[PATCH v2 lttng-ust] Introduce vtracef

* [PATCH v2 lttng-ust] Introduce vtracef
@ 2020-02-05 23:36 Maxime Roussin-Belanger
  2020-02-06  1:17 ` Simon Marchi
  2020-02-06 15:06 ` Mathieu Desnoyers
  0 siblings, 2 replies; 5+ messages in thread
From: Maxime Roussin-Belanger @ 2020-02-05 23:36 UTC (permalink / raw)
  To: lttng-dev, champagne.guillaume.c

vtracef accepts a va_list argument to simplify tracing
functions which use a va_list

Here's an example from wpa_supplicant that I wanted to
trace:

void wpa_debug(int level, const char* fmt, ...) {

    va_list ap;
    va_start(ap, fmt);

    ...
    // The call I want to easily trace with vtracef
    vprintf(fmt, ap);

    ...
    va_end(ap);
}

wpa_debug is used a fair amount and it would be annoying to
replace all the wpa_debug calls with tracef.

With vtracef, it simplifies the find and replace effort by
only changing it at one place.

Signed-off-by: Maxime Roussin-Belanger <maxime.roussinbelanger@gmail.com>
---
Changes in v2:
	- Add man page
	- Add an example
	- Remove ifdef to guard against systemtap not having va_list

doc/examples/demo-tracef/Makefile       | 14 +++++-
 doc/examples/demo-tracef/demo-vtracef.c | 58 +++++++++++++++++++++++++
 doc/man/tracef-tracelog-limitations.txt |  3 ++
 doc/man/tracef.3.txt                    | 15 ++++---
 include/lttng/tracef.h                  |  8 ++++
 liblttng-ust/tracef.c                   | 18 +++++---
 6 files changed, 101 insertions(+), 15 deletions(-)
 create mode 100644 doc/examples/demo-tracef/demo-vtracef.c

diff --git a/doc/examples/demo-tracef/Makefile b/doc/examples/demo-tracef/Makefile
index ee207843..809aac19 100644
--- a/doc/examples/demo-tracef/Makefile
+++ b/doc/examples/demo-tracef/Makefile
@@ -20,18 +20,28 @@ LIBS = -ldl -llttng-ust	# On Linux
 LOCAL_CPPFLAGS += -I.
 AM_V_P := :
 
-all: demo-tracef
+all: demo-tracef demo-vtracef
 
 demo-tracef.o: demo-tracef.c
 	@if $(AM_V_P); then set -x; else echo "  CC       $@"; fi; \
 		$(CC) $(CPPFLAGS) $(LOCAL_CPPFLAGS) $(AM_CFLAGS) $(AM_CPPFLAGS) \
 		$(CFLAGS) -c -o $@ $<
 
 demo-tracef: demo-tracef.o
 	@if $(AM_V_P); then set -x; else echo "  CCLD     $@"; fi; \
 		$(CC) $(LDFLAGS) $(AM_CFLAGS) $(AM_LDFLAGS) $(CFLAGS) \
 		-o $@ $< $(LIBS)
 
+demo-vtracef.o: demo-vtracef.c
+	@if $(AM_V_P); then set -x; else echo "  CC       $@"; fi; \
+		$(CC) $(CPPFLAGS) $(LOCAL_CPPFLAGS) $(AM_CFLAGS) $(AM_CPPFLAGS) \
+		$(CFLAGS) -c -o $@ $<
+
+demo-vtracef: demo-vtracef.o
+	@if $(AM_V_P); then set -x; else echo "  CCLD     $@"; fi; \
+		$(CC) $(LDFLAGS) $(AM_CFLAGS) $(AM_LDFLAGS) $(CFLAGS) \
+		-o $@ $< $(LIBS)
+
 .PHONY: clean
 clean:
-	rm -f *.o *.a demo-tracef
+	rm -f *.o *.a demo-tracef demo-vtracef
diff --git a/doc/examples/demo-tracef/demo-vtracef.c b/doc/examples/demo-tracef/demo-vtracef.c
new file mode 100644
index 00000000..8eaccf61
--- /dev/null
+++ b/doc/examples/demo-tracef/demo-vtracef.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2020  Maxime Roussin-Belanger
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; version 2.1 of
+ * the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include <lttng/tracef.h>
+
+
+void print_debug(const char* msg, ...) {
+	va_list ap;
+	va_start(ap, msg);
+
+	vtracef(msg, ap);
+
+	va_end(ap);
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+	int delay = 0;
+	const char *str = "mystring test";
+	long l = 0x42;
+
+	if (argc == 2)
+		delay = atoi(argv[1]);
+
+	fprintf(stderr, "Demo program starting.\n");
+
+	sleep(delay);
+
+	fprintf(stderr, "Tracing... ");
+
+	for (i = 0; i < 5; i++)
+	{
+		print_debug("This is a \"%s\" formatted %d event %lx", str, i, l);
+	}
+	fprintf(stderr, " done.\n");
+	return 0;
+}
diff --git a/doc/man/tracef-tracelog-limitations.txt b/doc/man/tracef-tracelog-limitations.txt
index a9491903..ad4130dd 100644
--- a/doc/man/tracef-tracelog-limitations.txt
+++ b/doc/man/tracef-tracelog-limitations.txt
@@ -21,4 +21,7 @@ Thus, +{macro-name}()+ is useful for quick prototyping and debugging, but
 should not be considered for any permanent/serious application
 instrumentation.
 
++v{macro-name}()+ does not have a `STAP_PROBEV()` call, because `STAP_PROBEV()`
+does not support `va_list`. If you need it, you should emit this call yourself.
+
 See man:lttng-ust(3) to learn more about custom tracepoint providers.
diff --git a/doc/man/tracef.3.txt b/doc/man/tracef.3.txt
index 1068afad..b54a1623 100644
--- a/doc/man/tracef.3.txt
+++ b/doc/man/tracef.3.txt
@@ -5,43 +5,44 @@ tracef(3)
 
 NAME
 ----
-tracef - LTTng-UST printf(3)-like interface
+tracef, vtracef - LTTng-UST printf(3)-like interface
 
 
 SYNOPSIS
 --------
 [verse]
 *#include <lttng/tracef.h>*
 
 [verse]
 #define *tracef*('fmt', ...)
+#define *vtracef*('fmt', va_list ap)
 
 Link with `-llttng-ust`.
 
 
 DESCRIPTION
 -----------
 The LTTng-UST `tracef()` API allows you to trace your application with
 the help of a simple man:printf(3)-like macro. The 'fmt' argument is
 passed directly to the 'fmt' parameter of man:vasprintf(3), as well as
 the optional parameters following 'fmt'.
 
-To use `tracef()`, include `<lttng/tracef.h>` where you need it, and
-link your application with `liblttng-ust`. See the <<example,EXAMPLE>>
+To use `tracef()` or `vtracef()`, include `<lttng/tracef.h>` where you need it,
+and link your application with `liblttng-ust`. See the <<example,EXAMPLE>>
 section below for a complete usage example.
 
-Once your application is instrumented with `tracef()` calls and
+Once your application is instrumented with `tracef()` or `vtracef()` calls and
 ready to run, use man:lttng-enable-event(1) to enable the
 `lttng_ust_tracef:*` event.
 
-The `tracef()` events contain a single field, named `msg`, which is the
-formatted string output.
+The `tracef()` events contain a single field, named `msg`,
+which is the formatted string output.
 
 If you need to attach a specific log level to a `tracef()` call, use
 man:tracelog(3) instead.
 
 See also the <<limitations,LIMITATIONS>> section below for important
-limitations to consider when using `tracef()`.
+limitations to consider when using `tracef()` or `vtracef()`.
 
 
 [[example]]
diff --git a/include/lttng/tracef.h b/include/lttng/tracef.h
index 0c59c9ae..854ccdce 100644
--- a/include/lttng/tracef.h
+++ b/include/lttng/tracef.h
@@ -32,13 +32,21 @@ extern "C" {
 extern
 void _lttng_ust_tracef(const char *fmt, ...);
 
+extern
+void _lttng_ust_vtracef(const char *fmt, va_list ap);
+
 #define tracef(fmt, ...)						\
 	do {								\
 		LTTNG_STAP_PROBEV(tracepoint_lttng_ust_tracef, event, ## __VA_ARGS__); \
 		if (caa_unlikely(__tracepoint_lttng_ust_tracef___event.state)) \
 			_lttng_ust_tracef(fmt, ## __VA_ARGS__);		\
 	} while (0)
 
+#define vtracef(fmt, ap)						\
+	do {								\
+		if (caa_unlikely(__tracepoint_lttng_ust_tracef___event.state)) \
+			_lttng_ust_vtracef(fmt, ap);		\
+	} while (0)
 #ifdef __cplusplus
 }
 #endif
diff --git a/liblttng-ust/tracef.c b/liblttng-ust/tracef.c
index ea98e43e..1311f0d5 100644
--- a/liblttng-ust/tracef.c
+++ b/liblttng-ust/tracef.c
@@ -29,20 +29,26 @@
 #define TRACEPOINT_DEFINE
 #include "lttng-ust-tracef-provider.h"
 
-void _lttng_ust_tracef(const char *fmt, ...)
+void _lttng_ust_vtracef(const char *fmt, va_list ap)
 {
-	va_list ap;
 	char *msg;
-	int len;
-
-	va_start(ap, fmt);
-	len = vasprintf(&msg, fmt, ap);
+	const int len = vasprintf(&msg, fmt, ap);
 	/* len does not include the final \0 */
 	if (len < 0)
 		goto end;
 	__tracepoint_cb_lttng_ust_tracef___event(msg, len,
 		LTTNG_UST_CALLER_IP());
 	free(msg);
 end:
+	return;
+}
+
+void _lttng_ust_tracef(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	_lttng_ust_vtracef(fmt, ap);
+
 	va_end(ap);
 }
-- 
2.20.1

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