Re: rdma_get_cm_event error behaviour defined?

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Leon Romanovsky (leon@kernel.org) wrote:
> On Mon, May 17, 2021 at 11:06:35AM +0100, Dr. David Alan Gilbert wrote:
> > Hi,
> >   Is 'rdma_get_cm_event's behaviour in initialising **event
> > defined in the error case?
> >   We don't see anything in the manual page, my reading of the
> > code is it's not set/changed in the case of failure - but is
> > that defined?
> >   It would be good if the manpage could explicitly state it.
> 
> AFAIK, the general practice do not rely on any output argument if
> function returns an error and I'm not sure that the man update is
> needed.

The case we had was whether we needed to clean up or not in the error
case; the original code in qemu was:

    2496     ret = rdma_get_cm_event(rdma->channel, &cm_event);
    2497     if (ret) {
    2498         perror("rdma_get_cm_event after rdma_connect");
    2499         ERROR(errp, "connecting to destination!");
    2500         rdma_ack_cm_event(cm_event);
    2501         goto err_rdma_source_connect;
    2502     }

and Li spotted that rdma_ack_cm_event  would seg in the case
rdma_get_cm_event failed.

While I agree on not relying on an output; without a definition you're
stuck between not knowing if you're leaking an event that should
have been cleaned up.

Dave

> Thanks
> 
> > 
> > Dave
> > -- 
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> > 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK