Johannes Berg wrote:
On Sun, 2009-12-06 at 13:10 -0500, David Acker wrote:
Johannes Berg wrote:
On Fri, 2009-12-04 at 11:08 -0500, David Acker wrote:
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.
But doesn't that also mean that mac80211 can happily ignore the VLAN
priority in the packet, because the vlan code will have propagated it to
the skb->priority, if the administrator wishes to use it?
You are correct on rx.
I don't see how RX matters at all, to mac80211?
When a packet is received on a higher priority WMM queue, should it
reflect that in skb->priority?
The tricky part is the non-trivial mapping on
tx. If mac80211 only looks at the skb->priority and assumes priority 0
means best effort, the code could be missing that skb->priority 0 maps
to vlan priority 7. If we define that mac80211 only looks at
skb->priority, perhaps we should allow user space control of the mapping
of the skb->priority to WMM priority queue. This could be similar to
the mapping capabilities in the VLAN code. That way, an admin can make
sure that the skb priority is mapped to both an appropriate vlan
priority and an appropriate WMM priority queue.
I don't understand. If I TX a packet, on a specific VLAN, then it'll go
through the VLAN code first, get 802.1q tags and then be passed to
mac80211, which ought be be fine with just looking at the priority value
the packet now got.
The packet will get tags which will contain the vlan priority mapped
from the original skb->priority. What if the administrator wanted all
applications that used a specific VLAN to have high priority. Without
having to change the applications, he could make the mapping of skb
priority 0 to go a high priority VLAN. It would be nice if he could
also make skb->priority 0 go to a high priority WMM queue. It is fine
to base every thing on the skb priority but it would be nice if the
mapping of skb priority to WMM queue was not static. It should have a
user space API that is similar in functionality to the VLAN priority API.
As an example, I have a system where a wireless router has multiple
SSIDs. One SSID is for guests and has little or no security and is on
VLAN 1 with a VLAN priority of 0. Another SSID is for system
configuration and has high security (802.11i) and is on VLAN 2 with a
VLAN priority of 7. The VLAN tagging is handled by the router; clients
send normal frames. Their applications do not require any changes. The
router will give higher priority to the system configuration VLAN during
any queuing. When the packets are sent, I have code (in madwifi in this
example) to put the packets with VLAN priority 0 in the best effort
queue while packets in vlan priority 7 go into the voice queue. This
code also sets the skb->priority field based on the VLAN priority. This
allows the queuing of the packet to the wifi0 device to reflect the
appropriate ordering. The router supports meshing such that the WMM
queues are used for packets between the routers. In this manner, the
QoS required for the higher priority VLAN is reflected through the whole
network, including the eventual wired destination.
To support this in mac80211, it would be nice to specify the mapping of
skb->priority to WMM queue on a per SSID basis. This would allow QoS to
be application driven or SSID driven.
-ack
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