[openib-general] [PATCH] Allow setting of NodeDescription

[Jack Morgenstein]

Unless the Node Description is changed before QP0 on the HCA enters the RTS
state, there is no guarantee that the SM will receive the updated Node
Description string.

Note the following scenario (in which SM is already up-and-running on
another host in the network):
1. Local driver starts up
2. QP0 on local HCA enters RTS state
3. SM sweep occurs just after 2 above
4. Local SM agent provides SM with Node Description string as was specified
at HCA startup
5. SM provides SA with Node Description info, for the NodeRecord query for
each node in the net.
5. User now modifies Node Description to something else
6. NO guarantee that SM will pay attention to change of Node Description at
next sweep. (depends on SM implementation).
7. SA will then use the original Node Description string when responding to
a NodeRecord query.

The resulting set of NodeDescription strings present in the SM and SA could
then be a race-dependent salad (depending on the timing of QP0 entering RTS
state, SM subnet sweep, and resetting of the local NodeDescription string).

Jack

-----Original Message-----
From: Roland Dreier [mailto:rolandd at cisco.com]
Sent: Thursday, September 15, 2005 8:18 AM
To: Fab Tillier
Cc: openib-general at openib.org
Subject: Re: [openib-general] [PATCH] Allow setting of NodeDescription


    Fab> To me, non volatile in this context means something like
    Fab> using the system name.

Huh??  To me non-volatile means not changing.

    Fab> Would this be hard to do?  In fact, I would prefer to see the
    Fab> system name used instead of whatever is programmed in the HCA
    Fab> as the default.  Granted, this makes the node description
    Fab> burned in the firmware useless, but that doesn't seem like a
    Fab> big deal.

It's easy to do, but I don't want to put naming policy in the kernel.
I'll try to think of a clean way to give userspace a chance to set the
node description before the HCA ports are exposed to the SM.

However, there are various unsolvable cases like boot over IB, where
the HCA ports need to be active to mount the root filesystem, but the
system doesn't have its hostname set until after the root filesystem
is mounted.

 - R.
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