[ofa-general] how to write a IB user level multicast application

[Dotan Barak]

Hi.

zhang Jackie wrote:
> hi,everyone!
>   I want to write a IB user level multicast application,but I find 
> only two functions related to multicast:*ibv_attach_mcast* and 
> *ibv_detach_mcast*, I  cant find any functions or any information in 
> work request for sending packets to a multicast group.for example,in 
> struct ibv_send_wr, struct ud must have a *remote_qpn *not a qp group.
>   Do anyone know how to write a user level multicast application? If 
> anyone knows ,please let me known, thanks.
In the following URL you can find a very simple example on how to use 
multicast:
https://svn.openfabrics.org/svn/openib/trunk/contrib/mellanox/ibtp/gen2/userspace/useraccess/multicast_test/multicast_test.c


If you want to use multicast in IB:
you need to do the following things:

receiver side:
--------------
create an UD QP
attach this QP to a multicast group
post RR to the RQ of this QP


sender side:
--------------
post the message to remote QP number of 0xffffff, dlid which is the 
multicast LID and GID of the multicast (in the GRH of the AH).


this test doesn't send an SA query (to get the multicast props) or an SA 
multicast join (to make the SM configure the subnet to make the port 
that this QP is attached to) to get the multicast messages.

This example will work on a back-to-back topology.

I hope this helped you
Dotan