[DTrace-devel] [PATCH 7/7] Report an error to the consumer if a probe cannot be enabled

[Kris Van Hees]

On Tue, Dec 06, 2022 at 06:00:11PM -0500, Eugene Loh via DTrace-devel wrote:
> Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
> One question below:
> 
> On 12/6/22 16:50, Kris Van Hees via DTrace-devel wrote:
> > Some probes (esp. uprobes) appear to be useable, but yet the kernel
> > tracing subsystem reports a failure when trying to enable the probe.
> > It need not be a fatal error (esp. when probing a set of probes based
> > on a wildcard specification), but it should get reported.
> > 
> > Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> > ---
> >   libdtrace/dt_bpf.c         | 20 +++++++++++++++++---
> >   libdtrace/dt_provider_tp.c |  4 ++--
> >   2 files changed, 19 insertions(+), 5 deletions(-)
> > 
> > diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> > index 92cbc4ed..a9536511 100644
> > --- a/libdtrace/dt_bpf.c
> > +++ b/libdtrace/dt_bpf.c
> > @@ -1044,7 +1044,8 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
> >   	 */
> >   	for (prp = dt_list_next(&dtp->dt_enablings); prp != NULL;
> >   	     prp = dt_list_next(prp)) {
> > -		int		fd;
> > +		int	fd;
> > +		int	rc = -1;
> >   		/* Already done. */
> >   		if (prp == dtp->dt_error)
> > @@ -1070,9 +1071,22 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
> >   		dt_difo_free(dtp, dp);
> > -		if (!prp->prov->impl->attach ||
> > -		    prp->prov->impl->attach(dtp, prp, fd) < 0)
> > +		if (prp->prov->impl->attach)
> > +		    rc = prp->prov->impl->attach(dtp, prp, fd);
> > +
> > +		if (rc == -ENOTSUPP) {
> > +			char	*s;
> > +
> > +			if (asprintf(&s, "Failed to enable %s:%s:%s:%s",
> > +				     prp->desc->prv, prp->desc->mod,
> > +				     prp->desc->fun, prp->desc->prb) == -1)
> > +				return dt_set_errno(dtp, EDT_ENABLING_ERR);
> > +			dt_handle_rawerr(dtp, s);
> > +			free(s);
> 
> Should there also be a close(fd) here?

Oops, yes.

> > +		} else if (rc < 0) {
> > +			close(fd);
> >   			return dt_set_errno(dtp, EDT_ENABLING_ERR);
> > +		}
> >   	}
> >   	return 0;
> > diff --git a/libdtrace/dt_provider_tp.c b/libdtrace/dt_provider_tp.c
> > index fdd7f9c5..7388bb94 100644
> > --- a/libdtrace/dt_provider_tp.c
> > +++ b/libdtrace/dt_provider_tp.c
> > @@ -74,13 +74,13 @@ dt_tp_attach(dtrace_hdl_t *dtp, tp_probe_t *tpp, int bpf_fd)
> >   		fd = perf_event_open(&attr, -1, 0, -1, 0);
> >   		if (fd < 0)
> > -			return dt_set_errno(dtp, errno);
> > +			return -errno;
> >   		tpp->event_fd = fd;
> >   	}
> >   	if (ioctl(tpp->event_fd, PERF_EVENT_IOC_SET_BPF, bpf_fd) < 0)
> > -		return dt_set_errno(dtp, errno);
> > +		return -errno;
> >   	return 0;
> >   }
> 
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