Re: [PATCH v2 3/4] public/io/netif: specify MTU override node

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Paul Durrant writes ("[PATCH v2 3/4] public/io/netif: specify MTU override 
node"):
> From: Paul Durrant <pdurrant@xxxxxxxxxx>
> 
> There is currently no documentation to state what MTU a frontend should
> adertise to its network stack. It has however long been assumed that the
> default value of 1500 is correct.
> 
> This patch specifies a mechanism to allow the tools to set the MTU via a
> xenstore node in the frontend area and states that the absence of that node
> means the frontend should assume an MTU of 1500 octets.
> 
> NOTE: The Windows PV frontend has used an MTU sampled from the xenstore
>       node specified in this patch.
> 
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

> +/*
> + * MTU
> + * ===
> + *
> + * The toolstack may set a value of MTU for the frontend by setting the
> + * /local/domain/<domid>/device/vif/<vif>/mtu node with the MTU value in
> + * octets. If this node is absent the frontend should assume an MTU value
> + * of 1500 octets. A frontend is also at liberty to ignore this value so
> + * it is only suitable for informing the frontend that a packet payload
> + * >1500 octets is permitted.
> + */

I find this wording a bit clumsy - a more formal treatment might be
better - but in my reading the overall semantics are correct.

Thanks,X
Ian.