Subject: Re: WMM classification guideline for applications?
From: Johannes Berg <johannes@sipsolutions.net>
To: David Acker <dacker@roinet.com>
Cc: Kalle Valo <kalle.valo@iki.fi>, linux-wireless@vger.kernel.org,
	patrik.flykt@nokia.com
In-Reply-To: <4B1BF399.1020103@roinet.com>
References: <87d42u6dnd.fsf@purkki.valot.fi> <4B19276F.5080604@roinet.com>
	 <878wdi69u9.fsf@purkki.valot.fi>  <4B1933F5.2010408@roinet.com>
	 <1260096387.3461.2.camel@johannes.local>  <4B1BF399.1020103@roinet.com>
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Date: Sun, 06 Dec 2009 19:32:21 +0100
Message-ID: <1260124341.3461.22.camel@johannes.local>
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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:
> >=20
> >> I am not an expert on how the kernel handles vlans, but it appears tha=
t=20
> >> the priority field's value is set by the user space VLAN creation tool=
s=20
> >> through an ioctl with SET_VLAN_EGRESS_PRIORITY_CMD which calls=20
> >> 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=20
> >> priority field based on the skb priority field.
> >>
> >> In this case it would seem that skb priority and the vlan priority are=
=20
> >> both set and there may be a non-trivial mapping between the two.=20
> >=20
> > 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 t=
o
> > the skb->priority, if the administrator wishes to use it?
>=20
> You are correct on rx.

I don't see how RX matters at all, to mac80211?

>   The tricky part is the non-trivial mapping on=20
> tx.  If mac80211 only looks at the skb->priority and assumes priority 0=20
> means best effort, the code could be missing that skb->priority 0 maps=20
> to vlan priority 7.  If we define that mac80211 only looks at=20
> skb->priority, perhaps we should allow user space control of the mapping=20
> of the skb->priority to WMM priority queue.  This could be similar to=20
> the mapping capabilities in the VLAN code.  That way, an admin can make=20
> sure that the skb priority is mapped to both an appropriate vlan=20
> 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.

johannes

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