From: Petr Machata petrm@mellanox.com Date: Wed, 01 Aug 2018 00:35:53 +0200
After IPv4 packets are forwarded, the priority of the corresponding SKB is updated according to the TOS field of IPv4 header. This overrides any prioritization done earlier by e.g. an skbedit action or ingress-qos-map defined at a vlan device.
Such overriding may not always be desirable. Even if the packet ends up being routed, which implies this is an L3 network node, an administrator may wish to preserve whatever prioritization was done earlier on in the pipeline.
Therefore this patch set introduces a sysctl that controls this behavior, net.ipv4.ip_forward_update_priority. It's value is 1 by default to preserve the current behavior.
All of the above is implemented in patch #1.
Value changes prompt a new NETEVENT_IPV4_FWD_UPDATE_PRIORITY_UPDATE notification, so that the drivers can hook up whatever logic may depend on this value. That is implemented in patch #2.
In patches #3 and #4, mlxsw is adapted to recognize the sysctl. On initialization, the RGCR register that handles router configuration is set in accordance with the sysctl. The new notification is listened to and RGCR is reconfigured as necessary.
In patches #5 to #7, a selftest is added to verify that mlxsw reflects the sysctl value as necessary. The test is expressed in terms of the recently-introduced ieee_setapp support, and works by observing how DSCP value gets rewritten depending on packet priority. For this reason, the test is added to the subdirectory drivers/net/mlxsw. Even though it's not particularly specific to mlxsw, it's not suitable for running on soft devices (which don't support the ieee_setapp et.al.).
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