[ovs-dev] [PATCH] datapath: Fix VLAN insertion behavior on Linux 2.6.27 and 2.6.28.

[Jesse Gross]

On Thu, May 27, 2010 at 1:03 PM, Ben Pfaff <blp at nicira.com> wrote:

> The behavior of __vlan_put_tag() has changed over time:
>
>     - In 2.6.26 and earlier, it adjusted both MAC and network header
>       pointers.  (The latter didn't make any sense.)
>
>     - In 2.6.27 and 2.6.28, it did not adjust any header pointers at all.
>
>     - In 2.6.29 and later, it adjusts the MAC header pointer only.
>
> The behavior in 2.6.26 and earlier, and in 2.2.29 and later, works OK for
> Open vSwitch.  The 2.6.27 and 2.6.28 behavior *almost* works OK, with a few
> subtle problems.  If an action that sets a VLAN tag is followed by an
> action that strips a VLAN tag, the "strip" action silently fails.  This is
> because vlan_pull_tag() in datapath/actions.c sees the encapsulated
> protocol, not the 802.1Q protocol, because the MAC header was not adjusted
> and does not point to the 802.1Q header.  If multiple set-VLAN actions
> occur in a single flow, the second and later actions will fail for the same
> reason.
>
> This commit fixes the problem by ensuring that __vlan_put_tag() always
> behaves as in 2.6.29 and later.
>
> Reported-by: Reid Price <reid at nicira.com>
> Bug #2867.
>

Looks good.

Justin actually posted about part of this issue several years ago:
http://www.mail-archive.com/netdev@vger.kernel.org/msg50550.html

Obviously it took a little while before it got straightened out...
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