[DTrace-devel] [PATCH] probe: ensure probe argument info is retrieved only once per probe

[Kris Van Hees]

Throughout the compilation process there are multiple points where
probe argument information is requested from the providers.  This
data cannot change during a runtime of DTrace and there is therefore
no reason to go through the process of retrieving it more than once.

The prp->argc (probe argument count) is used to determine if argument
data has been obtained.  It is initially -1, and will be 0 or greater
once argument data has been requested.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_probe.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libdtrace/dt_probe.c b/libdtrace/dt_probe.c
index 3594097e..58b26836 100644
--- a/libdtrace/dt_probe.c
+++ b/libdtrace/dt_probe.c
@@ -695,6 +695,7 @@ dt_probe_insert(dtrace_hdl_t *dtp, dt_provider_t *prov, const char *prv,
 	prp->desc = desc;
 	prp->prov = prov;
 	prp->prv_data = datap;
+	prp->argc = -1;
 
 	dt_htab_insert(dtp->dt_byprv, prp);
 	dt_htab_insert(dtp->dt_bymod, prp);
@@ -865,13 +866,18 @@ dt_probe_args_info(dtrace_hdl_t *dtp, dt_probe_t *prp)
 	int			i, nc, xc;
 	dtrace_typeinfo_t	dtt;
 
+	/* Only retrieve probe argument information once per probe. */
+	if (prp->argc != -1)
+		return;
 	if (!prp->prov->impl->probe_info)
 		return;
 	if (prp->prov->impl->probe_info(dtp, prp, &argc, &argv) < 0)
 		return;
 
-	if (!argc || !argv)
+	if (!argc || !argv) {
+		prp->argc = 0;
 		return;
+	}
 
 	nc = 0;
 	for (xc = 0; xc < argc; xc++)
-- 
2.39.1