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bridge: switchdev: Add forward mark support for stacked devices

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switchdev_port_fwd_mark_set() is used to set the 'offload_fwd_mark' of
port netdevs so that packets being flooded by the device won't be
flooded twice.

It works by assigning a unique identifier (the ifindex of the first
bridge port) to bridge ports sharing the same parent ID. This prevents
packets from being flooded twice by the same switch, but will flood
packets through bridge ports belonging to a different switch.

This method is problematic when stacked devices are taken into account,
such as VLANs. In such cases, a physical port netdev can have upper
devices being members in two different bridges, thus requiring two
different 'offload_fwd_mark's to be configured on the port netdev, which
is impossible.

The main problem is that packet and netdev marking is performed at the
physical netdev level, whereas flooding occurs between bridge ports,
which are not necessarily port netdevs.

Instead, packet and netdev marking should really be done in the bridge
driver with the switch driver only telling it which packets it already
forwarded. The bridge driver will mark such packets using the mark
assigned to the ingress bridge port and will prevent the packet from
being forwarded through any bridge port sharing the same mark (i.e.
having the same parent ID).

Remove the current switchdev 'offload_fwd_mark' implementation and
instead implement the proposed method. In addition, make rocker - the
sole user of the mark - use the proposed method.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ido Schimmel
2016-08-25 18:42:37 +02:00
committed by David S. Miller
parent 5c326ab49e
commit 6bc506b4fb
14 changed files with 117 additions and 132 deletions
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13
Documentation/networking/switchdev.txt
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@@ -283,15 +283,10 @@ be sent to the port netdev for processing by the bridge driver. The
bridge should not reflood the packet to the same ports the device flooded,
otherwise there will be duplicate packets on the wire.
To avoid duplicate packets, the device/driver should mark a packet as already
forwarded using skb->offload_fwd_mark. The same mark is set on the device
ports in the domain using dev->offload_fwd_mark. If the skb->offload_fwd_mark
is non-zero and matches the forwarding egress port's dev->skb_mark, the kernel
will drop the skb right before transmit on the egress port, with the
understanding that the device already forwarded the packet on same egress port.
The driver can use switchdev_port_fwd_mark_set() to set a globally unique mark
for port's dev->offload_fwd_mark, based on the port's parent ID (switch ID) and
a group ifindex.
To avoid duplicate packets, the switch driver should mark a packet as already
forwarded by setting the skb->offload_fwd_mark bit. The bridge driver will mark
the skb using the ingress bridge port's mark and prevent it from being forwarded
through any bridge port with the same mark.
It is possible for the switch device to not handle flooding and push the
packets up to the bridge driver for flooding. This is not ideal as the number