Re: [PATCH] vxlan: Fix error that was resulting in VXLAN MTU size being 10 bytes too large

On 20 November 2012 03:03, Stephen Hemminger [off-list ref] wrote:

On Mon, 19 Nov 2012 22:33:50 +1100
Joseph Glanville [off-list ref] wrote:

quoted

On 14 November 2012 08:33, Stephen Hemminger [off-list ref] wrote:

quoted

On Tue, 13 Nov 2012 14:37:19 -0500 (EST)
David Miller [off-list ref] wrote:

quoted

From: Alexander Duyck <redacted>
Date: Fri, 09 Nov 2012 15:35:24 -0800

quoted

This change fixes an issue I found where VXLAN frames were fragmented when
they were up to the VXLAN MTU size.  I root caused the issue to the fact that
the headroom was 4 + 20 + 8 + 8.  This math doesn't appear to be correct
because we are not inserting a VLAN header, but instead a 2nd Ethernet header.
As such the math for the overhead should be 20 + 8 + 8 + 14 to account for the
extra headers that are inserted for VXLAN.

Signed-off-by: Alexander Duyck <redacted>

Applied, thanks for the detailed commit message.

Probably need smarter code there to look at header length requirement
of underlying device as well, maybe someone will be perverse and runn
vxlan over a tunnel or IPoIB.

Forgive my ignorance but why would running VXLAN on IPoIB require
special header handling? (and would it work or behave strangely?)

I was planning on giving this a go when 3.7 is released but I might do
that sooner if problems are anticipated.

quoted

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Joseph.

Some lower layers require bigger (or smaller headers). As it was, vxlan
was only allocating skb with a fixed amount of headroom. This would lead to
lower layers having to copy the skb.

My suggestion has already been addressed by a later patch.

Thankyou for the clarification, I found the patch about the lower_dev
hard_header_len!

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