[DTrace-devel] [PATCH v2-alternative] Implement the io provider

[Eugene Loh]

I cannot vouch for the details of how the io stack works, but the use of 
tracepoints instead of fbt sure makes this stuff look nicer!  So,
     Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
though I'm not sure if I'm an eligible reviewer.

There continue to be some intermittent test failures.

Also (haven't thought about this yet), I see XFAIL "io:::start not fully 
supported before 5.15" for
     tst.fbt_probes.sh
     tst.nfs2.sh
     tst.wait.sh
Should there also be such a .x for
     tst.nfs.sh
???

Also, with UEK6 (also need to think about this more), I get problems 
with wait-* probes:
         # dtrace -n 'io:::start { exit(0) }'
         dtrace: description 'io:::start ' matched 1 probe
         CPU     ID                    FUNCTION:NAME
           7  98772                           :start

         # dtrace -n 'io:::done { exit(0) }'
         dtrace: description 'io:::done ' matched 1 probe
         CPU     ID                    FUNCTION:NAME
           7  98773                            :done

         # dtrace -n 'io:::wait-start { exit(0) }'
         dtrace: description 'io:::wait-start ' matched 1 probe
         dtrace: could not enable tracing: Module does not contain any 
CTF data
         # dtrace -n 'io:::wait-done { exit(0) }'
         dtrace: description 'io:::wait-done ' matched 1 probe
         dtrace: could not enable tracing: Module does not contain any 
CTF data

Also, the last arg to io_xfs_args() seems not to be used and therefore 
could be dropped.

And...

On 11/16/23 11:28, Eugene Loh via DTrace-devel wrote:
> diff --git a/libdtrace/dt_prov_io.c b/libdtrace/dt_prov_io.c
> +
> +	/* Handle the non-XFS wait-done flavor. */
> +	if (strcmp(prp->desc->prb, "wait-done") == 0) {
> +		/*
> +		 * We need instrument submit_bio_wait(struct bio *):
> +		 *   - on entry, store the bio pointer into a TLS var
> +		 *   - on return, retrieve the pointer (and clear the TLS var)
> +		 * We use a TLS var to distinguish among possible concurrent
> +		 * submit_bio_wait() on the CPU.
> +		 */

We need instrument...
->
We need to instrument...

> diff --git a/test/unittest/io/dump_io_probe_args.d b/test/unittest/io/dump_io_probe_args.d
> +io:::wait-start,
> +io:::wait-done,
> +io:::start,
> +io:::done
> +{
> +	printf("%s: %s: %s: %11s %d %3x  %9d %9d   %p %d %d  %5d %5d    %p   %d %d %d   %d %d %d %s %s %s\n",
> +	    probeprov, probemod, probefunc, probename,
> +	    arg1,

I think that should be arg2.  args[1] is also being dumped.  Here, we're 
trying to check that arg2==0.

Also, I think you changed some wording in check_io_probe_args.sh.  I 
guess that's okay, but in light of the fact that we're checking arg2 
here rather than args[2], the original wording might be better.

> +
> +	    args[0]->b_flags,
> +
> +	    args[0]->b_bcount,
> +	    args[0]->b_bufsize,