netdev - Re: [PATCH v2.44 1/5] odp: Allow VLAN actions after MPLS actions

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Date:	Tue, 22 Oct 2013 13:55:41 -0700
From:	Ben Pfaff <blp@...ira.com>
To:	Joe Stringer <joestringernz@...il.com>
Cc:	Simon Horman <horms@...ge.net.au>, dev@...nvswitch.org,
	netdev@...r.kernel.org, Jesse Gross <jesse@...ira.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	Ravi K <rkerur@...il.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH v2.44 1/5] odp: Allow VLAN actions after MPLS actions

On Tue, Oct 22, 2013 at 11:30:26AM -0700, Joe Stringer wrote:
> You're quite right. I think for OF1.2, this is similar to existing
> behaviour, but for OF1.3 it's just incorrect. There is an additional issue
> with the LOAD action.
> 
> OF1.2:
> "push_vlan(A),push_mpls,push_vlan(B)"
> In OF1.2, this has the same result as:-
> "push_mpls,push_vlan(A),push_vlan(B)"
> 
> When translated, this boils down to "(pop_vlan,)push_mpls,push_vlan(B)".
> Correct me if I am wrong, but I think this is similar to the existing
> behaviour, as we currently only support one layer of VLAN. It doesn't
> matter if A == B.
> 
> OF1.3:
> "mod_vlan_vid:A,push_mpls:0x8847,mod_vlan_vid:A" should work, but the
> second mod_vlan is being dropped as it has the same VID as the first. This
> is incorrect, as you point out.
> 
> LOAD:
> "load:A->OXM_OF_VLAN_VID,push_mpls:0x8847,load:A->OXM_OF_VLAN_VID" doesn't
> result in the correct vlan_vid from the first load action. I'm not sure
> that vlan_tci_restore() is clear or correct---I believe its original
> purpose was to properly handle the case where MPLS changes are made from
> REG_LOAD and friends, in the way that the PUSH_MPLS case works. Instead, it
> is handling all cases where MPLS actions have been applied in the past,
> whether the current action modifies MPLS or not.
> 
> It's probably also worthwhile to make use of the ovs-ofctl monitor "-m"
> option in the tests to actually verify these, rather than the current tests
> where we just check the size of the resulting packet.

Thanks for the careful analysis.
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