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Vladimir Oltean bff33f7e2a net: dsa: implement auto-normalization of MTU for bridge hardware datapath 
Many switches don't have an explicit knob for configuring the MTU
(maximum transmission unit per interface).  Instead, they do the
length-based packet admission checks on the ingress interface, for
reasons that are easy to understand (why would you accept a packet in
the queuing subsystem if you know you're going to drop it anyway).

So it is actually the MRU that these switches permit configuring.

In Linux there only exists the IFLA_MTU netlink attribute and the
associated dev_set_mtu function. The comments like to play blind and say
that it's changing the "maximum transfer unit", which is to say that
there isn't any directionality in the meaning of the MTU word. So that
is the interpretation that this patch is giving to things: MTU == MRU.

When 2 interfaces having different MTUs are bridged, the bridge driver
MTU auto-adjustment logic kicks in: what br_mtu_auto_adjust() does is it
adjusts the MTU of the bridge net device itself (and not that of the
slave net devices) to the minimum value of all slave interfaces, in
order for forwarded packets to not exceed the MTU regardless of the
interface they are received and send on.

The idea behind this behavior, and why the slave MTUs are not adjusted,
is that normal termination from Linux over the L2 forwarding domain
should happen over the bridge net device, which _is_ properly limited by
the minimum MTU. And termination over individual slave devices is
possible even if those are bridged. But that is not "forwarding", so
there's no reason to do normalization there, since only a single
interface sees that packet.

The problem with those switches that can only control the MRU is with
the offloaded data path, where a packet received on an interface with
MRU 9000 would still be forwarded to an interface with MRU 1500. And the
br_mtu_auto_adjust() function does not really help, since the MTU
configured on the bridge net device is ignored.

In order to enforce the de-facto MTU == MRU rule for these switches, we
need to do MTU normalization, which means: in order for no packet larger
than the MTU configured on this port to be sent, then we need to limit
the MRU on all ports that this packet could possibly come from. AKA
since we are configuring the MRU via MTU, it means that all ports within
a bridge forwarding domain should have the same MTU.

And that is exactly what this patch is trying to do.

>From an implementation perspective, we try to follow the intent of the
user, otherwise there is a risk that we might livelock them (they try to
change the MTU on an already-bridged interface, but we just keep
changing it back in an attempt to keep the MTU normalized). So the MTU
that the bridge is normalized to is either:

 - The most recently changed one:

   ip link set dev swp0 master br0
   ip link set dev swp1 master br0
   ip link set dev swp0 mtu 1400

   This sequence will make swp1 inherit MTU 1400 from swp0.

 - The one of the most recently added interface to the bridge:

   ip link set dev swp0 master br0
   ip link set dev swp1 mtu 1400
   ip link set dev swp1 master br0

   The above sequence will make swp0 inherit MTU 1400 as well.

Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-03-27 16:07:25 -07:00
..
9p treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 188 2019-05-30 11:29:21 -07:00
bluetooth Bluetooth: Pause discovery and advertising during suspend 2020-03-11 18:03:49 +01:00
caif treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 194 2019-05-30 11:29:22 -07:00
iucv
netfilter netfilter: nf_tables: add nft_set_elem_update_expr() helper function 2020-03-15 15:27:49 +01:00
netns tcp: bind(0) remove the SO_REUSEADDR restriction when ephemeral ports are exhausted. 2020-03-12 12:08:09 -07:00
nfc NFC: Replace zero-length array with flexible-array member 2020-02-27 12:06:20 -08:00
phonet treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 336 2019-06-05 17:37:07 +02:00
sctp net: sctp: Replace zero-length array with flexible-array member 2020-02-29 21:52:19 -08:00
tc_act net: tc_skbedit: Make the skbedit priority offloadable 2020-03-19 21:09:19 -07:00
6lowpan.h 6lowpan: Replace zero-length array with flexible-array member 2020-02-28 14:51:30 +01:00
act_api.h net: sched: rename more stats_types 2020-03-23 20:54:23 -07:00
addrconf.h ipv6: Annotate ipv6_addr_is_* bitwise pointer casts 2019-12-16 16:09:44 -08:00
af_ieee802154.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
af_rxrpc.h afs: Fix client call Rx-phase signal handling 2020-03-13 23:04:35 +00:00
af_unix.h unix: uses an atomic type for scm files accounting 2020-02-28 12:12:53 -08:00
af_vsock.h vsock: add local transport support in the vsock core 2019-12-11 15:01:23 -08:00
ah.h
arp.h net: avoid potential false sharing in neighbor related code 2019-11-06 16:14:48 -08:00
atmclip.h
ax25.h
ax88796.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
bareudp.h net: Special handling for IP & MPLS. 2020-02-24 13:31:42 -08:00
bond_3ad.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 90 2019-05-24 17:37:53 +02:00
bond_alb.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 5 2019-05-21 11:28:40 +02:00
bond_options.h bonding: add an option to specify a delay between peer notifications 2019-07-04 12:30:48 -07:00
bonding.h bonding: Replace zero-length array with flexible-array member 2020-02-28 12:08:37 -08:00
bpf_sk_storage.h bpf: INET_DIAG support in bpf_sk_storage 2020-02-27 18:50:19 -08:00
busy_poll.h net: annotate lockless accesses to sk->sk_napi_id 2019-10-30 17:34:35 -07:00
calipso.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
cfg80211-wext.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
cfg80211.h cfg80211: Configure PMK lifetime and reauth threshold for PMKSA entries 2020-03-20 14:42:20 +01:00
cfg802154.h cfg802154: Replace zero-length array with flexible-array member 2020-02-29 14:39:08 +01:00
checksum.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
cipso_ipv4.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
cls_cgroup.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
codel.h
codel_impl.h
codel_qdisc.h
compat.h net: rework SIOCGSTAMP ioctl handling 2019-04-19 14:07:40 -07:00
datalink.h
dcbevent.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 201 2019-05-30 11:29:52 -07:00
dcbnl.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 201 2019-05-30 11:29:52 -07:00
devlink.h devlink: Add macro for "fw.mgmt.api" to info_get cb. 2020-03-27 15:34:42 -07:00
dn.h
dn_dev.h
dn_fib.h net: dn_fib: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
dn_neigh.h
dn_nsp.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 24 2019-05-21 11:52:39 +02:00
dn_route.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 24 2019-05-21 11:52:39 +02:00
drop_monitor.h drop_monitor: extend by passing cookie from driver 2020-02-25 11:05:54 -08:00
dsa.h net: dsa: implement auto-normalization of MTU for bridge hardware datapath 2020-03-27 16:07:25 -07:00
dsfield.h ipv6: Annotate bitwise IPv6 dsfield pointer cast 2019-12-16 16:09:44 -08:00
dst.h Remove DST_HOST 2020-03-23 21:57:44 -07:00
dst_cache.h
dst_metadata.h
dst_ops.h net: add bool confirm_neigh parameter for dst_ops.update_pmtu 2019-12-24 22:28:54 -08:00
erspan.h
esp.h
espintcp.h xfrm: add espintcp (RFC 8229) 2019-12-09 09:59:07 +01:00
ethoc.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
failover.h
fib_notifier.h ipv6: Remove old route notifications and convert listeners 2019-12-24 22:37:30 -08:00
fib_rules.h fib: add missing attribute validation for tun_id 2020-03-03 13:28:48 -08:00
firewire.h
flow.h route: Add multipath_hash in flowi_common to make user-define hash 2019-02-27 12:50:17 -08:00
flow_dissector.h net: sched: correct flower port blocking 2020-02-17 21:33:28 -08:00
flow_offload.h net: flow_offload.h: Fix a comment at flow_action_entry.mangle 2020-03-26 11:55:40 -07:00
fou.h
fq.h net/flow_dissector: switch to siphash 2019-10-23 20:13:22 -07:00
fq_impl.h net/fq_impl: Switch to kvmalloc() for memory allocation 2019-11-08 09:11:49 +01:00
garp.h treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
gen_stats.h net_sched: extend packet counter to 64bit 2019-11-05 18:20:55 -08:00
genetlink.h net: genetlink: remove unused genl_family_attrbuf() 2019-10-06 15:44:47 +02:00
geneve.h net: Move the definition of the default Geneve udp port to public header file 2019-03-22 12:09:31 -07:00
gre.h
gro_cells.h
gtp.h
gue.h net:gue.h:Fix shifting signed 32-bit value by 31 bits problem 2019-07-01 10:58:23 -07:00
hwbm.h net: hwbm: if CONFIG_NET_HWBM unset, make stub functions static 2019-10-25 16:24:32 -07:00
icmp.h icmp: introduce helper for nat'd source address in network device context 2020-02-13 14:19:00 -08:00
ieee80211_radiotap.h wireless-drivers-next patches for 5.1 2019-02-22 12:56:24 -08:00
ieee802154_netdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
if_inet6.h ipv6: shrink struct ipv6_mc_socklist 2019-08-28 14:43:03 -07:00
ife.h net: ife: drop include of module.h from net/ife.h 2019-04-22 21:50:53 -07:00
ila.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet6_connection_sock.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet6_hashtables.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet_common.h inet: factor out inet_send_prepare() 2019-07-03 13:51:54 -07:00
inet_connection_sock.h bpf: sockmap: Only check ULP for TCP sockets 2020-03-09 22:34:58 +01:00
inet_ecn.h
inet_frag.h inet: frags: re-introduce skb coalescing for local delivery 2019-08-08 15:55:10 -07:00
inet_hashtables.h tcp/dccp: fix possible race __inet_lookup_established() 2019-12-13 21:40:49 -08:00
inet_sock.h net: inet_sock: Replace zero-length array with flexible-array member 2020-03-02 11:16:28 -08:00
inet_timewait_sock.h tcp: honor SO_PRIORITY in TIME_WAIT state 2019-09-27 12:05:02 +02:00
inetpeer.h net: ipv4: use a dedicated counter for icmp_v4 redirect packets 2019-02-08 21:50:15 -08:00
ip.h inet: protect against too small mtu values. 2019-12-07 11:55:11 -08:00
ip6_checksum.h net: core: add helper tcp_v6_gso_csum_prep 2020-02-19 11:20:59 -08:00
ip6_fib.h Remove DST_HOST 2020-03-23 21:57:44 -07:00
ip6_route.h net: ip6_route: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
ip6_tunnel.h ip6_tunnel: allow not to count pkts on tstats by passing dev as NULL 2019-06-18 20:48:45 -04:00
ip_fib.h net: ip_fib: Replace zero-length array with flexible-array member 2020-03-02 11:16:28 -08:00
ip_tunnels.h treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
ip_vs.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-11-02 13:54:56 -07:00
ipcomp.h
ipconfig.h
ipv6.h net: UDP tunnel encapsulation module for tunnelling different protocols like MPLS, IP, NSH etc. 2020-02-24 13:31:42 -08:00
ipv6_frag.h inet: fix various use-after-free in defrags units 2019-06-19 11:37:47 -04:00
ipv6_stubs.h net: ipv6_stub: use ip6_dst_lookup_flow instead of ip6_dst_lookup 2019-12-04 12:27:13 -08:00
ipx.h bonding/alb: properly access headers in bond_alb_xmit() 2020-02-05 14:28:09 +01:00
iw_handler.h
kcm.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
l3mdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
lag.h
lapb.h
lib80211.h
llc.h
llc_c_ac.h
llc_c_ev.h
llc_c_st.h
llc_conn.h llc: fix sk_buff leak in llc_conn_service() 2019-10-08 13:23:05 -07:00
llc_if.h
llc_pdu.h
llc_s_ac.h
llc_s_ev.h
llc_s_st.h
llc_sap.h
lwtunnel.h net: lwtunnel: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
mac80211.h mac80211: update documentation about tx power 2020-03-20 14:42:19 +01:00
mac802154.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
macsec.h net: macsec: add support for getting offloaded stats 2020-03-26 20:17:36 -07:00
mip6.h net: mip6: Replace zero-length array with flexible-array member 2020-03-02 11:16:27 -08:00
mld.h net: ipv6: mld: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
mpls.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 295 2019-06-05 17:36:38 +02:00
mpls_iptunnel.h net: mpls: Replace zero-length array with flexible-array member 2020-02-28 12:08:37 -08:00
mptcp.h mptcp: Fix undefined mptcp_handle_ipv6_mapped for modular IPV6 2020-01-30 10:55:54 +01:00
mrp.h treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
ncsi.h
ndisc.h ipv6: ndisc: add support for 'PREF64' dns64 prefix identifier 2020-03-26 20:05:58 -07:00
neighbour.h neighbour: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
net_failover.h
net_namespace.h netns: Constify exported functions 2020-01-17 13:25:24 +01:00
net_ratelimit.h
netevent.h
netlabel.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
netlink.h netlink: rename nl80211_validate_nested() to nla_validate_nested() 2019-12-12 17:07:05 -08:00
netprio_cgroup.h netprio: use css ID instead of cgroup ID 2019-11-12 08:18:03 -08:00
netrom.h net: netrom: Fix error cleanup path of nr_proto_init 2019-04-11 13:59:49 -07:00
nexthop.h net: nexthop: Replace zero-length array with flexible-array member 2020-02-29 21:52:20 -08:00
nl802154.h
nsh.h
p8022.h
page_pool.h net: page_pool: API cleanup and comments 2020-02-20 10:09:25 -08:00
pie.h pie: realign comment 2020-03-04 13:25:55 -08:00
ping.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
pkt_cls.h net: sched: refine extack messages in tcf_change_indev 2020-03-26 19:52:31 -07:00
pkt_sched.h net_sched: add qdisc_watchdog_schedule_range_ns() 2020-03-17 21:16:34 -07:00
pptp.h
protocol.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
psample.h net: sched: take reference to psample group in flow_action infra 2019-09-16 09:18:03 +02:00
psnap.h
raw.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
rawv6.h
red.h net: sched: RED: Introduce an ECN nodrop mode 2020-03-14 21:03:46 -07:00
regulatory.h
request_sock.h net: add {READ|WRITE}_ONCE() annotations on ->rskq_accept_head 2019-10-09 21:34:31 -07:00
rose.h
route.h Remove DST_HOST 2020-03-23 21:57:44 -07:00
rsi_91x.h
rtnetlink.h
rtnh.h net: Rename net/nexthop.h net/rtnh.h 2019-04-22 21:47:25 -07:00
sch_generic.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-03-25 18:58:11 -07:00
scm.h
secure_seq.h
seg6.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
seg6_hmac.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
seg6_local.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
slhc_vj.h
smc.h net/smc: introduce bookkeeping of SMCD link groups 2019-11-15 12:28:28 -08:00
snmp.h net/tls: add skeleton of MIB statistics 2019-10-05 16:29:00 -07:00
sock.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2020-02-21 15:22:45 -08:00
sock_reuseport.h net: sock_reuseport: Replace zero-length array with flexible-array member 2020-02-29 21:52:19 -08:00
Space.h
stp.h
strparser.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
switchdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tcp.h bpf: sockmap: Move generic sockmap hooks from BPF TCP 2020-03-09 22:34:58 +01:00
tcp_states.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
timewait_sock.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tipc.h
tls.h net/tls: add helper for testing if socket is RX offloaded 2019-12-19 17:46:51 -08:00
tls_toe.h net/tls: rename tls_hw_* functions tls_toe_* 2019-10-04 14:07:07 -07:00
transp_v6.h
tso.h
tun_proto.h
udp.h bpf: Add sockmap hooks for UDP sockets 2020-03-09 22:34:58 +01:00
udp_tunnel.h ipv6: Move ipv6 stubs to a separate header file 2019-03-29 10:53:45 -07:00
udplite.h
vsock_addr.h vsock: remove include/linux/vm_sockets.h file 2019-11-14 18:12:17 -08:00
vxlan.h vxlan: add adjacent link to limit depth level 2019-10-24 14:53:49 -07:00
wext.h
wimax.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 268 2019-06-05 17:30:29 +02:00
x25.h net/x25: add new state X25_STATE_5 2019-12-09 10:28:43 -08:00
x25device.h
xdp.h xdp: page_pool related fix to cpumap 2019-06-19 11:23:13 -04:00
xdp_priv.h page_pool: do not release pool until inflight == 0. 2019-11-16 12:39:10 -08:00
xdp_sock.h xsk: ixgbe: i40e: ice: mlx5: Xsk_umem_discard_addr to xsk_umem_release_addr 2019-12-20 16:00:09 -08:00
xfrm.h xfrm: add espintcp (RFC 8229) 2019-12-09 09:59:07 +01:00