Fwd: Re: [openib-general] static LID computationwithTS_HOST_DRIVER

[Tillier, Fabian]

> From: Roland Dreier [mailto:roland at topspin.com]
> Sent: Wednesday, September 29, 2004 5:09 PM
> 
>     Yaron> A better solution that IBTA needs to look at is creating a
>     Yaron> well known Loopback LID value that apps use when they want
>     Yaron> to talk locally (like IP 127...)
> 
> If/when IBTA specifies this and available hardware implements this,
> then this will be a great solution.
> 
> In the meantime, I don't see a problem with having a mechanism to
> provide an initial value for PortInfo:LID _before_ the SM discovers
> the node.  The SM must be able to deal with arbitrary values of this
> field, since it can't make any assumptions about the state of the
> subnet.  I don't think the spec forbids having a mechanism to specify
> the initial value of PortInfo:LID.
> 
> I agree that the spec places the SM under no obligation to preserve
> the LIDs it finds.  However, if someone wants to run an application
> that requires loopback connections to be preserve, I see no problem
> with requiring an SM that provides an administrative mechanism for
> static LID assignment.
> 
> The advantage of this scheme is that it requires no modifications to
> either the IB spec or existing IB hardware.
> 

To add to this, I think it is quite likely that an administrator would
be setting such static LIDs - the IPoIB code won't just pick a LID out
of the blue.  This administrator is likely going to be the same
administrator that configures the SM to use LMC > 1.  I think we can
trust that such an administrator will do what they can such that any
statically assigned LIDs can be preserved with whatever SM settings they
use.  If they don't then they're a lousy administrator, and deserve to
have their LIDs reassigned.

- Fab