[DTrace-devel] [PATCH 15/19] Ignore clauses: some clauses are impossible regardless of uprp

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

In ignore_clauses, for an underlying probe uprp, we try to
decide if we can safely ignore clause n.

Meanwhile, for some clauses, the probe description tells us the
clause will not be called for any USDT probe, regardless of the
underlying probe.  For example, "syscall::write:" can safely be
ignored, for all uprp.

Add a dtsd_usdt variable to each statement to track status:

    USDT_FLAG_UNINITIALIZED  not yet initialized

    USDT_FLAG_POSSIBLE       clause could possibly be called
                             for some USDT probe

    USDT_FLAG_IGNORE         clause can safely be ignored for
                             all USDT probes

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_prov_uprobe.c | 56 ++++++++++++++++++++++++++++++++++++--
 libdtrace/dtrace.h         |  1 +
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/libdtrace/dt_prov_uprobe.c b/libdtrace/dt_prov_uprobe.c
index 883a3e9d..454c53dc 100644
--- a/libdtrace/dt_prov_uprobe.c
+++ b/libdtrace/dt_prov_uprobe.c
@@ -27,6 +27,7 @@
  */
 #include <sys/types.h>
 #include <assert.h>
+#include <ctype.h>
 #include <errno.h>
 #include <string.h>
 
@@ -232,6 +233,10 @@ grow_strtab(dtrace_hdl_t *dtp)
 	return 0;
 }
 
+#define USDT_FLAG_UNINITIALIZED	0
+#define USDT_FLAG_POSSIBLE	1
+#define USDT_FLAG_IGNORE	2
+
 /*
  * Judge whether clause "n" could ever be called as a USDT probe
  * for this underlying probe.
@@ -239,7 +244,53 @@ grow_strtab(dtrace_hdl_t *dtp)
 static int
 ignore_clause(dtrace_hdl_t *dtp, int n, const dt_probe_t *uprp)
 {
-	/* To be safe, ignore nothing. */
+	dtrace_probedesc_t	*pdp = &dtp->dt_stmts[n]->dtsd_ecbdesc->dted_probe;
+	int			*usdt_stat = &dtp->dt_stmts[n]->dtsd_usdt;
+
+	/*
+	 * Some clauses could never be called for a USDT probe,
+	 * regardless of the underlying probe uprp.  Cache this
+	 * status in dt_stmts[n]->dtsd_usdt (pointed to by usdt_stat).
+	 */
+	if (*usdt_stat == USDT_FLAG_UNINITIALIZED) {
+		char lastchar = pdp->prv[strlen(pdp->prv) - 1];
+
+		/*
+		 * If the last char in the provider description is
+		 * neither '*' nor a digit, it cannot be a USDT probe.
+		 */
+		if (lastchar != '*' && !isdigit(lastchar)) {
+			*usdt_stat = USDT_FLAG_IGNORE;
+			return 1;
+		}
+
+		/*
+		 * If the provider description is "pid[0-9]*", it
+		 * is a pid probe, not USDT.
+		 */
+		if (strncmp(pdp->prv, "pid", 3) == 0) {
+			int i, l = strlen(pdp->prv);
+
+			for (i = 3; i < l; i++)
+				if (!isdigit((pdp->prv[i])))
+					break;
+
+			if (i == l) {
+				*usdt_stat = USDT_FLAG_IGNORE;
+				return 1;
+			}
+		}
+
+		/* Otherwise, it is possibly a USDT probe. */
+		*usdt_stat = USDT_FLAG_POSSIBLE;
+	}
+	if (*usdt_stat == USDT_FLAG_IGNORE)
+		return 1;
+
+	/*
+	 * If USDT_FLAG_POSSIBLE, try to use uprp.
+	 */
+
 	return 0;
 }
 
@@ -267,7 +318,8 @@ static void update_uprobe(dtrace_hdl_t *dtp, void *datap)
 	 */
 	memset(&pcb, 0, sizeof(dt_pcb_t));
 	for (i = 0; i < dtp->dt_clause_nextid; i++)
-		dt_pid_create_probes(&dtp->dt_stmts[i]->dtsd_ecbdesc->dted_probe, dtp, &pcb, 1);
+		if (dtp->dt_stmts[i]->dtsd_usdt != USDT_FLAG_IGNORE)
+			dt_pid_create_probes(&dtp->dt_stmts[i]->dtsd_ecbdesc->dted_probe, dtp, &pcb, 1);
 
 	while (prid < dtp->dt_probe_id) {
 		dt_bpf_probe_t pinfo;
diff --git a/libdtrace/dtrace.h b/libdtrace/dtrace.h
index a23052e4..2de7067f 100644
--- a/libdtrace/dtrace.h
+++ b/libdtrace/dtrace.h
@@ -151,6 +151,7 @@ typedef struct dtrace_stmtdesc {
 	dtrace_attribute_t dtsd_stmtattr;	/* statement attributes */
 	int dtsd_clauseflags;			/* clause flags */
 	int dtsd_index;				/* index in dtp->dt_stmts */
+	int dtsd_usdt;				/* flags describing USDT use, see dt_prov_uprobe.c */
 } dtrace_stmtdesc_t;
 
 /* dtsd clause flags */
-- 
2.43.5