Fwd: Re: [openib-general] static LID computation withTS_HOST_DRIVER

[David M. Brean]

David M. Brean wrote:

> The IBA provides two mechanisms for updating subnet management data:
>
> 1) through the verbs - see Modify HCA (section 11.2.1.3)
> 2) through Subnet management packets (SMPs) - see Subnet Management
> Class (section 14.2)
>
> The IBA only supports updating the LID via SMPs (#2 above) and an entity
> using SMPs must have the M_Key.  If that entity doesn't have the M_Key,
> then it can't reliably change the LID.
>
> In addition, the IBA allows an endnode to request, through the verbs
> interface provided for the "node reinitialization" (see 14.4.4)
> mechanism, that subnet management state, such as the LID, be 
> preserved, when a port transitions through the DOWN state.  However, 
> the SM may not honor that request so the endnode must handle that 
> possibility because LID assignment policy is owned by the SM.  
> Furthermore, this mechanism is used on ports that have previously been 
> initialized by the SM (maybe that's why it's called the 
> reinitialization function :)).
>
> Given the mechanisms in the specification, I think that its possible 
> to have IB clients use loopback, even under the endnode power-up 
> scenario, while the port is not in the ACTIVE state and have them 
> continue without disruption when the port is made ACTIVE on the subnet 
> by the SM with use of the reinitialization mechanism.  This is a very 
> useful mechanism for various failover situations.
>
Loopback with reinitialization properly applied....

-David

> There is no current IBA mechanism or protocol for an endnode to set 
> just the LID, even if it had the M_Key, and have the SM preserve that 
> value.
>
> -David
>
> Roland Dreier wrote:
>
>> I don't see anything in the spec that forbids a CA from having an
>> arbitrary value in PortInfo:LID after initialization but before the SM
>> discovery (please correct me if I missed something).  I also don't see
>> anything that forbids an SM implementation from providing a mechanism
>> for preserving the LIDs it finds or administratively assigning LIDs.
>>
>> Of course none of this is required but I don't see a problem with
>> allowing it.
>>
>
>
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