[openib-general] modifying queue pair attributes - librdmacm

[Sean Hefty]

> struct ibv_qp_attr attr = {
>                .path_mtu               = IBV_MTU_2048
>        };
>        if (ibv_modify_qp(cb->qp, &attr, IBV_QP_PATH_MTU) ){
>                fprintf(stderr, "Failed to modify QP\n");
>                fprintf(stderr, "%s \n\n", strerror(errno) );
>                return 1;
>        }
>
>
>And, it fails to do the job (The error string comes up with "Invalid
>argument".)! I can't find any function in librdmacm which allows us to
>modify the queue pair attributes. What am I doing wrong ?

The path MTU should be set when transitioning the QP from INIT to RTR as part of
the remote node address vector.  The rdmacm sets this based on the path record
that it obtains from route resolution.  Although the kernel allows users to
modify the QP, this functionality has not been exposed through the userspace
APIs.

- Sean