Re: Fwd: Re: [openib-general] static LID computation with TS_HOST_DRIVER

[David M. Brean]

The subnet management state is protected by an M_Key (see section 
14.2.4).  The M_Key is managed by the SM.  The M_Key is not exposed via 
the Verbs or through SA queries [the exception being the trusted entity, 
but that entity is another SA or higher layer management application - 
so let's ignore for this situation.]   An endnode implementation should 
not allow any back-door mechanism that enables changing the subnet 
management state without the M_Key if the port is protected.  Note, the 
M_Key and protection bits can be in persistent storage and preserved 
across port power cycles to eliminate the power-up exposure.  So, 
without making subnet assumptions/restrictions, there is no reliable way 
for an IB client, like the local MAD layer, to specify the LID.

LID assignment is SM policy and the SM may choose to preserve a port's 
LID, however, I don't think IB clients should depend on this behavior.

-David
Roland Dreier wrote:
   David> Ok.  How does the port inform the SM that it has a
   David> "preferred" LID?
The port will already have a LID assigned when the SM discovers it.
My understanding is that the SM is "encouraged" to preserve a port's
LID if it doesn't conflict with any other LIDs, and this is what we're
relying on.
- Roland
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