[openib-general] [RFC/PATCH] librdmacm: use the ipoib broadcast group qkey

[Michael S. Tsirkin]

> Quoting Sean Hefty <mshefty at ichips.intel.com>:
> Subject: Re: [RFC/PATCH] librdmacm: use the ipoib broadcast group qkey
> 
> Or Gerlitz wrote:
> > Modify librdmacm use a qkey for its UD IDs/QPs delivered to it by the
> > rdma cm kernel code instead the a hard coded RDMA_UD_QKEY. For RDMA_PS_UDP
> > ID, the qkey is provided by the kernel in ADDR_RESOLVED and CONNECT_REQUEST
> > events and is stored by the library in struct cma_id_private. Later
> > the library use the qkey when it is called to create a UD QP.
> 
> Reading the code, the following sequence does not work: rdma_join_multicast then 
> rdma_create_qp.  The QP does not automatically attach to previously joined 
> multicast groups on creation.  (This is a problem with the existing code.)  The 
> reverse sequence (create then join) does work.  I'm adding the ipoib support to 
> the librdmacm now, but we will still need a separate patch to fix attaching to 
> joined multicast groups when the QP is created.

Maybe just ask user to always call rdma_join_multicast after rdma_create_qp?
Joins are now properly reference counted, so it shouldn't be a problem
to repeat this any number of times. Right?

-- 
MST