Kalle Valo wrote:
David Acker <dacker@xxxxxxxxxx> writes:
What do think of also supporting a method 4, VLAN priority field (0-7)?
Sorry, I haven't heard about this. I don't even know how applications
should set this. Can you show an example, please?
Sure. A system could be setup with multiple VLANs available on its
outgoing port. Imagine eth0.1, eth0.2 and eth0.7. Each one is a
different VLAN with a different priority mapping setup. The application
can use the high priority VLAN which should then be reflected in the
over the air packets using a high priority WMM queue. If the driver
implements the appropriate VLAN functionality it should be able to
detect VLAN tagged packets and pick the appropriate WMM hardware queue.
I think a driver can use vlan_get_tag to get the Tag Control
Information (TCI) field. The TCI field contains a 3-bit Priority Code
Point (PCP) field for 8 different priorities.
I am not an expert on how the kernel handles vlans, but it appears that
the priority field's value is set by the user space VLAN creation tools
through an ioctl with SET_VLAN_EGRESS_PRIORITY_CMD which calls
vlan_dev_set_egress_priority to map an skb priority to a vlan priority.
vlan_dev_hard_header then uses this information to populate the vlan
priority field based on the skb priority field.
In this case it would seem that skb priority and the vlan priority are
both set and there may be a non-trivial mapping between the two.
pkt_sched.h defines some skb priorities but also leaves many undefined.
The skb->priority is also larger then the vlan priority. If both are
set, which will take precedence?
-ack
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