This series began life as a modest attempt to fix two issues pertaining to VLANs nested inside Geneve tunnels and snowballed from there. The first issue, addressed by a simple one-liner, is that GSO is not enabled for upper VLAN devices on top of Geneve. The second issue, addressed by the balance of the series, deals largely with MTU handling. VLAN devices above L2 in L3 tunnels inherit the MTU of the underlying device. This causes IP fragmentation because the inner L2 cannot be expanded within the same maximum L3 size to accommodate the additional VLAN tag.
As a first attempt, a new flag was introduced to generalize what was already being done for MACsec devices. This flag was unconditionally set for all devices that have a size constrained L2, such as is the case for Geneve and VXLAN tunnel devices. This doesn't quite do the right thing, however, if the underlying device MTU happens to be configured to a lower MTU than is supported. Thus, the approach was further refined to set IFF_NO_VLAN_ROOM when changing MTU, based on whether the underlying device L2 still has room for VLAN tags, but stopping short of registering device notifiers to update upper device MTU whenever a lower device changes. VLAN devices will thus do the sensible thing if they are applied to an already configured device, but will not dynamically update whenever the underlying device's MTU is subsequently changed (this seemed a bridge too far). Aggregate devices presented the next challenge. Transitively propagating IFF_NO_VLAN_ROOM via bonds, teams and the like seemed similar in principle to the handling of IFF_XMIT_DST_RELEASE (only the opposite), but IFF_XMIT_DST_RELEASE_PERM evaded understanding. Ultimately this flag failed to justify its existence, allowing the new flag to take its place and avoid taking up the last bit in the enum. Finally, an audit of the other net devices in the tree was conducted to discover where else this new behavior may be appropriate. At this point it was also discovered that GRE devices would happily allow VLANs to be added even when L3 is being tunneled in L3, hence restricting VLANs to ARPHRD_ETHER devices. Between ARPHRD_ETHER and IFF_NO_VLAN_ROOM, it now seemed only a hop and a skip to eliminate NET_F_VLAN_CHALLENGED too, but alas there are still a few holdouts that would appear to require more of a moonshot to address. Edwin Peer (11): net: geneve: enable vlan offloads net: do away with the IFF_XMIT_DST_RELEASE_PERM flag net: vlan: add IFF_NO_VLAN_ROOM to constrain MTU net: geneve: constrain upper VLAN MTU using IFF_NO_VLAN_ROOM net: vxlan: constrain upper VLAN MTU using IFF_NO_VLAN_ROOM net: l2tp_eth: constrain upper VLAN MTU using IFF_NO_VLAN_ROOM net: gre: constrain upper VLAN MTU using IFF_NO_VLAN_ROOM net: distribute IFF_NO_VLAN_ROOM into aggregate devs net: ntb_netdev: support VLAN using IFF_NO_VLAN_ROOM net: vlan: disallow non-Ethernet devices net: leverage IFF_NO_VLAN_ROOM to limit NETIF_F_VLAN_CHALLENGED Documentation/networking/netdev-features.rst | 4 +- drivers/infiniband/ulp/ipoib/ipoib_main.c | 3 +- drivers/net/bonding/bond_main.c | 15 ++- drivers/net/ethernet/intel/e100.c | 15 ++- .../net/ethernet/mellanox/mlxsw/switchx2.c | 52 ++++++-- drivers/net/ethernet/toshiba/ps3_gelic_net.c | 12 +- drivers/net/ethernet/wiznet/w5100.c | 6 +- drivers/net/ethernet/wiznet/w5300.c | 6 +- drivers/net/ethernet/xilinx/ll_temac_main.c | 1 - drivers/net/geneve.c | 17 ++- drivers/net/ifb.c | 4 + drivers/net/loopback.c | 1 - drivers/net/macsec.c | 6 +- drivers/net/net_failover.c | 31 +++-- drivers/net/ntb_netdev.c | 8 +- drivers/net/rionet.c | 3 + drivers/net/sb1000.c | 1 + drivers/net/team/team.c | 16 +-- drivers/net/vrf.c | 4 +- drivers/net/vxlan.c | 10 +- drivers/net/wimax/i2400m/netdev.c | 5 +- drivers/s390/net/qeth_l2_main.c | 12 +- include/linux/if_vlan.h | 48 ++++++++ include/linux/netdevice.h | 12 +- net/8021q/vlan.c | 2 +- net/8021q/vlan_dev.c | 9 ++ net/8021q/vlan_netlink.c | 2 + net/core/dev.c | 2 +- net/ipv4/ip_tunnel.c | 2 + net/ipv6/ip6_gre.c | 4 +- net/l2tp/l2tp_eth.c | 114 ++++++++++-------- net/sched/sch_teql.c | 3 + 32 files changed, 290 insertions(+), 140 deletions(-) -- 2.26.2
