[lttng-dev] [PATCH v2 lttng-ust] Introduce vtracef
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Thu Feb 6 10:06:44 EST 2020
----- On Feb 5, 2020, at 6:36 PM, Maxime Roussin-Belanger maxime.roussinbelanger at gmail.com wrote:
> 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, ...) {
Please follow the coding style of lttng-ust for this changelog
and within the entire patch:
functions:
void myfunc(void)
{
}
for loop:
for (expression) {
}
Thanks,
Mathieu
>
> 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 at 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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--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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