[openib-general] Re: A Couple of User CM Questions

[Hal Rosenstock]

On Mon, 2005-05-09 at 15:32, Hal Rosenstock wrote:
> On Mon, 2005-05-09 at 14:39, Libor Michalek wrote: 
> > On Mon, May 09, 2005 at 01:22:17PM -0400, Hal Rosenstock wrote:
> > > Hi Libor,
> > > 
> > > I have a couple of questions pertaining to the user CM.
> > > 
> > > 1. It appears that device (and port) are not supported either incoming
> > > or outgoing. So if that is correct, I presume only the first device
> > > (first port) is the only one which can be expected to work. Correct ?
> > > If so, that should be added to README as a current limitation.
> 
> So I am presuming this is a current limitation.
> 
> > > 2. Any idea on how device would be supported ? Would this just be with
> > > an IB device number or a string like "mthca0" ?
> > 
> >   I was thinking that the destination GID in the req_event path record
> > would be sufficient to identify the local device/port, but I had not
> > taken a look at sidr_req_event. I think this is the correct GID to use
> > for creating the QP, but I have not taken a look at how easy it is to
> > turn a GID into a suitable device/portin user verbs. Thoughts?
> 
> and source GID (in the REQ primary path) on the active side ? 
> 
> That seems like it would work but wouldn't you need to walk the GID
> tables on each port on each IB device until you find the match ? Sounds
> a little expensive but would only be done once per connection.
> 
> The advantage of GID is this would be common across all IB devices. Not
> sure what else could be other than a deterministic numbering of IB
> devices locally which I believe does not currently exist.

ib_verbs does have a way to get_devices (ibv_get_devices) and specify
expose a pointer to a struct ibv_device. That would be another
alternative to using GIDs. That would make it similar to the kernel CM.

-- Hal