[RFC]: vlan priority handling in WMM

Dear mailing list,

I would like to manage the VLAN priority in Wireless QOS (WMM).

I get the VLAN tag from skb->vlan_tci and I extract the VLAN priority. 

How I should handle the priority value 0. 
	- Handle this value as no priority request, In this case the frame will 
		sent with the DSCP priority or default (Best effort)
	- Handle this value as a lowest priority, in this case I Map it to the WMM.

For your information, you can found below a discussion on this point 
with Johannes Berg.

Regards.

Cedric Voncken.

-----Message d'origine-----
De : Johannes Berg [mailto:johannes@sipsolutions.net]
Envoyé : lundi 8 juillet 2013 14:16
À : voncken
Cc : linux-wireless@vger.kernel.org
Objet : Re: [PATCH V2] vlan priority handling in WMM

On Mon, 2013-07-08 at 12:39 +0200, voncken wrote:

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The vlan Tag contain three bit for priority. The value 0 indicate

no

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priority (on this case the VLAN tag contain only VID). The

vlan_tci

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field is set to zero if the frame do not contain the vlan tag. So

if

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we have not a vlan tag or no priority in VLAN tag the priority

value

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is always 0.

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Yes but don't we know that the vlan_tci field is valid?

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I don't think you're correct in that 0 means "no priority present",

it actually means "best effort" as far as I can tell. Ignoring the 
VLAN tag when the field is 0 would mean we could use a higher priority 
from the contents of the frame, which would not be desired?

I can add a test with the macro vlan_tx_tag_present() to verify if the 
vlan_tci field is valid.
I test the value 0 to skip the VLAN priority and use the dscp priority 
in this case. The priority 0 in VLAN tag is often use to turn off the 
QOS, because not bit is allowed for it.

What do you mean by "is often used"? I don't see how that would be the case? Are you saying routers commonly ignore the VLAN priority value if it's 0? That would seem odd?

For me is it correct. Nevertheless, if you prefer, I can test only the 
vlan_tci validity and in this case always use the VLAN priority.

I don't know! Since you don't seem to really know either, we should ask somebody who knows, I think. Maybe you should Cc netdev with this question on the patch or so?

Sorry I made a mistake  0xE000 >>13 = 0x0007 and not 0x0003, and 7 is 
a 3 bits value.

Ah yes, I made the same mistake, sorry.

johannes