Message-ID: <1380191899.3716.31.camel@ubuntu-vm-makita>
Date:	Thu, 26 Sep 2013 19:38:19 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	vyasevic@...hat.com
Cc:	Toshiaki Makita <toshiaki.makita1@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net 0/4] bridge: Fix problems around the PVID

On Tue, 2013-09-24 at 13:55 -0400, Vlad Yasevich wrote:
> On 09/24/2013 01:30 PM, Toshiaki Makita wrote:
> > On Tue, 2013-09-24 at 09:35 -0400, Vlad Yasevich wrote:
> >> On 09/24/2013 07:45 AM, Toshiaki Makita wrote:
> >>> On Mon, 2013-09-23 at 10:41 -0400, Vlad Yasevich wrote:
> >>>> On 09/17/2013 04:12 AM, Toshiaki Makita wrote:
> >>>>> On Mon, 2013-09-16 at 13:49 -0400, Vlad Yasevich wrote:
> >>>>>> On 09/13/2013 08:06 AM, Toshiaki Makita wrote:
> >>>>>>> On Thu, 2013-09-12 at 16:00 -0400, David Miller wrote:
> >>>>>>>> From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> >>>>>>>> Date: Tue, 10 Sep 2013 19:27:54 +0900
> >>>>>>>>
> >>>>>>>>> There seem to be some undesirable behaviors related with PVID.
> >>>>>>>>> 1. It has no effect assigning PVID to a port. PVID cannot be applied
> >>>>>>>>> to any frame regardless of whether we set it or not.
> >>>>>>>>> 2. FDB entries learned via frames applied PVID are registered with
> >>>>>>>>> VID 0 rather than VID value of PVID.
> >>>>>>>>> 3. We can set 0 or 4095 as a PVID that are not allowed in IEEE 802.1Q.
> >>>>>>>>> This leads interoperational problems such as sending frames with VID
> >>>>>>>>> 4095, which is not allowed in IEEE 802.1Q, and treating frames with VID
> >>>>>>>>> 0 as they belong to VLAN 0, which is expected to be handled as they have
> >>>>>>>>> no VID according to IEEE 802.1Q.
> >>>>>>>>>
> >>>>>>>>> Note: 2nd and 3rd problems are potential and not exposed unless 1st problem
> >>>>>>>>> is fixed, because we cannot activate PVID due to it.
> >>>>>>>>
> >>>>>>>> Please work out the issues in patch #2 with Vlad and resubmit this
> >>>>>>>> series.
> >>>>>>>>
> >>>>>>>> Thank you.
> >>>>>>>
> >>>>>>> I'm hovering between whether we should fix the issue by changing vlan 0
> >>>>>>> interface behavior in 8021q module or enabling a bridge port to sending
> >>>>>>> priority-tagged frames, or another better way.
> >>>>>>>
> >>>>>>> If you could comment it, I'd appreciate it :)
> >>>>>>>
> >>>>>>>
> >>>>>>> BTW, I think what is discussed in patch #2 is another problem about
> >>>>>>> handling priority-tags, and it exists without this patch set applied.
> >>>>>>> It looks like that we should prepare another patch set than this to fix
> >>>>>>> that problem.
> >>>>>>>
> >>>>>>> Should I include patches that fix the priority-tags problem in this
> >>>>>>> patch set and resubmit them all together?
> >>>>>>>
> >>>>>>
> >>>>>> I am thinking that we might need to do it in bridge and it looks like
> >>>>>> the simplest way to do it is to have default priority regeneration table
> >>>>>> (table 6-5 from 802.1Q doc).
> >>>>>>
> >>>>>> That way I think we would conform to the spec.
> >>>>>>
> >>>>>> -vlad
> >>>>>
> >>>>> Unfortunately I don't think the default priority regeneration table
> >>>>> resolves the problem because IEEE 802.1Q says that a VLAN-aware bridge
> >>>>> can transmit untagged or VLAN-tagged frames only (the end of section 7.5
> >>>>> and 8.1.7).
> >>>>>
> >>>>> No mechanism to send priority-tagged frames is found as far as I can see
> >>>>> the standard. I think the regenerated priority is used for outgoing PCP
> >>>>> field only if egress policy is not untagged (i.e. transmitting as
> >>>>> VLAN-tagged), and unused if untagged (Section 6.9.2 3rd/4th Paragraph).
> >>>>>
> >>>>> If we want to transmit priority-tagged frames from a bridge port, I
> >>>>> think we need to implement a new (optional) feature that is above the
> >>>>> standard, as I stated previously.
> >>>>>
> >>>>> How do you feel about adding a per-port policy that enables a bridge to
> >>>>> send priority-tagged frames instead of untagged frames when egress
> >>>>> policy for the port is untagged?
> >>>>> With this change, we can transmit frames for a given vlan as either all
> >>>>> untagged, all priority-tagged or all VLAN-tagged.
> >>>>
> >>>> That would work.  What I am thinking is that we do it by special casing
> >>>> the vid 0 egress policy specification.  Let it be untagged by default
> >>>> and if it is tagged, then we preserve the priority field and forward
> >>>> it on.
> >>>>
> >>>> This keeps the API stable and doesn't require user/admin from knowing
> >>>> exactly what happens.  Default operation conforms to the spec and allows
> >>>> simple change to make it backward-compatible.
> >>>>
> >>>> What do you think.  I've done a simple prototype of this an it seems to
> >>>> work with the VMs I am testing with.
> >>>
> >>> Are you saying that
> >>> - by default, set the 0th bit of untagged_bitmap; and
> >>> - if we unset the 0th bit and set the "vid"th bit, we transmit frames
> >>> classified as belonging to VLAN "vid" as priority-tagged?
> >>>
> >>> If so, though it's attractive to keep current API, I'm worried about if
> >>> it could be a bit confusing and not intuitive for kernel/iproute2
> >>> developers that VID 0 has a special meaning only in the egress policy.
> >>> Wouldn't it be better to adding a new member to struct net_port_vlans
> >>> instead of using VID 0 of untagged_bitmap?
> >>>
> >>> Or are you saying that we use a new flag in struct net_port_vlans but
> >>> use the BRIDGE_VLAN_INFO_UNTAGGED bit with VID 0 in netlink to set the
> >>> flag?
> >>>
> >>> Even in that case, I'm afraid that it might be confusing for developers
> >>> for the same reason. We are going to prohibit to specify VID with 0 (and
> >>> 4095) in adding/deleting a FDB entry or a vlan filtering entry, but it
> >>> would allow us to use VID 0 only when a vlan filtering entry is
> >>> configured.
> >>> I am thinking a new nlattr is a straightforward approach to configure
> >>> it.
> >>
> >> By making this an explicit attribute it makes vid 0 a special case for
> >> any automatic tool that would provision such filtering.  Seeing vid 0
> >> would mean that these tools would have to know that this would have to
> >> be translated to a different attribute instead of setting the policy
> >> values.
> >
> > Yes, I agree with you that we can do it by the way you explained.
> > What I don't understand is the advantage of using vid 0 over another way
> > such as adding a new nlattr.
> > I think we can indicate transmitting priority-tags explicitly by such a
> > nlattr. Using vid 0 seems to be easier to implement than a new nlattr,
> > but, for me, it looks less intuitive and more difficult to maintain
> > because we have to care about vid 0 instead of simply ignoring it.
> >
> 
> The point I am trying to make is that regardless of the approach someone
> has to know what to do when enabling priority tagged frames.  You 
> proposal would require the administrator or config tool to have that 
> knowledge.  Example is:
> 	Admin does: bridge vlan set priority on dev eth0
>          Automated app:
> 		if (vid == 0)
> 			/* Turn on priority tagged frame support */
> 
> My proposal would require the bridge filtering implementation to have it.
> 	user tool: bridge vlan add vid 0 tagged
> 	Automated app:  No special case.
> 
> IMO its better to have 1 piece code handling the special case then 
> putting it multiple places.

Thank you for the detailed explanation.
Now I understand your intention.

I have one question about your proposal.
I guess the way to enable priority-tagged is something like
	bridge vlan add vid 10 dev eth0
	bridge vlan add vid 10 dev vnet0 pvid untagged
	bridge vlan add vid 0 dev vnet0 tagged
where vnet0 has sub interface vnet0.0.

Here the admin have to know the egress policy is applied to a frame
twice in a certain order when it is transmitted from the port vnet0
attached, that is, first, a frame with vid 10 get untagged, and then, an
untagged frame get priority-tagged.

This behavior looks difficult to know without previous knowledge.
Any good idea to avoid such a need for the admin's additional knowledge?

> 
> Thanks
> -vlad
> 
> > Thanks,
> >
> > Toshiaki Makita
> >
> >>
> >> How it is implemented internally in the kernel isn't as big of an issue.
> >> We can do it as a separate flag or as part of existing policy.
> >>
> >> -vlad
> >>
> >>>
> >>> Thanks,
> >>>
> >>> Toshiaki Makita
> >>>
> >>>>
> >>>> -vlad
> >>>>
> >>>>>
> >>>>> Thanks,
> >>>>>
> >>>>> Toshiaki Makita
> >>>>>
> >>>>>>
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>>
> >>>>>>> Toshiaki Makita
> >>>>>>>
> >>>>>>>>
> >>>>>>>> --
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> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>
> >>>>>
> >>>>> --
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> >>>>> the body of a message to majordomo@...r.kernel.org
> >>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>>>
> >>>
> >>>
> >>
> >
> >


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