Re: [Xen-devel] [PATCH 5/7] xen-netfront: reduce gso_max_size to account for ethernet header

[Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>]

On Fri, 2013-04-12 at 09:18 +0100, Ian Campbell wrote:
> On Thu, 2013-04-11 at 21:04 +0100, Wei Liu wrote:
> > On Tue, Apr 09, 2013 at 12:07:33PM +0100, Wei Liu wrote:
> > > The maximum packet including ethernet header that can be handled by 
> > > netfront /
> > > netback wire format is 65535. Reduce gso_max_size accordingly.
> > > 
> > > Drop skb and print warning when skb->len > 65535. This can 1) save the 
> > > effort
> > > to send malformed packet to netback, 2) help spotting misconfiguration of
> > > netfront in the future.
> > > 
> > 
> > Any opinion on how much space should be reserved? From a previous thread
> > Ben seemed to suggest 90 (Ethernet + VLAN tag + IPv6 + TCP + timestamp
> > option = 90 bytes).
> 
> I trust Ben and that seems as good as anything to me.

I don't know the TCP or the GSO forwarding code well enough to be
certain.  So don't simply trust me on this.

Ben.

> Is this the sort of limit others might be interested in, should we have
> a global #define?

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.


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