Re: [Xen-devel] [PATCH v3 4/4] docs: Document xenstore paths for domain network address information

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
> Sent: 13 November 2015 16:18
> To: Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Ian Campbell; Jan Beulich; Keir (Xen.org);
> Tim (Xen.org)
> Subject: Re: [PATCH v3 4/4] docs: Document xenstore paths for domain
> network address information
> 
> Paul Durrant writes ("[PATCH v3 4/4] docs: Document xenstore paths for
> domain network address information"):
> > +#### ~/attr/vif/$DEVID/name = STRING [w]
> 
> You need to explicitly state what this information is to be used for.
> 
> This "name" is presumably useful for humans in the management UI ?
> You need to say something about the toolstack not trusting it too
> much.
> 
> > +A domain may write its internal 'friendly' name for a network device
> > +using this path.
> > +
> > +#### ~/attr/vif/$DEVID/mac/$INDEX = MAC_ADDRESS [w]
> > +
> > +A domain may write the set of MAC addresses (unicast and multicast)
> > +in use by the network frontend using paths of this form.
> 
> The primary (virtual hardware) VIF MAC address is already recorded by
> the toolstack in the PV protocol backend directory.
> 
> What is this for ?
> 

The frontend is free to ignore it and Windows has such override mechanisms. I 
view the address in the backend area as the virtual NIC's burnt-in address. 
This area is for the displaying all MAC addresses for which the frontend is 
processing traffic i.e. current unicast and all multicast addresses in 
operation. (No point in making broadcast address explicit).

> At the very least you need to state that this information MUST NOT be
> used for packet routing, packet filtering, or for security purposes.
> 

It is for information only. I'll call that out.

> > +#### ~/attr/vif/$DEVID/ipv4/$INDEX = IPV4_ADDRESS [w]
> > +#### ~/attr/vif/$DEVID/ipv6/$INDEX = IPV6_ADDRESS [w]
> 
> I can see that this would be easier to use than messing with querying
> the DHCP server or whatever.
> 
> But you absolutely must state that this information MUST NOT be used
> for packet routing etc.  Examples of what it _is_ good for would be
> good.
> 

Mostly for display purposes, but a UI could use it for kicking off a VNC or SSH 
session... I'll add that to the doc.

  Paul

> Thanks,
> Ian.

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