We decided to skip branch merges to Nevada builds 113-116. We had issues with the hardware in the lab and vboxes. Plus we wanted a stable environment for the BakeAThon. I'm having a hard time merging with build 117. One of the issues was a panic on the client (which I could patch) due to getting NFS4ERR_BADSESSION from a DS. I was able to see the DS replying on the exchange_id request in a packet trace. There are only a handful of places where the server returns this error code, so I was pretty sure I could reuse a Dtrace script I had laying around:

:nfssrv:mds_lease_chk:return
/args[1] != 0/
{
        printf("rc1 = %d", args[1]);
}

Until I came along this code snippet:

                                *cs->statusp = resp->dsr_status =
                                    NFS4ERR_UNSAFE_COMPOUND;
                                goto final;
...
final:
        DTRACE_NFSV4_2(op__destroy__session__done,
            struct compound_state *, cs,
            DESTROY_SESSION4res *, resp);
}

Just great, no return value. How could I catch it?

Well, the answer is staring us right in the face, we can use op__destroy__session__done. I had to snoop around for examples in a colleague's home directory (which is kinda why I blog about this stuff, it is easier to find), but ended up with this:

:::op-bind-conn-to-session-done
{
        bresp = (BIND_CONN_TO_SESSION4res *)arg1;

        printf("rc1 = %d", bresp->bctsr_status);
}

:::op-destroy-session-done
{
        dresp = (DESTROY_SESSION4res *)arg1;

        printf("rc1 = %d", dresp->dsr_status);
}

Note that I wasn't too worried about being specific as to which module you found these calls in, I was betting on them being very unique.

Oh, and I was able to narrow down where the NFS4ERR_BADSESSION was coming from. And then I had to add debug statements to find out why. :-< I bet I might have been able to do it still with Dtrace. :->