> +		if (user_flags & MDB_FLAGS_STREAM_RESERVED)
> +			cfg->pg_flags |= MDB_PG_FLAGS_STREAM_RESERVED;
> +	}
> +
>   	return 0;
>   }
>   
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 02671e648dac7..b9ee19448e38b 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -111,6 +111,7 @@ struct br_mdb_config {
>   	struct br_mdb_src_entry		*src_entries;
>   	int				num_src_entries;
>   	u8				rt_protocol;
> +	unsigned char			pg_flags;
>   };
>   #endif
>   
> @@ -317,6 +318,7 @@ struct net_bridge_fdb_flush_desc {
>   #define MDB_PG_FLAGS_STAR_EXCL		BIT(3)
>   #define MDB_PG_FLAGS_BLOCKED		BIT(4)
>   #define MDB_PG_FLAGS_OFFLOAD_FAILED	BIT(5)
> +#define MDB_PG_FLAGS_STREAM_RESERVED	BIT(6)
>   
>   #define PG_SRC_ENT_LIMIT	32
>   
> diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
> index 18b558a931ad9..bc05cda2f5350 100644
> --- a/net/bridge/br_switchdev.c
> +++ b/net/bridge/br_switchdev.c
> @@ -548,7 +548,8 @@ static void br_switchdev_mdb_complete(struct net_device *dev, int err, void *pri
>   }
>   
>   static void br_switchdev_mdb_populate(struct switchdev_obj_port_mdb *mdb,
> -				      const struct net_bridge_mdb_entry *mp)
> +				      const struct net_bridge_mdb_entry *mp,
> +				      const struct net_bridge_port_group *pg)
>   {
>   	if (mp->addr.proto == htons(ETH_P_IP))
>   		ip_eth_mc_map(mp->addr.dst.ip4, mdb->addr);
> @@ -560,6 +561,9 @@ static void br_switchdev_mdb_populate(struct switchdev_obj_port_mdb *mdb,
>   		ether_addr_copy(mdb->addr, mp->addr.dst.mac_addr);
>   
>   	mdb->vid = mp->addr.vid;
> +	mdb->flags = 0;
> +	if (pg && (pg->flags & MDB_PG_FLAGS_STREAM_RESERVED))
> +		mdb->flags |= SWITCHDEV_MDB_F_STREAM_RESERVED;
>   }
>   
>   static void br_switchdev_host_mdb_one(struct net_device *dev,
> @@ -575,7 +579,7 @@ static void br_switchdev_host_mdb_one(struct net_device *dev,
>   		},
>   	};
>   
> -	br_switchdev_mdb_populate(&mdb, mp);
> +	br_switchdev_mdb_populate(&mdb, mp, NULL);
>   
>   	switch (type) {
>   	case RTM_NEWMDB:
> @@ -622,6 +626,7 @@ static int br_switchdev_mdb_queue_one(struct list_head *mdb_list,
>   				      unsigned long action,
>   				      enum switchdev_obj_id id,
>   				      const struct net_bridge_mdb_entry *mp,
> +				      const struct net_bridge_port_group *pg,
>   				      struct net_device *orig_dev)
>   {
>   	struct switchdev_obj_port_mdb mdb = {
> @@ -632,7 +637,7 @@ static int br_switchdev_mdb_queue_one(struct list_head *mdb_list,
>   	};
>   	struct switchdev_obj_port_mdb *pmdb;
>   
> -	br_switchdev_mdb_populate(&mdb, mp);
> +	br_switchdev_mdb_populate(&mdb, mp, pg);
>   
>   	if (action == SWITCHDEV_PORT_OBJ_ADD &&
>   	    switchdev_port_obj_act_is_deferred(dev, action, &mdb.obj)) {
> @@ -671,7 +676,7 @@ void br_switchdev_mdb_notify(struct net_device *dev,
>   	if (!pg)
>   		return br_switchdev_host_mdb(dev, mp, type);
>   
> -	br_switchdev_mdb_populate(&mdb, mp);
> +	br_switchdev_mdb_populate(&mdb, mp, pg);
>   
>   	mdb.obj.orig_dev = pg->key.port->dev;
>   	switch (type) {
> @@ -740,7 +745,7 @@ br_switchdev_mdb_replay(struct net_device *br_dev, struct net_device *dev,
>   		if (mp->host_joined) {
>   			err = br_switchdev_mdb_queue_one(&mdb_list, dev, action,
>   							 SWITCHDEV_OBJ_ID_HOST_MDB,
> -							 mp, br_dev);
> +							 mp, NULL, br_dev);
>   			if (err) {
>   				spin_unlock_bh(&br->multicast_lock);
>   				goto out_free_mdb;
> @@ -754,7 +759,7 @@ br_switchdev_mdb_replay(struct net_device *br_dev, struct net_device *dev,
>   
>   			err = br_switchdev_mdb_queue_one(&mdb_list, dev, action,
>   							 SWITCHDEV_OBJ_ID_PORT_MDB,
> -							 mp, dev);
> +							 mp, p, dev);
>   			if (err) {
>   				spin_unlock_bh(&br->multicast_lock);
>   				goto out_free_mdb;