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switchdev: update documentation for offload_fwd_mark 

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Scott Feldman 2015-07-18 18:24:52 -07:00 committed by David S. Miller
parent 3f98a8e636
commit a48037e7c6
1 changed files with 12 additions and 2 deletions
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14
Documentation/networking/switchdev.txt
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@ -279,8 +279,18 @@ and unknown unicast packets to all ports in domain, if allowed by port's
current STP state. The switch driver, knowing which ports are within which
vlan L2 domain, can program the switch device for flooding. The packet should
also 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.
XXX: the mechanism to avoid duplicate flood packets is being discuseed.
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.
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